import AppKit
import SwiftUI
import Foundation
import Bonsplit
import CoreVideo
import Combine

// MARK: - Tab Type Alias for Backwards Compatibility
// The old Tab class is replaced by Workspace
typealias Tab = Workspace

enum NewWorkspacePlacement: String, CaseIterable, Identifiable {
    case top
    case afterCurrent
    case end

    var id: String { rawValue }

    var displayName: String {
        switch self {
        case .top:
            return String(localized: "workspace.placement.top", defaultValue: "Top")
        case .afterCurrent:
            return String(localized: "workspace.placement.afterCurrent", defaultValue: "After current")
        case .end:
            return String(localized: "workspace.placement.end", defaultValue: "End")
        }
    }

    var description: String {
        switch self {
        case .top:
            return String(
                localized: "workspace.placement.top.description",
                defaultValue: "Insert new workspaces at the top of the list."
            )
        case .afterCurrent:
            return String(
                localized: "workspace.placement.afterCurrent.description",
                defaultValue: "Insert new workspaces directly after the active workspace."
            )
        case .end:
            return String(
                localized: "workspace.placement.end.description",
                defaultValue: "Append new workspaces to the bottom of the list."
            )
        }
    }
}

enum WorkspaceAutoReorderSettings {
    static let key = "workspaceAutoReorderOnNotification"
    static let defaultValue = true

    static func isEnabled(defaults: UserDefaults = .standard) -> Bool {
        if defaults.object(forKey: key) == nil {
            return defaultValue
        }
        return defaults.bool(forKey: key)
    }
}

enum LastSurfaceCloseShortcutSettings {
    static let key = "closeWorkspaceOnLastSurfaceShortcut"
    // Keep the legacy stored meaning so existing values still map to the same
    // behavior. The default is flipped to preserve current Cmd+W behavior.
    static let defaultValue = true

    static func closesWorkspace(defaults: UserDefaults = .standard) -> Bool {
        if defaults.object(forKey: key) == nil {
            return defaultValue
        }
        return defaults.bool(forKey: key)
    }
}

enum SidebarBranchLayoutSettings {
    static let key = "sidebarBranchVerticalLayout"
    static let defaultVerticalLayout = true

    static func usesVerticalLayout(defaults: UserDefaults = .standard) -> Bool {
        if defaults.object(forKey: key) == nil {
            return defaultVerticalLayout
        }
        return defaults.bool(forKey: key)
    }
}

enum SidebarWorkspaceDetailSettings {
    static let hideAllDetailsKey = "sidebarHideAllDetails"
    static let showNotificationMessageKey = "sidebarShowNotificationMessage"
    static let defaultHideAllDetails = false
    static let defaultShowNotificationMessage = true

    static func hidesAllDetails(defaults: UserDefaults = .standard) -> Bool {
        if defaults.object(forKey: hideAllDetailsKey) == nil {
            return defaultHideAllDetails
        }
        return defaults.bool(forKey: hideAllDetailsKey)
    }

    static func showsNotificationMessage(defaults: UserDefaults = .standard) -> Bool {
        if defaults.object(forKey: showNotificationMessageKey) == nil {
            return defaultShowNotificationMessage
        }
        return defaults.bool(forKey: showNotificationMessageKey)
    }

    static func resolvedNotificationMessageVisibility(
        showNotificationMessage: Bool,
        hideAllDetails: Bool
    ) -> Bool {
        showNotificationMessage && !hideAllDetails
    }
}

struct SidebarWorkspaceAuxiliaryDetailVisibility: Equatable {
    let showsMetadata: Bool
    let showsLog: Bool
    let showsProgress: Bool
    let showsBranchDirectory: Bool
    let showsPullRequests: Bool
    let showsPorts: Bool

    static let hidden = Self(
        showsMetadata: false,
        showsLog: false,
        showsProgress: false,
        showsBranchDirectory: false,
        showsPullRequests: false,
        showsPorts: false
    )

    static func resolved(
        showMetadata: Bool,
        showLog: Bool,
        showProgress: Bool,
        showBranchDirectory: Bool,
        showPullRequests: Bool,
        showPorts: Bool,
        hideAllDetails: Bool
    ) -> Self {
        guard !hideAllDetails else { return .hidden }
        return Self(
            showsMetadata: showMetadata,
            showsLog: showLog,
            showsProgress: showProgress,
            showsBranchDirectory: showBranchDirectory,
            showsPullRequests: showPullRequests,
            showsPorts: showPorts
        )
    }
}

enum SidebarActiveTabIndicatorStyle: String, CaseIterable, Identifiable {
    case leftRail
    case solidFill

    var id: String { rawValue }

    var displayName: String {
        switch self {
        case .leftRail:
            return String(localized: "sidebar.activeTabIndicator.leftRail", defaultValue: "Left Rail")
        case .solidFill:
            return String(localized: "sidebar.activeTabIndicator.solidFill", defaultValue: "Solid Fill")
        }
    }
}

enum SidebarActiveTabIndicatorSettings {
    static let styleKey = "sidebarActiveTabIndicatorStyle"
    static let defaultStyle: SidebarActiveTabIndicatorStyle = .leftRail

    static func resolvedStyle(rawValue: String?) -> SidebarActiveTabIndicatorStyle {
        guard let rawValue else { return defaultStyle }
        if let style = SidebarActiveTabIndicatorStyle(rawValue: rawValue) {
            return style
        }

        // Legacy values from earlier iterations map to the closest modern option.
        switch rawValue {
        case "rail":
            return .leftRail
        case "border", "wash", "lift", "typography", "washRail", "blueWashColorRail":
            return .solidFill
        default:
            return defaultStyle
        }
    }

    static func current(defaults: UserDefaults = .standard) -> SidebarActiveTabIndicatorStyle {
        resolvedStyle(rawValue: defaults.string(forKey: styleKey))
    }
}

enum WorkspacePlacementSettings {
    static let placementKey = "newWorkspacePlacement"
    static let defaultPlacement: NewWorkspacePlacement = .afterCurrent

    static func current(defaults: UserDefaults = .standard) -> NewWorkspacePlacement {
        guard let raw = defaults.string(forKey: placementKey),
              let placement = NewWorkspacePlacement(rawValue: raw) else {
            return defaultPlacement
        }
        return placement
    }

    static func insertionIndex(
        placement: NewWorkspacePlacement,
        selectedIndex: Int?,
        selectedIsPinned: Bool,
        pinnedCount: Int,
        totalCount: Int
    ) -> Int {
        let clampedTotalCount = max(0, totalCount)
        let clampedPinnedCount = max(0, min(pinnedCount, clampedTotalCount))

        switch placement {
        case .top:
            // Keep pinned workspaces grouped at the top by inserting ahead of unpinned items.
            return clampedPinnedCount
        case .end:
            return clampedTotalCount
        case .afterCurrent:
            guard let selectedIndex, clampedTotalCount > 0 else {
                return clampedTotalCount
            }
            let clampedSelectedIndex = max(0, min(selectedIndex, clampedTotalCount - 1))
            if selectedIsPinned {
                return clampedPinnedCount
            }
            return min(clampedSelectedIndex + 1, clampedTotalCount)
        }
    }
}

struct WorkspaceTabColorEntry: Equatable, Identifiable {
    let name: String
    let hex: String

    var id: String { "\(name)-\(hex)" }
}

enum WorkspaceTabColorSettings {
    static let defaultOverridesKey = "workspaceTabColor.defaultOverrides"
    static let customColorsKey = "workspaceTabColor.customColors"
    static let maxCustomColors = 24

    private static let originalPRPalette: [WorkspaceTabColorEntry] = [
        WorkspaceTabColorEntry(name: "Red", hex: "#C0392B"),
        WorkspaceTabColorEntry(name: "Crimson", hex: "#922B21"),
        WorkspaceTabColorEntry(name: "Orange", hex: "#A04000"),
        WorkspaceTabColorEntry(name: "Amber", hex: "#7D6608"),
        WorkspaceTabColorEntry(name: "Olive", hex: "#4A5C18"),
        WorkspaceTabColorEntry(name: "Green", hex: "#196F3D"),
        WorkspaceTabColorEntry(name: "Teal", hex: "#006B6B"),
        WorkspaceTabColorEntry(name: "Aqua", hex: "#0E6B8C"),
        WorkspaceTabColorEntry(name: "Blue", hex: "#1565C0"),
        WorkspaceTabColorEntry(name: "Navy", hex: "#1A5276"),
        WorkspaceTabColorEntry(name: "Indigo", hex: "#283593"),
        WorkspaceTabColorEntry(name: "Purple", hex: "#6A1B9A"),
        WorkspaceTabColorEntry(name: "Magenta", hex: "#AD1457"),
        WorkspaceTabColorEntry(name: "Rose", hex: "#880E4F"),
        WorkspaceTabColorEntry(name: "Brown", hex: "#7B3F00"),
        WorkspaceTabColorEntry(name: "Charcoal", hex: "#3E4B5E"),
    ]

    static var defaultPalette: [WorkspaceTabColorEntry] {
        originalPRPalette
    }

    static func palette(defaults: UserDefaults = .standard) -> [WorkspaceTabColorEntry] {
        defaultPaletteWithOverrides(defaults: defaults) + customColorEntries(defaults: defaults)
    }

    static func defaultPaletteWithOverrides(defaults: UserDefaults = .standard) -> [WorkspaceTabColorEntry] {
        let palette = defaultPalette
        let overrides = defaultOverrideMap(defaults: defaults)
        return palette.map { entry in
            WorkspaceTabColorEntry(name: entry.name, hex: overrides[entry.name] ?? entry.hex)
        }
    }

    static func defaultColorHex(named name: String, defaults: UserDefaults = .standard) -> String {
        let palette = defaultPalette
        guard let entry = palette.first(where: { $0.name == name }) else {
            return palette.first?.hex ?? "#1565C0"
        }
        return defaultOverrideMap(defaults: defaults)[name] ?? entry.hex
    }

    static func setDefaultColor(named name: String, hex: String, defaults: UserDefaults = .standard) {
        let palette = defaultPalette
        guard let entry = palette.first(where: { $0.name == name }),
              let normalized = normalizedHex(hex) else { return }

        var overrides = defaultOverrideMap(defaults: defaults)
        if normalized == entry.hex {
            overrides.removeValue(forKey: name)
        } else {
            overrides[name] = normalized
        }
        saveDefaultOverrideMap(overrides, defaults: defaults)
    }

    static func customColors(defaults: UserDefaults = .standard) -> [String] {
        guard let raw = defaults.array(forKey: customColorsKey) as? [String] else { return [] }
        var result: [String] = []
        var seen: Set<String> = []
        for value in raw {
            guard let normalized = normalizedHex(value), seen.insert(normalized).inserted else { continue }
            result.append(normalized)
            if result.count >= maxCustomColors { break }
        }
        return result
    }

    static func customColorEntries(defaults: UserDefaults = .standard) -> [WorkspaceTabColorEntry] {
        customColors(defaults: defaults).enumerated().map { index, hex in
            WorkspaceTabColorEntry(name: "Custom \(index + 1)", hex: hex)
        }
    }

    @discardableResult
    static func addCustomColor(_ hex: String, defaults: UserDefaults = .standard) -> String? {
        guard let normalized = normalizedHex(hex) else { return nil }
        var colors = customColors(defaults: defaults)
        colors.removeAll { $0 == normalized }
        colors.insert(normalized, at: 0)
        setCustomColors(colors, defaults: defaults)
        return normalized
    }

    static func removeCustomColor(_ hex: String, defaults: UserDefaults = .standard) {
        guard let normalized = normalizedHex(hex) else { return }
        var colors = customColors(defaults: defaults)
        colors.removeAll { $0 == normalized }
        setCustomColors(colors, defaults: defaults)
    }

    static func setCustomColors(_ hexes: [String], defaults: UserDefaults = .standard) {
        var normalizedColors: [String] = []
        var seen: Set<String> = []
        for value in hexes {
            guard let normalized = normalizedHex(value), seen.insert(normalized).inserted else { continue }
            normalizedColors.append(normalized)
            if normalizedColors.count >= maxCustomColors { break }
        }

        if normalizedColors.isEmpty {
            defaults.removeObject(forKey: customColorsKey)
        } else {
            defaults.set(normalizedColors, forKey: customColorsKey)
        }
    }

    static func reset(defaults: UserDefaults = .standard) {
        defaults.removeObject(forKey: defaultOverridesKey)
        defaults.removeObject(forKey: customColorsKey)
    }

    static func normalizedHex(_ raw: String) -> String? {
        let trimmed = raw.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !trimmed.isEmpty else { return nil }
        let body = trimmed.hasPrefix("#") ? String(trimmed.dropFirst()) : trimmed
        guard body.count == 6 else { return nil }
        guard UInt64(body, radix: 16) != nil else { return nil }
        return "#" + body.uppercased()
    }

    static func displayColor(
        hex: String,
        colorScheme: ColorScheme,
        forceBright: Bool = false
    ) -> Color? {
        guard let color = displayNSColor(hex: hex, colorScheme: colorScheme, forceBright: forceBright) else {
            return nil
        }
        return Color(nsColor: color)
    }

    static func displayNSColor(
        hex: String,
        colorScheme: ColorScheme,
        forceBright: Bool = false
    ) -> NSColor? {
        guard let normalized = normalizedHex(hex),
              let baseColor = NSColor(hex: normalized) else {
            return nil
        }

        if forceBright || colorScheme == .dark {
            return brightenedForDarkAppearance(baseColor)
        }
        return baseColor
    }

    private static func defaultOverrideMap(defaults: UserDefaults) -> [String: String] {
        guard let raw = defaults.dictionary(forKey: defaultOverridesKey) as? [String: String] else { return [:] }
        let validNames = Set(defaultPalette.map(\.name))
        var normalized: [String: String] = [:]
        for (name, hex) in raw {
            guard validNames.contains(name),
                  let normalizedHex = normalizedHex(hex) else { continue }
            normalized[name] = normalizedHex
        }
        return normalized
    }

    private static func saveDefaultOverrideMap(_ map: [String: String], defaults: UserDefaults) {
        if map.isEmpty {
            defaults.removeObject(forKey: defaultOverridesKey)
        } else {
            defaults.set(map, forKey: defaultOverridesKey)
        }
    }

    private static func brightenedForDarkAppearance(_ color: NSColor) -> NSColor {
        let rgbColor = color.usingColorSpace(.sRGB) ?? color
        var hue: CGFloat = 0
        var saturation: CGFloat = 0
        var brightness: CGFloat = 0
        var alpha: CGFloat = 0
        rgbColor.getHue(&hue, saturation: &saturation, brightness: &brightness, alpha: &alpha)

        let boostedBrightness = min(1, max(brightness, 0.62) + ((1 - brightness) * 0.28))
        // Preserve neutral grays when brightening to avoid introducing hue shifts.
        let boostedSaturation: CGFloat
        if saturation <= 0.08 {
            boostedSaturation = saturation
        } else {
            boostedSaturation = min(1, saturation + ((1 - saturation) * 0.12))
        }

        return NSColor(
            hue: hue,
            saturation: boostedSaturation,
            brightness: boostedBrightness,
            alpha: alpha
        )
    }
}

/// Coalesces repeated main-thread signals into one callback after a short delay.
/// Useful for notification storms where only the latest update matters.
final class NotificationBurstCoalescer {
    private let delay: TimeInterval
    private var isFlushScheduled = false
    private var pendingAction: (() -> Void)?

    init(delay: TimeInterval = 1.0 / 30.0) {
        self.delay = max(0, delay)
    }

    func signal(_ action: @escaping () -> Void) {
        precondition(Thread.isMainThread, "NotificationBurstCoalescer must be used on the main thread")
        pendingAction = action
        scheduleFlushIfNeeded()
    }

    private func scheduleFlushIfNeeded() {
        guard !isFlushScheduled else { return }
        isFlushScheduled = true
        DispatchQueue.main.asyncAfter(deadline: .now() + delay) { [weak self] in
            self?.flush()
        }
    }

    private func flush() {
        precondition(Thread.isMainThread, "NotificationBurstCoalescer must be used on the main thread")
        isFlushScheduled = false
        guard let action = pendingAction else { return }
        pendingAction = nil
        action()
        if pendingAction != nil {
            scheduleFlushIfNeeded()
        }
    }
}

struct RecentlyClosedBrowserStack {
    private(set) var entries: [ClosedBrowserPanelRestoreSnapshot] = []
    let capacity: Int

    init(capacity: Int) {
        self.capacity = max(1, capacity)
    }

    var isEmpty: Bool {
        entries.isEmpty
    }

    mutating func push(_ snapshot: ClosedBrowserPanelRestoreSnapshot) {
        entries.append(snapshot)
        if entries.count > capacity {
            entries.removeFirst(entries.count - capacity)
        }
    }

    mutating func pop() -> ClosedBrowserPanelRestoreSnapshot? {
        entries.popLast()
    }
}

#if DEBUG
// Sample the actual IOSurface-backed terminal layer at vsync cadence so UI tests can reliably
// catch a single compositor-frame blank flash and any transient compositor scaling (stretched text).
//
// This is DEBUG-only and used only for UI tests; no polling or display-link loops exist in normal app runtime.
fileprivate final class VsyncIOSurfaceTimelineState {
    struct Target {
        let label: String
        let sample: @MainActor () -> GhosttySurfaceScrollView.DebugFrameSample?
    }

    let frameCount: Int
    let closeFrame: Int
    let lock = NSLock()

    var framesWritten = 0
    var inFlight = false
    var finished = false

    var scheduledActions: [(frame: Int, action: () -> Void)] = []
    var nextActionIndex: Int = 0

    var targets: [Target] = []

    // Results
    var firstBlank: (label: String, frame: Int)?
    var firstSizeMismatch: (label: String, frame: Int, ios: String, expected: String)?
    var trace: [String] = []

    var link: CVDisplayLink?
    var continuation: CheckedContinuation<Void, Never>?

    init(frameCount: Int, closeFrame: Int) {
        self.frameCount = frameCount
        self.closeFrame = closeFrame
    }

    func tryBeginCapture() -> Bool {
        lock.lock()
        defer { lock.unlock() }
        if finished { return false }
        if inFlight { return false }
        inFlight = true
        return true
    }

    func endCapture() {
        lock.lock()
        inFlight = false
        lock.unlock()
    }

    func finish() {
        lock.lock()
        if finished {
            lock.unlock()
            return
        }
        finished = true
        let cont = continuation
        continuation = nil
        lock.unlock()
        cont?.resume()
    }
}

fileprivate func cmuxVsyncIOSurfaceTimelineCallback(
    _ displayLink: CVDisplayLink,
    _ inNow: UnsafePointer<CVTimeStamp>,
    _ inOutputTime: UnsafePointer<CVTimeStamp>,
    _ flagsIn: CVOptionFlags,
    _ flagsOut: UnsafeMutablePointer<CVOptionFlags>,
    _ ctx: UnsafeMutableRawPointer?
) -> CVReturn {
    guard let ctx else { return kCVReturnSuccess }
    let st = Unmanaged<VsyncIOSurfaceTimelineState>.fromOpaque(ctx).takeUnretainedValue()
    if !st.tryBeginCapture() { return kCVReturnSuccess }

    // Sample on the main thread synchronously so we don't "miss" a single compositor frame.
    // (The previous Task/@MainActor hop could be delayed long enough to skip the blank frame.)
    DispatchQueue.main.sync {
        defer { st.endCapture() }
        guard st.framesWritten < st.frameCount else { return }

        while st.nextActionIndex < st.scheduledActions.count {
            let next = st.scheduledActions[st.nextActionIndex]
            if next.frame != st.framesWritten { break }
            st.nextActionIndex += 1
            next.action()
        }

        for t in st.targets {
            guard let s = t.sample() else { continue }

            let iosW = s.iosurfaceWidthPx
            let iosH = s.iosurfaceHeightPx
            let expW = s.expectedWidthPx
            let expH = s.expectedHeightPx
            let gravity = s.layerContentsGravity
            let hasDimensions = iosW > 0 && iosH > 0 && expW > 0 && expH > 0
            let dw = hasDimensions ? abs(iosW - expW) : 0
            let dh = hasDimensions ? abs(iosH - expH) : 0
            let hasSizeMismatch = hasDimensions && (dw > 2 || dh > 2)
            let stretchRisk = (gravity == CALayerContentsGravity.resize.rawValue)

            // Ignore setup/warmup frames before the close action. We only care about
            // regressions that happen at/after the close mutation.
            if st.firstBlank == nil, st.framesWritten >= st.closeFrame, s.isProbablyBlank {
                st.firstBlank = (label: t.label, frame: st.framesWritten)
            }

            if st.firstSizeMismatch == nil,
               st.framesWritten >= st.closeFrame,
               stretchRisk,
               hasSizeMismatch {
                st.firstSizeMismatch = (
                    label: t.label,
                    frame: st.framesWritten,
                    ios: "\(iosW)x\(iosH)",
                    expected: "\(expW)x\(expH)"
                )
            }

            if st.trace.count < 200 {
                st.trace.append("\(st.framesWritten):\(t.label):blank=\(s.isProbablyBlank ? 1 : 0):ios=\(iosW)x\(iosH):exp=\(expW)x\(expH):gravity=\(gravity):key=\(s.layerContentsKey)")
            }
        }

        st.framesWritten += 1
    }

    // Stop/resume outside the main-thread sync block to avoid reentrancy issues.
    if st.framesWritten >= st.frameCount, let link = st.link {
        CVDisplayLinkStop(link)
        st.finish()
        Unmanaged<VsyncIOSurfaceTimelineState>.fromOpaque(ctx).release()
    }

    return kCVReturnSuccess
}
#endif

@MainActor
class TabManager: ObservableObject {
    private enum WorkspacePullRequestSnapshot: Equatable {
        case unsupportedRepository
        case notFound
        case resolved(SidebarPullRequestState)
        case transientFailure
    }

    private struct InitialWorkspaceGitMetadataSnapshot: Equatable {
        let branch: String?
        let isDirty: Bool
        let pullRequest: WorkspacePullRequestSnapshot
    }

    private struct CommandResult {
        let stdout: String?
        let stderr: String?
        let exitStatus: Int32?
        let timedOut: Bool
        let executionError: String?
    }

    private struct WorkspaceGitProbeKey: Hashable {
        let workspaceId: UUID
        let panelId: UUID
    }

    struct GitHubPullRequestProbeItem: Decodable, Equatable {
        let number: Int
        let state: String
        let url: String
        let updatedAt: String?
    }

    private struct GitHubPullRequestCheckItem: Decodable {
        let bucket: String?
        let state: String?
    }

    /// The window that owns this TabManager. Set by AppDelegate.registerMainWindow().
    /// Used to apply title updates to the correct window instead of NSApp.keyWindow.
    weak var window: NSWindow?

    @Published var tabs: [Workspace] = []
    @Published private(set) var isWorkspaceCycleHot: Bool = false
    @Published private(set) var pendingBackgroundWorkspaceLoadIds: Set<UUID> = []
    @Published private(set) var debugPinnedWorkspaceLoadIds: Set<UUID> = []

    /// Global monotonically increasing counter for CMUX_PORT ordinal assignment.
    /// Static so port ranges don't overlap across multiple windows (each window has its own TabManager).
    private static var nextPortOrdinal: Int = 0
    private static let initialWorkspaceGitProbeDelays: [TimeInterval] = [0, 0.5, 1.5, 3.0, 6.0, 10.0]
    private static let workspaceGitMetadataPollInterval: TimeInterval = 30
    private static let selectedWorkspaceGitMetadataPollInterval: TimeInterval = 5
    private nonisolated static let workspacePullRequestProbeTimeout: TimeInterval = 5.0
    @Published var selectedTabId: UUID? {
        willSet {
#if DEBUG
            guard newValue != selectedTabId else {
                debugPendingWorkspaceSwitchTrigger = nil
                debugPendingWorkspaceSwitchTarget = nil
                debugPreparedWorkspaceSwitchTarget = nil
                return
            }

            if debugPreparedWorkspaceSwitchTarget == newValue {
                debugPreparedWorkspaceSwitchTarget = nil
                debugPendingWorkspaceSwitchTrigger = nil
                debugPendingWorkspaceSwitchTarget = nil
            } else {
                let trigger = (debugPendingWorkspaceSwitchTarget == newValue
                    ? debugPendingWorkspaceSwitchTrigger
                    : nil) ?? "direct"
                debugPendingWorkspaceSwitchTrigger = nil
                debugPendingWorkspaceSwitchTarget = nil
                debugBeginWorkspaceSwitch(
                    trigger: trigger,
                    from: selectedTabId,
                    to: newValue
                )
            }
#endif
        }
        didSet {
            guard selectedTabId != oldValue else { return }
            sentryBreadcrumb("workspace.switch", data: [
                "tabCount": tabs.count
            ])
            let previousTabId = oldValue
            if let previousTabId,
               let previousPanelId = focusedPanelId(for: previousTabId) {
                lastFocusedPanelByTab[previousTabId] = previousPanelId
            }
            if !isNavigatingHistory, let selectedTabId {
                recordTabInHistory(selectedTabId)
            }
#if DEBUG
            let switchId = debugWorkspaceSwitchId
            let switchDtMs = debugWorkspaceSwitchStartTime > 0
                ? (CACurrentMediaTime() - debugWorkspaceSwitchStartTime) * 1000
                : 0
            dlog(
                "ws.select.didSet id=\(switchId) from=\(Self.debugShortWorkspaceId(previousTabId)) " +
                "to=\(Self.debugShortWorkspaceId(selectedTabId)) dt=\(Self.debugMsText(switchDtMs))"
            )
#endif
            selectionSideEffectsGeneration &+= 1
            let generation = selectionSideEffectsGeneration
            DispatchQueue.main.async { [weak self] in
                guard let self, self.selectionSideEffectsGeneration == generation else { return }
                self.focusSelectedTabPanel(previousTabId: previousTabId)
                self.updateWindowTitleForSelectedTab()
                if let selectedTabId = self.selectedTabId {
                    self.dismissFocusedPanelNotificationIfActive(tabId: selectedTabId)
                }
#if DEBUG
                let dtMs = self.debugWorkspaceSwitchStartTime > 0
                    ? (CACurrentMediaTime() - self.debugWorkspaceSwitchStartTime) * 1000
                    : 0
                dlog(
                    "ws.select.asyncDone id=\(self.debugWorkspaceSwitchId) dt=\(Self.debugMsText(dtMs)) " +
                    "selected=\(Self.debugShortWorkspaceId(self.selectedTabId))"
                )
#endif
            }
        }
    }
    private var observers: [NSObjectProtocol] = []
    private var suppressFocusFlash = false
    private var lastFocusedPanelByTab: [UUID: UUID] = [:]
    private struct PanelTitleUpdateKey: Hashable {
        let tabId: UUID
        let panelId: UUID
    }
    private var pendingPanelTitleUpdates: [PanelTitleUpdateKey: String] = [:]
    private let panelTitleUpdateCoalescer = NotificationBurstCoalescer(delay: 1.0 / 30.0)
    private var recentlyClosedBrowsers = RecentlyClosedBrowserStack(capacity: 20)
    private let initialWorkspaceGitProbeQueue = DispatchQueue(
        label: "com.cmux.initial-workspace-git-probe",
        qos: .utility
    )
    private var workspaceGitProbeGenerationByKey: [WorkspaceGitProbeKey: UUID] = [:]
    private var workspaceGitProbeTimersByKey: [WorkspaceGitProbeKey: [DispatchSourceTimer]] = [:]

    // Recent tab history for back/forward navigation (like browser history)
    private var tabHistory: [UUID] = []
    private var historyIndex: Int = -1
    private var isNavigatingHistory = false
    private let maxHistorySize = 50
    private var selectionSideEffectsGeneration: UInt64 = 0
    private var workspaceCycleGeneration: UInt64 = 0
    private var workspaceCycleCooldownTask: Task<Void, Never>?
    private var pendingWorkspaceUnfocusTarget: (tabId: UUID, panelId: UUID)?
    private var sidebarSelectedWorkspaceIds: Set<UUID> = []
    var confirmCloseHandler: ((String, String, Bool) -> Bool)?
    private struct WorkspaceCreationTabSnapshot {
        let id: UUID
        let isPinned: Bool

        @MainActor
        init(workspace: Workspace) {
            self.id = workspace.id
            self.isPinned = workspace.isPinned
        }
    }

    private struct WorkspaceCreationSnapshot {
        let tabs: [WorkspaceCreationTabSnapshot]
        let selectedTabId: UUID?
        let selectedTabWasPinned: Bool
        let preferredWorkingDirectory: String?
        let inheritedTerminalFontPoints: Float?
    }
    private var agentPIDSweepTimer: DispatchSourceTimer?
    private var workspaceGitMetadataPollTimer: DispatchSourceTimer?
    private var selectedWorkspaceGitMetadataPollTimer: DispatchSourceTimer?
#if DEBUG
    private var debugWorkspaceSwitchCounter: UInt64 = 0
    private var debugWorkspaceSwitchId: UInt64 = 0
    private var debugWorkspaceSwitchStartTime: CFTimeInterval = 0
    private var debugPendingWorkspaceSwitchTrigger: String?
    private var debugPendingWorkspaceSwitchTarget: UUID?
    private var debugPreparedWorkspaceSwitchTarget: UUID?
#endif

#if DEBUG
    private var didSetupSplitCloseRightUITest = false
    private var didSetupUITestFocusShortcuts = false
    private var didSetupChildExitSplitUITest = false
    private var didSetupChildExitKeyboardUITest = false
    private var uiTestCancellables = Set<AnyCancellable>()
#endif

    init(initialWorkingDirectory: String? = nil) {
        addWorkspace(workingDirectory: initialWorkingDirectory)
        observers.append(NotificationCenter.default.addObserver(
            forName: .ghosttyDidSetTitle,
            object: nil,
            queue: .main
        ) { [weak self] notification in
            MainActor.assumeIsolated { [weak self] in
                guard let self else { return }
                guard let tabId = notification.userInfo?[GhosttyNotificationKey.tabId] as? UUID else { return }
                guard let surfaceId = notification.userInfo?[GhosttyNotificationKey.surfaceId] as? UUID else { return }
                guard let title = notification.userInfo?[GhosttyNotificationKey.title] as? String else { return }
                enqueuePanelTitleUpdate(tabId: tabId, panelId: surfaceId, title: title)
            }
        })
        observers.append(NotificationCenter.default.addObserver(
            forName: .ghosttyDidFocusSurface,
            object: nil,
            queue: .main
        ) { [weak self] notification in
            MainActor.assumeIsolated { [weak self] in
                guard let self else { return }
                guard let tabId = notification.userInfo?[GhosttyNotificationKey.tabId] as? UUID else { return }
                guard let surfaceId = notification.userInfo?[GhosttyNotificationKey.surfaceId] as? UUID else { return }
                dismissPanelNotificationOnFocusIfActive(tabId: tabId, panelId: surfaceId)
            }
        })

        startAgentPIDSweepTimer()
        startWorkspaceGitMetadataPollTimer()
        startSelectedWorkspaceGitMetadataPollTimer()
#if DEBUG
        setupUITestFocusShortcutsIfNeeded()
        setupSplitCloseRightUITestIfNeeded()
        setupChildExitSplitUITestIfNeeded()
        setupChildExitKeyboardUITestIfNeeded()
#endif
    }

    deinit {
        workspaceCycleCooldownTask?.cancel()
        agentPIDSweepTimer?.cancel()
        workspaceGitMetadataPollTimer?.cancel()
        selectedWorkspaceGitMetadataPollTimer?.cancel()
    }

    // MARK: - Agent PID Sweep

    /// Periodically checks agent PIDs associated with status entries.
    /// If a process has exited (SIGKILL, crash, etc.), clears the stale status entry.
    /// This is the safety net for cases where no hook fires (e.g. SIGKILL).
    private func startAgentPIDSweepTimer() {
        let timer = DispatchSource.makeTimerSource(queue: .global(qos: .utility))
        timer.schedule(deadline: .now() + 30, repeating: 30)
        timer.setEventHandler { [weak self] in
            guard let self else { return }
            DispatchQueue.main.async { [weak self] in
                guard let self else { return }
                self.sweepStaleAgentPIDs()
            }
        }
        timer.resume()
        agentPIDSweepTimer = timer
    }

    /// Periodically refreshes git/PR metadata for tracked workspace branches so
    /// remote GitHub state changes (e.g. PR open -> merged) reach sidebar state
    /// even when the local branch/directory does not change.
    private func startWorkspaceGitMetadataPollTimer() {
        let timer = DispatchSource.makeTimerSource(queue: .global(qos: .utility))
        let interval = Self.workspaceGitMetadataPollInterval
        timer.schedule(deadline: .now() + interval, repeating: interval)
        timer.setEventHandler { [weak self] in
            guard let self else { return }
            DispatchQueue.main.async { [weak self] in
                guard let self else { return }
                self.refreshTrackedWorkspaceGitMetadata()
            }
        }
        timer.resume()
        workspaceGitMetadataPollTimer = timer
    }

    /// Refresh the selected workspace more aggressively so branch checkouts and
    /// newly created PRs show up in the sidebar without waiting for the slower
    /// background sweep across every tracked workspace.
    private func startSelectedWorkspaceGitMetadataPollTimer() {
        let timer = DispatchSource.makeTimerSource(queue: .global(qos: .utility))
        let interval = Self.selectedWorkspaceGitMetadataPollInterval
        timer.schedule(deadline: .now() + interval, repeating: interval)
        timer.setEventHandler { [weak self] in
            guard let self else { return }
            DispatchQueue.main.async { [weak self] in
                guard let self else { return }
                self.refreshSelectedWorkspaceGitMetadata()
            }
        }
        timer.resume()
        selectedWorkspaceGitMetadataPollTimer = timer
    }

    private func refreshTrackedWorkspaceGitMetadata() {
        let activeProbeKeys = Set(workspaceGitProbeGenerationByKey.keys)

        for workspace in tabs {
            for panelId in trackedWorkspaceGitMetadataPollCandidatePanelIds(
                in: workspace,
                activeProbeKeys: activeProbeKeys
            ) {
                scheduleWorkspaceGitMetadataRefreshIfPossible(
                    workspaceId: workspace.id,
                    panelId: panelId,
                    reason: "periodicPoll"
                )
            }
        }
    }

    private func refreshSelectedWorkspaceGitMetadata() {
        guard let workspace = selectedWorkspace,
              let focusedPanelId = workspace.focusedPanelId else {
            return
        }

        let activeProbeKeys = Set(workspaceGitProbeGenerationByKey.keys)
        let candidatePanelIds = trackedWorkspaceGitMetadataPollCandidatePanelIds(
            in: workspace,
            activeProbeKeys: activeProbeKeys
        )
        guard candidatePanelIds.contains(focusedPanelId) else { return }

        scheduleWorkspaceGitMetadataRefreshIfPossible(
            workspaceId: workspace.id,
            panelId: focusedPanelId,
            reason: "selectedPeriodicPoll"
        )
    }

    func refreshTrackedWorkspaceGitMetadataForTesting() {
        refreshTrackedWorkspaceGitMetadata()
    }

    func trackedWorkspaceGitMetadataPollCandidatePanelIdsForTesting(workspaceId: UUID) -> Set<UUID> {
        let activeProbeKeys = Set(workspaceGitProbeGenerationByKey.keys)
        guard let workspace = tabs.first(where: { $0.id == workspaceId }) else {
            return []
        }
        return trackedWorkspaceGitMetadataPollCandidatePanelIds(
            in: workspace,
            activeProbeKeys: activeProbeKeys
        )
    }

    private func trackedWorkspaceGitMetadataPollCandidatePanelIds(
        in workspace: Workspace,
        activeProbeKeys: Set<WorkspaceGitProbeKey>
    ) -> Set<UUID> {
        var candidatePanelIds = Set(workspace.panelGitBranches.keys)
        candidatePanelIds.formUnion(workspace.panelPullRequests.keys)

        if candidatePanelIds.isEmpty,
           let focusedPanelId = workspace.focusedPanelId,
           workspace.gitBranch != nil || workspace.pullRequest != nil {
            candidatePanelIds.insert(focusedPanelId)
        }

        return Set(candidatePanelIds.filter { panelId in
            let probeKey = WorkspaceGitProbeKey(workspaceId: workspace.id, panelId: panelId)
            return !activeProbeKeys.contains(probeKey)
        })
    }

    private func sweepStaleAgentPIDs() {
        for tab in tabs {
            var keysToRemove: [String] = []
            for (key, pid) in tab.agentPIDs {
                guard pid > 0 else {
                    keysToRemove.append(key)
                    continue
                }
                // kill(pid, 0) probes process liveness without sending a signal.
                // ESRCH = process doesn't exist (stale). EPERM = process exists
                // but we lack permission (not stale, keep tracking).
                errno = 0
                if kill(pid, 0) == -1, POSIXErrorCode(rawValue: errno) == .ESRCH {
                    keysToRemove.append(key)
                }
            }
            if !keysToRemove.isEmpty {
                for key in keysToRemove {
                    tab.statusEntries.removeValue(forKey: key)
                    tab.agentPIDs.removeValue(forKey: key)
                }
                // Also clear stale notifications (e.g. "Doing well, thanks!")
                // left behind when Claude was killed without SessionEnd firing.
                AppDelegate.shared?.notificationStore?.clearNotifications(forTabId: tab.id)
            }
        }
    }

    private func gitProbeDirectory(for workspace: Workspace, panelId: UUID) -> String? {
        let rawDirectory = workspace.panelDirectories[panelId]
            ?? (workspace.focusedPanelId == panelId ? workspace.currentDirectory : nil)
        return rawDirectory.flatMap(normalizedWorkingDirectory)
    }

    private func scheduleWorkspaceGitMetadataRefreshIfPossible(
        workspaceId: UUID,
        panelId: UUID,
        reason: String,
        delays: [TimeInterval] = [0]
    ) {
        guard let workspace = tabs.first(where: { $0.id == workspaceId }),
              workspace.panels[panelId] != nil,
              let directory = gitProbeDirectory(for: workspace, panelId: panelId) else {
            return
        }

        scheduleWorkspaceGitMetadataRefresh(
            workspaceId: workspaceId,
            panelId: panelId,
            directory: directory,
            delays: delays,
            reason: reason
        )
    }

    private func wireClosedBrowserTracking(for workspace: Workspace) {
        workspace.onClosedBrowserPanel = { [weak self] snapshot in
            self?.recentlyClosedBrowsers.push(snapshot)
        }
    }

    private func unwireClosedBrowserTracking(for workspace: Workspace) {
        workspace.onClosedBrowserPanel = nil
    }

    var selectedWorkspace: Workspace? {
        guard let selectedTabId else { return nil }
        return tabs.first(where: { $0.id == selectedTabId })
    }

    // Keep selectedTab as convenience alias
    var selectedTab: Workspace? { selectedWorkspace }

    // MARK: - Surface/Panel Compatibility Layer

    /// Returns the focused terminal surface for the selected workspace
    var selectedSurface: TerminalSurface? {
        selectedWorkspace?.focusedTerminalPanel?.surface
    }

    /// Returns the focused panel's terminal panel (if it is a terminal)
    var selectedTerminalPanel: TerminalPanel? {
        selectedWorkspace?.focusedTerminalPanel
    }

    var isFindVisible: Bool {
        selectedTerminalPanel?.searchState != nil || focusedBrowserPanel?.searchState != nil
    }

    var canUseSelectionForFind: Bool {
        selectedTerminalPanel?.hasSelection() == true
    }

    func startSearch() {
        if let panel = selectedTerminalPanel {
            if panel.searchState == nil {
                panel.searchState = TerminalSurface.SearchState()
            }
            NSLog("Find: startSearch workspace=%@ panel=%@", panel.workspaceId.uuidString, panel.id.uuidString)
            NotificationCenter.default.post(name: .ghosttySearchFocus, object: panel.surface)
            _ = panel.performBindingAction("start_search")
            return
        }
        if let panel = selectedTerminalPanel {
            let hadExistingSearch = panel.searchState != nil
            let handled = startOrFocusTerminalSearch(panel.surface)
            NSLog("Find: startSearch workspace=%@ panel=%@", panel.workspaceId.uuidString, panel.id.uuidString)
#if DEBUG
            dlog(
                "find.startSearch workspace=\(panel.workspaceId.uuidString.prefix(5)) " +
                "panel=\(panel.id.uuidString.prefix(5)) existing=\(hadExistingSearch ? "yes" : "no") " +
                "handled=\(handled ? 1 : 0) " +
                "firstResponder=\(String(describing: panel.surface.hostedView.window?.firstResponder))"
            )
#endif
            return
        }

        focusedBrowserPanel?.startFind()
    }

    func searchSelection() {
        guard let panel = selectedTerminalPanel else { return }
        if panel.searchState == nil {
            panel.searchState = TerminalSurface.SearchState()
        }
        NSLog("Find: searchSelection workspace=%@ panel=%@", panel.workspaceId.uuidString, panel.id.uuidString)
        NotificationCenter.default.post(name: .ghosttySearchFocus, object: panel.surface)
        _ = panel.performBindingAction("search_selection")
    }

    func findNext() {
        if let panel = selectedTerminalPanel {
            _ = panel.performBindingAction("search:next")
            return
        }

        focusedBrowserPanel?.findNext()
    }

    func findPrevious() {
        if let panel = selectedTerminalPanel {
            _ = panel.performBindingAction("search:previous")
            return
        }

        focusedBrowserPanel?.findPrevious()
    }

    @discardableResult
    func toggleFocusedTerminalCopyMode() -> Bool {
        guard let panel = selectedTerminalPanel else { return false }
        return panel.surface.toggleKeyboardCopyMode()
    }

    func hideFind() {
        if let panel = selectedTerminalPanel {
            panel.searchState = nil
            return
        }

        focusedBrowserPanel?.hideFind()
    }

    func makeWorkspaceForCreation(
        title: String,
        workingDirectory: String?,
        portOrdinal: Int,
        configTemplate: CmuxSurfaceConfigTemplate?,
        initialTerminalCommand: String?,
        initialTerminalEnvironment: [String: String]
    ) -> Workspace {
        Workspace(
            title: title,
            workingDirectory: workingDirectory,
            portOrdinal: portOrdinal,
            configTemplate: configTemplate,
            initialTerminalCommand: initialTerminalCommand,
            initialTerminalEnvironment: initialTerminalEnvironment
        )
    }

    /// Test seam for mutating live workspace state after the creation snapshot is captured.
    func didCaptureWorkspaceCreationSnapshot() {}

#if DEBUG
    private func maybeMutateSelectionDuringWorkspaceCreationForDev(
        snapshot: WorkspaceCreationSnapshot
    ) {
        let env = ProcessInfo.processInfo.environment
        let isEnabled: Bool = {
            if let raw = env["CMUX_DEV_MUTATE_WORKSPACE_SELECTION_DURING_CREATION"] {
                return raw == "1" || raw.caseInsensitiveCompare("true") == .orderedSame
            }
            return UserDefaults.standard.bool(forKey: "cmuxDevMutateWorkspaceSelectionDuringCreation")
        }()
        guard isEnabled,
              let selectedTabId = snapshot.selectedTabId,
              let targetId = snapshot.tabs.lazy.map(\.id).first(where: { $0 != selectedTabId }),
              tabs.contains(where: { $0.id == targetId }) else {
            return
        }
        dlog(
            "workspace.create.devSelectionMutation from=\(selectedTabId.uuidString.prefix(5)) " +
            "to=\(targetId.uuidString.prefix(5))"
        )
        self.selectedTabId = targetId
    }
#endif

    @discardableResult
    func addWorkspace(
        title: String? = nil,
        workingDirectory overrideWorkingDirectory: String? = nil,
        initialTerminalCommand: String? = nil,
        initialTerminalEnvironment: [String: String] = [:],
        select: Bool = true,
        eagerLoadTerminal: Bool = false,
        placementOverride: NewWorkspacePlacement? = nil,
        autoWelcomeIfNeeded: Bool = true
    ) -> Workspace {
        let sourceWorkspace = selectedWorkspace
        let capturedTabs = tabs
        // Snapshot the selected tab from the pinned workspace instead of rereading the
        // @Published selectedTabId storage after the inheritance helpers. The arm64 Nightly
        // Cmd+N crash is in PublishedSubject.value.getter on that second getter read.
        let capturedSelectedTabId = sourceWorkspace?.id
        // Keep both the source workspace and the pre-creation workspace array alive for the
        // entire creation path. Release ARC can otherwise drop retains early across the
        // helper/insertion chain, which reintroduces use-after-free crashes in optimized builds.
        return withExtendedLifetime((capturedTabs, sourceWorkspace)) {
            let dir = preferredWorkingDirectoryForNewTab(workspace: sourceWorkspace)
            let font = inheritedTerminalFontPointsForNewWorkspace(workspace: sourceWorkspace)
            let snapshot = workspaceCreationSnapshotLite(
                currentTabs: capturedTabs,
                currentSelectedTabId: capturedSelectedTabId,
                preferredWorkingDirectory: dir,
                inheritedTerminalFontPoints: font
            )
            didCaptureWorkspaceCreationSnapshot()
#if DEBUG
            maybeMutateSelectionDuringWorkspaceCreationForDev(snapshot: snapshot)
#endif
            let nextTabCount = snapshot.tabs.count + 1
            sentryBreadcrumb("workspace.create", data: ["tabCount": nextTabCount])
            let explicitWorkingDirectory = normalizedWorkingDirectory(overrideWorkingDirectory)
            let workingDirectory = explicitWorkingDirectory ?? snapshot.preferredWorkingDirectory
            let inheritedConfig = workspaceCreationConfigTemplate(
                inheritedTerminalFontPoints: snapshot.inheritedTerminalFontPoints
            )
            // Resolve placement against the pre-creation snapshot before Workspace init
            // boots terminal state. The ssh/new-workspace path can otherwise crash while
            // reading @Published placement state from existing workspaces mid-creation.
            let insertIndex = newTabInsertIndex(snapshot: snapshot, placementOverride: placementOverride)
            let ordinal = Self.nextPortOrdinal
            Self.nextPortOrdinal += 1
            let newWorkspace = makeWorkspaceForCreation(
                title: title ?? "Terminal \(nextTabCount)",
                workingDirectory: workingDirectory,
                portOrdinal: ordinal,
                configTemplate: inheritedConfig,
                initialTerminalCommand: initialTerminalCommand,
                initialTerminalEnvironment: initialTerminalEnvironment
            )
            newWorkspace.owningTabManager = self
            if title != nil {
                newWorkspace.setCustomTitle(title)
            }
            wireClosedBrowserTracking(for: newWorkspace)
            if eagerLoadTerminal && !select {
                requestBackgroundWorkspaceLoad(for: newWorkspace.id)
            }
            // Apply insertion to the current live array so post-snapshot closes/reorders
            // are preserved instead of reintroducing stale workspace instances.
            var updatedTabs = tabs
            if insertIndex >= 0 && insertIndex <= updatedTabs.count {
                updatedTabs.insert(newWorkspace, at: insertIndex)
            } else {
                updatedTabs.append(newWorkspace)
            }
            tabs = updatedTabs
            if let explicitWorkingDirectory,
               let terminalPanel = newWorkspace.focusedTerminalPanel {
                scheduleInitialWorkspaceGitMetadataRefresh(
                    workspaceId: newWorkspace.id,
                    panelId: terminalPanel.id,
                    directory: explicitWorkingDirectory
                )
            }
            if eagerLoadTerminal {
                if select {
                    newWorkspace.focusedTerminalPanel?.surface.requestBackgroundSurfaceStartIfNeeded()
                }
            }
            if select {
#if DEBUG
                debugPrimeWorkspaceSwitchTrigger("create", to: newWorkspace.id)
#endif
                selectedTabId = newWorkspace.id
                NotificationCenter.default.post(
                    name: .ghosttyDidFocusTab,
                    object: nil,
                    userInfo: [GhosttyNotificationKey.tabId: newWorkspace.id]
                )
            }
#if DEBUG
            UITestRecorder.incrementInt("addTabInvocations")
            UITestRecorder.record([
                "tabCount": String(updatedTabs.count),
                "selectedTabId": select ? newWorkspace.id.uuidString : (snapshot.selectedTabId?.uuidString ?? "")
            ])
#endif
            if autoWelcomeIfNeeded && select && !UserDefaults.standard.bool(forKey: WelcomeSettings.shownKey) {
                if let appDelegate = AppDelegate.shared {
                    appDelegate.sendWelcomeCommandWhenReady(to: newWorkspace, markShownOnSend: true)
                } else {
                    sendWelcomeWhenReady(to: newWorkspace)
                }
            }
            return newWorkspace
        }
    }

    @MainActor
    private func sendWelcomeWhenReady(to workspace: Workspace) {
        if let terminalPanel = workspace.focusedTerminalPanel,
           terminalPanel.surface.surface != nil {
            DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
                UserDefaults.standard.set(true, forKey: WelcomeSettings.shownKey)
                terminalPanel.sendText("cmux welcome\n")
            }
            return
        }

        var resolved = false
        var readyObserver: NSObjectProtocol?
        var panelsCancellable: AnyCancellable?

        func finishIfReady() {
            guard !resolved,
                  let terminalPanel = workspace.focusedTerminalPanel,
                  terminalPanel.surface.surface != nil else { return }
            resolved = true
            if let readyObserver {
                NotificationCenter.default.removeObserver(readyObserver)
            }
            panelsCancellable?.cancel()
            DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
                UserDefaults.standard.set(true, forKey: WelcomeSettings.shownKey)
                terminalPanel.sendText("cmux welcome\n")
            }
        }

        panelsCancellable = workspace.$panels
            .map { _ in () }
            .sink { _ in
                Task { @MainActor in
                    finishIfReady()
                }
            }
        readyObserver = NotificationCenter.default.addObserver(
            forName: .terminalSurfaceDidBecomeReady,
            object: nil,
            queue: .main
        ) { note in
            guard let workspaceId = note.userInfo?["workspaceId"] as? UUID,
                  workspaceId == workspace.id else { return }
            Task { @MainActor in
                finishIfReady()
            }
        }
        DispatchQueue.main.asyncAfter(deadline: .now() + 3.0) {
            Task { @MainActor in
                if let readyObserver, !resolved {
                    NotificationCenter.default.removeObserver(readyObserver)
                }
                if !resolved {
                    panelsCancellable?.cancel()
                }
            }
        }
    }

    private func scheduleInitialWorkspaceGitMetadataRefresh(
        workspaceId: UUID,
        panelId: UUID,
        directory: String
    ) {
        scheduleWorkspaceGitMetadataRefresh(
            workspaceId: workspaceId,
            panelId: panelId,
            directory: directory,
            delays: Self.initialWorkspaceGitProbeDelays,
            reason: "initial"
        )
    }

    private func scheduleWorkspaceGitMetadataRefresh(
        workspaceId: UUID,
        panelId: UUID,
        directory: String,
        delays: [TimeInterval],
        reason: String
    ) {
        let normalizedDirectory = normalizeDirectory(directory)
        let key = WorkspaceGitProbeKey(workspaceId: workspaceId, panelId: panelId)
        let generation = UUID()
        cancelWorkspaceGitProbeTimers(for: key)
        workspaceGitProbeGenerationByKey[key] = generation

#if DEBUG
        dlog(
            "workspace.gitProbe.schedule workspace=\(workspaceId.uuidString.prefix(5)) " +
            "panel=\(panelId.uuidString.prefix(5)) dir=\(normalizedDirectory) reason=\(reason)"
        )
#endif

        var timers: [DispatchSourceTimer] = []
        for (index, delay) in delays.enumerated() {
            let isLastAttempt = index == delays.count - 1
            let timer = DispatchSource.makeTimerSource(queue: initialWorkspaceGitProbeQueue)
            timer.schedule(deadline: .now() + delay, repeating: .never)
            timer.setEventHandler { [weak self] in
                let snapshot = Self.initialWorkspaceGitMetadataSnapshot(for: normalizedDirectory)
                Task { @MainActor [weak self] in
                    self?.applyWorkspaceGitMetadataSnapshot(
                        snapshot,
                        generation: generation,
                        probeKey: key,
                        expectedDirectory: normalizedDirectory,
                        isLastAttempt: isLastAttempt
                    )
                }
            }
            timers.append(timer)
            timer.resume()
        }
        workspaceGitProbeTimersByKey[key] = timers
    }

    private func cancelWorkspaceGitProbeTimers(for key: WorkspaceGitProbeKey) {
        guard let timers = workspaceGitProbeTimersByKey.removeValue(forKey: key) else {
            return
        }
        for timer in timers {
            timer.setEventHandler {}
            timer.cancel()
        }
    }

    private func clearWorkspaceGitProbe(_ key: WorkspaceGitProbeKey) {
        workspaceGitProbeGenerationByKey.removeValue(forKey: key)
        cancelWorkspaceGitProbeTimers(for: key)
    }

    private func clearWorkspaceGitProbes(workspaceId: UUID) {
        let keys = Set(workspaceGitProbeGenerationByKey.keys.filter { $0.workspaceId == workspaceId })
            .union(workspaceGitProbeTimersByKey.keys.filter { $0.workspaceId == workspaceId })
        for key in keys {
            clearWorkspaceGitProbe(key)
        }
    }

    private func applyWorkspaceGitMetadataSnapshot(
        _ snapshot: InitialWorkspaceGitMetadataSnapshot,
        generation: UUID,
        probeKey: WorkspaceGitProbeKey,
        expectedDirectory: String,
        isLastAttempt: Bool
    ) {
        defer {
            if shouldStopWorkspaceGitMetadataRefresh(snapshot) || isLastAttempt,
               workspaceGitProbeGenerationByKey[probeKey] == generation {
                clearWorkspaceGitProbe(probeKey)
            }
        }

        guard workspaceGitProbeGenerationByKey[probeKey] == generation else { return }
        guard let workspace = tabs.first(where: { $0.id == probeKey.workspaceId }) else {
            clearWorkspaceGitProbe(probeKey)
            return
        }
        guard workspace.panels[probeKey.panelId] != nil else {
            clearWorkspaceGitProbe(probeKey)
            return
        }

        guard let currentDirectory = gitProbeDirectory(for: workspace, panelId: probeKey.panelId) else {
            clearWorkspaceGitProbe(probeKey)
            return
        }
        if currentDirectory != expectedDirectory {
            clearWorkspaceGitProbe(probeKey)
#if DEBUG
            dlog(
                "workspace.gitProbe.skip workspace=\(probeKey.workspaceId.uuidString.prefix(5)) " +
                "panel=\(probeKey.panelId.uuidString.prefix(5)) reason=directoryChanged " +
                "expected=\(expectedDirectory) current=\(currentDirectory)"
            )
#endif
            return
        }

        workspace.updatePanelDirectory(panelId: probeKey.panelId, directory: expectedDirectory)

        let nextBranch = snapshot.branch
        if let nextBranch {
            workspace.updatePanelGitBranch(
                panelId: probeKey.panelId,
                branch: nextBranch,
                isDirty: snapshot.isDirty
            )
        } else {
            workspace.clearPanelGitBranch(panelId: probeKey.panelId)
        }

        switch snapshot.pullRequest {
        case .resolved(let pullRequest):
            workspace.updatePanelPullRequest(
                panelId: probeKey.panelId,
                number: pullRequest.number,
                label: pullRequest.label,
                url: pullRequest.url,
                status: pullRequest.status,
                checks: pullRequest.checks
            )
        case .notFound:
            if workspace.panelPullRequests[probeKey.panelId] != nil {
                workspace.clearPanelPullRequest(panelId: probeKey.panelId)
            }
        case .unsupportedRepository, .transientFailure:
            break
        }

#if DEBUG
        let branchLabel = snapshot.branch ?? "none"
        let prLabel: String = {
            switch snapshot.pullRequest {
            case .unsupportedRepository:
                return "unsupported"
            case .notFound:
                return "none"
            case .transientFailure:
                return "transientFailure"
            case .resolved(let pullRequest):
                let checks = pullRequest.checks?.rawValue ?? "none"
                return "#\(pullRequest.number):\(pullRequest.status.rawValue):\(checks)"
            }
        }()
        dlog(
            "workspace.gitProbe.apply workspace=\(probeKey.workspaceId.uuidString.prefix(5)) " +
            "panel=\(probeKey.panelId.uuidString.prefix(5)) branch=\(branchLabel) dirty=\(snapshot.isDirty ? 1 : 0) " +
            "pr=\(prLabel)"
        )
#endif
    }

    private func shouldStopWorkspaceGitMetadataRefresh(
        _ snapshot: InitialWorkspaceGitMetadataSnapshot
    ) -> Bool {
        switch snapshot.pullRequest {
        case .transientFailure:
            return false
        case .unsupportedRepository, .notFound, .resolved:
            return true
        }
    }

    private nonisolated static func initialWorkspaceGitMetadataSnapshot(
        for directory: String
    ) -> InitialWorkspaceGitMetadataSnapshot {
        let branch = normalizedBranchName(runGitCommand(directory: directory, arguments: ["branch", "--show-current"]))
        guard let branch else {
            return InitialWorkspaceGitMetadataSnapshot(
                branch: nil,
                isDirty: false,
                pullRequest: .notFound
            )
        }

        let statusOutput = runGitCommand(directory: directory, arguments: ["status", "--porcelain", "-uno"])
        let isDirty = !(statusOutput?.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty ?? true)
        let pullRequest = workspacePullRequestSnapshot(directory: directory, branch: branch)
        return InitialWorkspaceGitMetadataSnapshot(branch: branch, isDirty: isDirty, pullRequest: pullRequest)
    }

    private nonisolated static func runGitCommand(directory: String, arguments: [String]) -> String? {
        runCommand(
            directory: directory,
            executable: "git",
            arguments: arguments
        )
    }

    private nonisolated static func workspacePullRequestSnapshot(
        directory: String,
        branch: String
    ) -> WorkspacePullRequestSnapshot {
        guard !shouldSkipWorkspacePullRequestLookup(branch: branch) else {
            return .notFound
        }

        let repoSlugs = githubRepositorySlugs(directory: directory)
        guard !repoSlugs.isEmpty else {
            return .unsupportedRepository
        }

        var sawTransientFailure = false
        for repoSlug in repoSlugs {
            switch workspacePullRequestSnapshot(directory: directory, branch: branch, repoSlug: repoSlug) {
            case .resolved(let pullRequest):
                return .resolved(pullRequest)
            case .transientFailure:
                sawTransientFailure = true
            case .notFound, .unsupportedRepository:
                continue
            }
        }

        return sawTransientFailure ? .transientFailure : .notFound
    }

    private nonisolated static func workspacePullRequestSnapshot(
        directory: String,
        branch: String,
        repoSlug: String
    ) -> WorkspacePullRequestSnapshot {
        let result = runCommandResult(
            directory: directory,
            executable: "gh",
            arguments: [
                "pr", "list",
                "--repo", repoSlug,
                "--state", "all",
                "--head", branch,
                "--json", "number,state,url,updatedAt",
            ],
            timeout: workspacePullRequestProbeTimeout
        )

        guard let result else {
#if DEBUG
            dlog(
                "workspace.gitProbe.pr.fail dir=\(directory) branch=\(branch) " +
                "repo=\(repoSlug) status=nil"
            )
#endif
            return .transientFailure
        }

        guard !result.timedOut,
              result.executionError == nil,
              let exitStatus = result.exitStatus else {
#if DEBUG
            let statusText: String
            if result.timedOut {
                statusText = "timeout"
            } else if let executionError = result.executionError {
                statusText = "error=\(executionError)"
            } else {
                statusText = "unknown"
            }
            let stderr = debugLogSnippet(result.stderr) ?? "none"
            dlog(
                "workspace.gitProbe.pr.fail dir=\(directory) branch=\(branch) " +
                "repo=\(repoSlug) status=\(statusText) stderr=\(stderr)"
            )
#endif
            return .transientFailure
        }

        if exitStatus != 0 {
#if DEBUG
            dlog(
                "workspace.gitProbe.pr.fail dir=\(directory) branch=\(branch) " +
                "repo=\(repoSlug) status=exit=\(exitStatus) stderr=\(debugLogSnippet(result.stderr) ?? "none")"
            )
#endif
            return .transientFailure
        }

        let output = result.stdout ?? ""
        guard let pullRequests = decodeJSON([GitHubPullRequestProbeItem].self, from: output) else {
#if DEBUG
            dlog(
                "workspace.gitProbe.pr.parseFail dir=\(directory) branch=\(branch) " +
                "repo=\(repoSlug) output=\(debugLogSnippet(output) ?? "none")"
            )
#endif
            return .transientFailure
        }

        guard let pullRequest = preferredPullRequest(from: pullRequests) else {
#if DEBUG
            dlog(
                "workspace.gitProbe.pr.none dir=\(directory) branch=\(branch) " +
                "repo=\(repoSlug)"
            )
#endif
            return .notFound
        }

        guard let status = pullRequestStatus(from: pullRequest.state),
              let url = URL(string: pullRequest.url) else {
#if DEBUG
            dlog(
                "workspace.gitProbe.pr.parseFail dir=\(directory) branch=\(branch) " +
                "repo=\(repoSlug) output=\(debugLogSnippet(output) ?? "none")"
            )
#endif
            return .transientFailure
        }

        let checks = status == .open
            ? pullRequestChecksStatus(number: pullRequest.number, directory: directory, repoSlug: repoSlug)
            : nil

#if DEBUG
        dlog(
            "workspace.gitProbe.pr.success dir=\(directory) branch=\(branch) " +
            "repo=\(repoSlug) number=\(pullRequest.number) state=\(status.rawValue) checks=\(checks?.rawValue ?? "none")"
        )
#endif
        return .resolved(
            SidebarPullRequestState(
                number: pullRequest.number,
                label: "PR",
                url: url,
                status: status,
                branch: branch,
                checks: checks
            )
        )
    }

    nonisolated static func preferredPullRequest(
        from pullRequests: [GitHubPullRequestProbeItem]
    ) -> GitHubPullRequestProbeItem? {
        func statusPriority(_ status: SidebarPullRequestStatus) -> Int {
            switch status {
            case .open:
                return 3
            case .merged:
                return 2
            case .closed:
                return 1
            }
        }

        func isPreferred(
            candidate: GitHubPullRequestProbeItem,
            over current: GitHubPullRequestProbeItem
        ) -> Bool {
            guard let candidateStatus = pullRequestStatus(from: candidate.state),
                  let currentStatus = pullRequestStatus(from: current.state) else {
                return false
            }

            let candidatePriority = statusPriority(candidateStatus)
            let currentPriority = statusPriority(currentStatus)
            if candidatePriority != currentPriority {
                return candidatePriority > currentPriority
            }

            let candidateUpdatedAt = candidate.updatedAt ?? ""
            let currentUpdatedAt = current.updatedAt ?? ""
            if candidateUpdatedAt != currentUpdatedAt {
                return candidateUpdatedAt > currentUpdatedAt
            }

            return candidate.number > current.number
        }

        var best: GitHubPullRequestProbeItem?
        for pullRequest in pullRequests {
            guard pullRequestStatus(from: pullRequest.state) != nil,
                  URL(string: pullRequest.url) != nil else {
                continue
            }
            guard let currentBest = best else {
                best = pullRequest
                continue
            }
            if isPreferred(candidate: pullRequest, over: currentBest) {
                best = pullRequest
            }
        }
        return best
    }

    private nonisolated static func pullRequestChecksStatus(
        number: Int,
        directory: String,
        repoSlug: String
    ) -> SidebarPullRequestChecksStatus? {
        let result = runCommandResult(
            directory: directory,
            executable: "gh",
            arguments: [
                "pr", "checks", String(number),
                "--repo", repoSlug,
                "--json", "bucket,state"
            ],
            timeout: workspacePullRequestProbeTimeout
        )

        guard let result,
              !result.timedOut,
              result.executionError == nil,
              let output = result.stdout,
              let exitStatus = result.exitStatus,
              exitStatus == 0 || exitStatus == 8,
              let checks = decodeJSON([GitHubPullRequestCheckItem].self, from: output) else {
            return nil
        }

        var sawPending = false
        var sawPass = false

        for check in checks {
            let bucket = check.bucket?.trimmingCharacters(in: .whitespacesAndNewlines).lowercased()
            let state = check.state?.trimmingCharacters(in: .whitespacesAndNewlines).lowercased()

            if isFailingCheckState(bucket: bucket, state: state) {
                return .fail
            }
            if isPendingCheckState(bucket: bucket, state: state) {
                sawPending = true
                continue
            }
            if isPassingCheckState(bucket: bucket, state: state) {
                sawPass = true
            }
        }

        if sawPending {
            return .pending
        }
        if sawPass {
            return .pass
        }
        return nil
    }

    private nonisolated static func pullRequestStatus(
        from rawState: String
    ) -> SidebarPullRequestStatus? {
        switch rawState.trimmingCharacters(in: .whitespacesAndNewlines).uppercased() {
        case "OPEN":
            return .open
        case "MERGED":
            return .merged
        case "CLOSED":
            return .closed
        default:
            return nil
        }
    }

    private nonisolated static func decodeJSON<T: Decodable>(_ type: T.Type, from text: String) -> T? {
        guard let data = text.data(using: .utf8) else { return nil }
        return try? JSONDecoder().decode(T.self, from: data)
    }

    private nonisolated static func isFailingCheckState(bucket: String?, state: String?) -> Bool {
        switch bucket ?? state ?? "" {
        case "fail", "failure", "failed", "error", "timed_out", "timedout",
             "cancel", "cancelled", "canceled", "action_required", "startup_failure":
            return true
        default:
            return false
        }
    }

    private nonisolated static func isPendingCheckState(bucket: String?, state: String?) -> Bool {
        switch bucket ?? state ?? "" {
        case "pending", "queued", "in_progress", "requested", "waiting", "expected":
            return true
        default:
            return false
        }
    }

    private nonisolated static func isPassingCheckState(bucket: String?, state: String?) -> Bool {
        switch bucket ?? state ?? "" {
        case "pass", "success", "successful", "completed", "neutral", "skipping", "skipped":
            return true
        default:
            return false
        }
    }

    private nonisolated static let fallbackCommandSearchDirectories: [String] = [
        "/opt/homebrew/bin",
        "/usr/local/bin",
        "/opt/local/bin",
    ]

    nonisolated static func resolvedCommandPathForTesting(
        executable: String,
        environment: [String: String],
        fallbackDirectories: [String]
    ) -> String? {
        resolvedCommandPath(
            executable: executable,
            environment: environment,
            fallbackDirectories: fallbackDirectories
        )
    }

    private nonisolated static func resolvedCommandPath(
        executable: String,
        environment: [String: String] = ProcessInfo.processInfo.environment,
        fallbackDirectories: [String] = fallbackCommandSearchDirectories
    ) -> String? {
        guard !executable.isEmpty else { return nil }
        let fileManager = FileManager.default
        if executable.contains("/") {
            return fileManager.isExecutableFile(atPath: executable) ? executable : nil
        }

        var searchDirectories: [String] = []
        var seenDirectories: Set<String> = []

        func appendSearchPath(_ path: String?) {
            guard let path else { return }
            for rawComponent in path.split(separator: ":") {
                let component = String(rawComponent).trimmingCharacters(in: .whitespacesAndNewlines)
                guard !component.isEmpty,
                      seenDirectories.insert(component).inserted else {
                    continue
                }
                searchDirectories.append(component)
            }
        }

        appendSearchPath(environment["PATH"])
        appendSearchPath(getenv("PATH").map { String(cString: $0) })
        if let bundledBinPath = Bundle.main.resourceURL?.appendingPathComponent("bin").path {
            appendSearchPath(bundledBinPath)
        }
        fallbackDirectories.forEach { appendSearchPath($0) }
        appendSearchPath("/usr/bin:/bin:/usr/sbin:/sbin")

        for directory in searchDirectories {
            let candidate = URL(fileURLWithPath: directory, isDirectory: true)
                .appendingPathComponent(executable)
                .path
            if fileManager.isExecutableFile(atPath: candidate) {
                return candidate
            }
        }
        return nil
    }

    private nonisolated static func runCommand(
        directory: String,
        executable: String,
        arguments: [String],
        timeout: TimeInterval? = nil
    ) -> String? {
        let result = runCommandResult(
            directory: directory,
            executable: executable,
            arguments: arguments,
            timeout: timeout
        )
        guard let result,
              result.exitStatus == 0,
              !result.timedOut else {
            return nil
        }
        return result.stdout
    }

    private nonisolated static func runCommandResult(
        directory: String,
        executable: String,
        arguments: [String],
        timeout: TimeInterval? = nil
    ) -> CommandResult? {
        let process = Process()
        let stdout = Pipe()
        let stderr = Pipe()
        if let resolvedExecutable = resolvedCommandPath(executable: executable) {
            process.executableURL = URL(fileURLWithPath: resolvedExecutable)
            process.arguments = arguments
        } else {
            process.executableURL = URL(fileURLWithPath: "/usr/bin/env")
            process.arguments = [executable] + arguments
        }
        process.currentDirectoryURL = URL(fileURLWithPath: directory)
        process.standardOutput = stdout
        process.standardError = stderr

        let completion = DispatchSemaphore(value: 0)
        process.terminationHandler = { _ in
            completion.signal()
        }

        do {
            try process.run()
        } catch {
            return CommandResult(
                stdout: nil,
                stderr: nil,
                exitStatus: nil,
                timedOut: false,
                executionError: String(describing: error)
            )
        }

        if let timeout,
           completion.wait(timeout: .now() + timeout) == .timedOut {
            process.terminate()
            if completion.wait(timeout: .now() + 0.2) == .timedOut {
                kill(process.processIdentifier, SIGKILL)
                _ = completion.wait(timeout: .now() + 0.2)
            }
            return CommandResult(
                stdout: nil,
                stderr: nil,
                exitStatus: nil,
                timedOut: true,
                executionError: nil
            )
        } else if timeout == nil {
            completion.wait()
        }

        let stdoutData = stdout.fileHandleForReading.readDataToEndOfFile()
        let stderrData = stderr.fileHandleForReading.readDataToEndOfFile()
        return CommandResult(
            stdout: String(data: stdoutData, encoding: .utf8),
            stderr: String(data: stderrData, encoding: .utf8),
            exitStatus: process.terminationStatus,
            timedOut: false,
            executionError: nil
        )
    }

    nonisolated static func githubRepositorySlugs(fromGitRemoteVOutput output: String) -> [String] {
        var slugByRemoteName: [String: String] = [:]

        for line in output.split(whereSeparator: \.isNewline) {
            let parts = line.split(whereSeparator: \.isWhitespace)
            guard parts.count >= 3 else { continue }

            let remoteName = String(parts[0])
            let remoteURL = String(parts[1])
            let remoteKind = String(parts[2])
            guard remoteKind == "(fetch)",
                  let repoSlug = githubRepositorySlug(fromRemoteURL: remoteURL) else {
                continue
            }

            if slugByRemoteName[remoteName] == nil {
                slugByRemoteName[remoteName] = repoSlug
            }
        }

        let orderedRemoteNames = slugByRemoteName.keys.sorted { lhs, rhs in
            let lhsPriority = githubRemotePriority(lhs)
            let rhsPriority = githubRemotePriority(rhs)
            if lhsPriority != rhsPriority {
                return lhsPriority < rhsPriority
            }
            return lhs < rhs
        }

        var orderedSlugs: [String] = []
        var seen: Set<String> = []
        for remoteName in orderedRemoteNames {
            guard let repoSlug = slugByRemoteName[remoteName],
                  seen.insert(repoSlug).inserted else {
                continue
            }
            orderedSlugs.append(repoSlug)
        }
        return orderedSlugs
    }

    private nonisolated static func githubRepositorySlugs(directory: String) -> [String] {
        guard let output = runGitCommand(directory: directory, arguments: ["remote", "-v"]) else {
            return []
        }
        return githubRepositorySlugs(fromGitRemoteVOutput: output)
    }

    private nonisolated static func githubRemotePriority(_ remoteName: String) -> Int {
        switch remoteName.lowercased() {
        case "upstream":
            return 0
        case "origin":
            return 1
        default:
            return 2
        }
    }

    private nonisolated static func githubRepositorySlug(fromRemoteURL remoteURL: String) -> String? {
        let trimmed = remoteURL.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !trimmed.isEmpty else { return nil }

        let githubPrefixes = [
            "git@github.com:",
            "ssh://git@github.com/",
            "https://github.com/",
            "http://github.com/",
            "git://github.com/",
        ]
        for prefix in githubPrefixes where trimmed.hasPrefix(prefix) {
            let path = String(trimmed.dropFirst(prefix.count))
            return normalizedGitHubRepositorySlug(path)
        }

        guard let url = URL(string: trimmed),
              let host = url.host?.lowercased(),
              host == "github.com" else {
            return nil
        }

        return normalizedGitHubRepositorySlug(url.path)
    }

    private nonisolated static func normalizedGitHubRepositorySlug(_ rawPath: String) -> String? {
        let trimmedPath = rawPath.trimmingCharacters(in: CharacterSet(charactersIn: "/"))
        guard !trimmedPath.isEmpty else { return nil }
        let components = trimmedPath.split(separator: "/").map(String.init)
        guard components.count >= 2 else { return nil }
        let owner = components[0]
        var repo = components[1]
        if repo.hasSuffix(".git") {
            repo.removeLast(4)
        }
        guard !owner.isEmpty, !repo.isEmpty else { return nil }
        return "\(owner)/\(repo)"
    }

    private nonisolated static func debugLogSnippet(_ value: String?) -> String? {
        let trimmed = value?.trimmingCharacters(in: .whitespacesAndNewlines) ?? ""
        guard !trimmed.isEmpty else { return nil }
        return String(trimmed.prefix(180))
    }

    private nonisolated static func normalizedBranchName(_ branch: String?) -> String? {
        let trimmed = branch?.trimmingCharacters(in: .whitespacesAndNewlines) ?? ""
        return trimmed.isEmpty ? nil : trimmed
    }

    nonisolated static func shouldSkipWorkspacePullRequestLookup(branch: String) -> Bool {
        switch normalizedBranchName(branch) {
        case "main", "master":
            return true
        default:
            return false
        }
    }

    func requestBackgroundWorkspaceLoad(for workspaceId: UUID) {
        guard !pendingBackgroundWorkspaceLoadIds.contains(workspaceId) else { return }
        var updated = pendingBackgroundWorkspaceLoadIds
        updated.insert(workspaceId)
        pendingBackgroundWorkspaceLoadIds = updated
    }

    func completeBackgroundWorkspaceLoad(for workspaceId: UUID) {
        guard pendingBackgroundWorkspaceLoadIds.contains(workspaceId) else { return }
        var updated = pendingBackgroundWorkspaceLoadIds
        updated.remove(workspaceId)
        pendingBackgroundWorkspaceLoadIds = updated
    }

    func retainDebugWorkspaceLoads(for workspaceIds: Set<UUID>) {
        guard !workspaceIds.isEmpty else { return }
        var updated = debugPinnedWorkspaceLoadIds
        updated.formUnion(workspaceIds)
        guard updated != debugPinnedWorkspaceLoadIds else { return }
        debugPinnedWorkspaceLoadIds = updated
    }

    func releaseDebugWorkspaceLoads(for workspaceIds: Set<UUID>) {
        guard !workspaceIds.isEmpty else { return }
        var updated = debugPinnedWorkspaceLoadIds
        updated.subtract(workspaceIds)
        guard updated != debugPinnedWorkspaceLoadIds else { return }
        debugPinnedWorkspaceLoadIds = updated
    }

    func pruneBackgroundWorkspaceLoads(existingIds: Set<UUID>) {
        let pruned = pendingBackgroundWorkspaceLoadIds.intersection(existingIds)
        if pruned != pendingBackgroundWorkspaceLoadIds {
            pendingBackgroundWorkspaceLoadIds = pruned
        }
        let retained = debugPinnedWorkspaceLoadIds.intersection(existingIds)
        if retained != debugPinnedWorkspaceLoadIds {
            debugPinnedWorkspaceLoadIds = retained
        }
    }

    // Keep addTab as convenience alias
    @discardableResult
    func addTab(select: Bool = true, eagerLoadTerminal: Bool = false) -> Workspace {
        addWorkspace(select: select, eagerLoadTerminal: eagerLoadTerminal)
    }

    func terminalPanelForWorkspaceConfigInheritanceSource() -> TerminalPanel? {
        terminalPanelForWorkspaceConfigInheritanceSource(workspace: selectedWorkspace)
    }

    /// Build a snapshot using pre-extracted value-type data. The caller is responsible
    /// for obtaining `preferredWorkingDirectory` and `inheritedTerminalFontPoints` through
    /// `self` (where `self.tabs` keeps all Workspace objects alive) so that no local
    /// Workspace references are needed here.
    private func workspaceCreationSnapshotLite(
        currentTabs: [Workspace],
        currentSelectedTabId: UUID?,
        preferredWorkingDirectory: String?,
        inheritedTerminalFontPoints: Float?
    ) -> WorkspaceCreationSnapshot {
        var tabSnapshots: [WorkspaceCreationTabSnapshot] = []
        tabSnapshots.reserveCapacity(currentTabs.count)
        for workspace in currentTabs {
            // Keep each Workspace alive while copying the tiny value snapshot out of it.
            // The optimized arm64 Nightly build can otherwise over-release during
            // Collection.map, crashing here in swift_release / snapshot creation.
            let snapshot = withExtendedLifetime(workspace) {
                WorkspaceCreationTabSnapshot(workspace: workspace)
            }
            tabSnapshots.append(snapshot)
        }
        let selectedTabSnapshot = currentSelectedTabId.flatMap { selectedTabId in
            tabSnapshots.first(where: { $0.id == selectedTabId })
        }

        return WorkspaceCreationSnapshot(
            tabs: tabSnapshots,
            selectedTabId: currentSelectedTabId,
            selectedTabWasPinned: selectedTabSnapshot?.isPinned ?? false,
            preferredWorkingDirectory: preferredWorkingDirectory,
            inheritedTerminalFontPoints: inheritedTerminalFontPoints
        )
    }

    private func workspaceCreationSnapshot() -> WorkspaceCreationSnapshot {
        workspaceCreationSnapshotLite(
            currentTabs: tabs,
            currentSelectedTabId: selectedTabId,
            preferredWorkingDirectory: preferredWorkingDirectoryForNewTab(),
            inheritedTerminalFontPoints: inheritedTerminalFontPointsForNewWorkspace()
        )
    }

    private func orderedLiveWorkspaceCreationTabs(
        from snapshot: WorkspaceCreationSnapshot
    ) -> [WorkspaceCreationTabSnapshot]? {
        let currentTabs = tabs
        let snapshotTabsById = Dictionary(uniqueKeysWithValues: snapshot.tabs.map { ($0.id, $0) })
        var orderedTabs: [WorkspaceCreationTabSnapshot] = []
        orderedTabs.reserveCapacity(currentTabs.count)

        for workspace in currentTabs {
            guard let tabSnapshot = snapshotTabsById[workspace.id] else {
#if DEBUG
                dlog(
                    "workspace.create.reentrantSnapshotFallback " +
                    "snapshotCount=\(snapshot.tabs.count) liveCount=\(currentTabs.count)"
                )
#endif
                return nil
            }
            orderedTabs.append(tabSnapshot)
        }

        return orderedTabs
    }

    private func terminalPanelForWorkspaceConfigInheritanceSource(
        workspace: Workspace?
    ) -> TerminalPanel? {
        guard let workspace else { return nil }
        // Prefer cached/published panel state here instead of walking live Bonsplit focus
        // during Cmd+N; rapid workspace creation can observe transient pane/tab selection.
        let panels = workspace.panels
        var candidates: [TerminalPanel] = []
        var seen: Set<UUID> = []

        func appendCandidate(_ panel: TerminalPanel?) {
            guard let panel, seen.insert(panel.id).inserted else { return }
            candidates.append(panel)
        }

        appendCandidate(workspace.lastRememberedTerminalPanelForConfigInheritance())
        for terminalPanel in panels.values
            .compactMap({ $0 as? TerminalPanel })
            .sorted(by: { $0.id.uuidString < $1.id.uuidString }) {
            appendCandidate(terminalPanel)
        }

        if let livePanel = candidates.first(where: { $0.surface.hasLiveSurface && $0.surface.surface != nil }) {
            return livePanel
        }
        return candidates.first
    }

    private func inheritedTerminalConfigForNewWorkspace() -> CmuxSurfaceConfigTemplate? {
        inheritedTerminalConfigForNewWorkspace(workspace: selectedWorkspace)
    }

    private func cachedInheritedTerminalFontPointsForNewWorkspace(
        workspace: Workspace?
    ) -> Float? {
        guard let workspace else { return nil }
        // New workspace creation only seeds font size into a fresh Swift-owned template.
        // Avoid reading live panel/surface state here; the arm64 Nightly Cmd+N crash path
        // was repeatedly dereferencing pointer-backed terminal objects while preparing the
        // new workspace. The workspace already caches the rooted font lineage we need.
        return withExtendedLifetime(workspace) {
            guard let fontPoints = workspace.lastRememberedTerminalFontPointsForConfigInheritance(),
                  fontPoints > 0 else {
                return nil
            }
            return fontPoints
        }
    }

    func inheritedTerminalConfigForNewWorkspace(
        workspace: Workspace?
    ) -> CmuxSurfaceConfigTemplate? {
        guard let fontPoints = cachedInheritedTerminalFontPointsForNewWorkspace(workspace: workspace) else {
            return nil
        }
        var config = CmuxSurfaceConfigTemplate()
        config.fontSize = fontPoints
        return config
    }

    private func inheritedTerminalFontPointsForNewWorkspace() -> Float? {
        inheritedTerminalFontPointsForNewWorkspace(workspace: selectedWorkspace)
    }

    private func inheritedTerminalFontPointsForNewWorkspace(
        workspace: Workspace?
    ) -> Float? {
        cachedInheritedTerminalFontPointsForNewWorkspace(workspace: workspace)
    }

    private func workspaceCreationConfigTemplate(
        inheritedTerminalFontPoints: Float?
    ) -> CmuxSurfaceConfigTemplate? {
        guard let inheritedTerminalFontPoints, inheritedTerminalFontPoints > 0 else {
            return nil
        }
        // Rebuild a clean Swift-owned template instead of carrying over any pointer-backed
        // inherited config state from the source workspace.
        var config = CmuxSurfaceConfigTemplate()
        config.fontSize = inheritedTerminalFontPoints
        return config
    }

    private func normalizedWorkingDirectory(_ directory: String?) -> String? {
        guard let directory else { return nil }
        let normalized = normalizeDirectory(directory)
        let trimmed = normalized.trimmingCharacters(in: .whitespacesAndNewlines)
        return trimmed.isEmpty ? nil : normalized
    }

    private func newTabInsertIndex(placementOverride: NewWorkspacePlacement? = nil) -> Int {
        newTabInsertIndex(snapshot: workspaceCreationSnapshot(), placementOverride: placementOverride)
    }

    private func newTabInsertIndex(
        snapshot: WorkspaceCreationSnapshot,
        placementOverride: NewWorkspacePlacement? = nil
    ) -> Int {
        let placement = placementOverride ?? WorkspacePlacementSettings.current()
        let liveTabs = orderedLiveWorkspaceCreationTabs(from: snapshot) ?? snapshot.tabs
        let pinnedCount = liveTabs.reduce(into: 0) { partial, tab in
            if tab.isPinned {
                partial += 1
            }
        }

        switch placement {
        case .top:
            return pinnedCount
        case .end:
            return liveTabs.count
        case .afterCurrent:
            if let selectedTabId = snapshot.selectedTabId,
               let selectedIndex = liveTabs.firstIndex(where: { $0.id == selectedTabId }) {
                return WorkspacePlacementSettings.insertionIndex(
                    placement: placement,
                    selectedIndex: selectedIndex,
                    selectedIsPinned: snapshot.selectedTabWasPinned,
                    pinnedCount: pinnedCount,
                    totalCount: liveTabs.count
                )
            }
            return snapshot.selectedTabWasPinned ? pinnedCount : liveTabs.count
        }
    }

    private func preferredWorkingDirectoryForNewTab() -> String? {
        preferredWorkingDirectoryForNewTab(workspace: selectedWorkspace)
    }

    private func preferredWorkingDirectoryForNewTab(
        workspace: Workspace?
    ) -> String? {
        guard let workspace else {
            return nil
        }
        // Use cached directory state only; avoiding live focus traversal keeps workspace
        // creation resilient when Bonsplit is in the middle of a rapid Cmd+N churn.
        if let currentDirectory = normalizedWorkingDirectory(workspace.currentDirectory) {
            return currentDirectory
        }

        return workspace.panelDirectories.values.lazy.compactMap { directory in
            self.normalizedWorkingDirectory(directory)
        }.first
    }

    func moveTabToTop(_ tabId: UUID) {
        guard let index = tabs.firstIndex(where: { $0.id == tabId }) else { return }
        guard index != 0 else { return }
        let tab = tabs.remove(at: index)
        let pinnedCount = tabs.filter { $0.isPinned }.count
        let insertIndex = tab.isPinned ? 0 : pinnedCount
        tabs.insert(tab, at: insertIndex)
    }

    func moveTabsToTop(_ tabIds: Set<UUID>) {
        guard !tabIds.isEmpty else { return }
        let selectedTabs = tabs.filter { tabIds.contains($0.id) }
        guard !selectedTabs.isEmpty else { return }
        let remainingTabs = tabs.filter { !tabIds.contains($0.id) }
        let selectedPinned = selectedTabs.filter { $0.isPinned }
        let selectedUnpinned = selectedTabs.filter { !$0.isPinned }
        let remainingPinned = remainingTabs.filter { $0.isPinned }
        let remainingUnpinned = remainingTabs.filter { !$0.isPinned }
        tabs = selectedPinned + remainingPinned + selectedUnpinned + remainingUnpinned
    }

    func moveTabToTopForNotification(_ tabId: UUID) {
        guard let index = tabs.firstIndex(where: { $0.id == tabId }) else { return }
        let pinnedCount = tabs.filter { $0.isPinned }.count
        guard index != pinnedCount else { return }
        let tab = tabs[index]
        guard !tab.isPinned else { return }
        tabs.remove(at: index)
        tabs.insert(tab, at: pinnedCount)
    }

    @discardableResult
    func reorderWorkspace(tabId: UUID, toIndex targetIndex: Int) -> Bool {
        guard let currentIndex = tabs.firstIndex(where: { $0.id == tabId }) else { return false }
        if tabs.count <= 1 { return true }

        let workspace = tabs[currentIndex]
        let clamped = clampedReorderIndex(for: workspace, targetIndex: targetIndex)
        if currentIndex == clamped { return true }

        tabs.remove(at: currentIndex)
        tabs.insert(workspace, at: clamped)
        return true
    }

    @discardableResult
    func reorderWorkspace(tabId: UUID, before beforeId: UUID? = nil, after afterId: UUID? = nil) -> Bool {
        guard tabs.contains(where: { $0.id == tabId }) else { return false }
        if let beforeId {
            guard let idx = tabs.firstIndex(where: { $0.id == beforeId }) else { return false }
            return reorderWorkspace(tabId: tabId, toIndex: idx)
        }
        if let afterId {
            guard let idx = tabs.firstIndex(where: { $0.id == afterId }) else { return false }
            return reorderWorkspace(tabId: tabId, toIndex: idx + 1)
        }
        return false
    }

    func setCustomTitle(tabId: UUID, title: String?) {
        guard let index = tabs.firstIndex(where: { $0.id == tabId }) else { return }
        tabs[index].setCustomTitle(title)
        if selectedTabId == tabId {
            updateWindowTitle(for: tabs[index])
        }
    }

    func clearCustomTitle(tabId: UUID) {
        setCustomTitle(tabId: tabId, title: nil)
    }

    func setTabColor(tabId: UUID, color: String?) {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return }
        tab.setCustomColor(color)
    }

    func togglePin(tabId: UUID) {
        guard let index = tabs.firstIndex(where: { $0.id == tabId }) else { return }
        let tab = tabs[index]
        setPinned(tab, pinned: !tab.isPinned)
    }

    func setPinned(_ tab: Workspace, pinned: Bool) {
        guard tab.isPinned != pinned else { return }
        tab.isPinned = pinned
        reorderTabForPinnedState(tab)
    }

    private func reorderTabForPinnedState(_ tab: Workspace) {
        guard let index = tabs.firstIndex(where: { $0.id == tab.id }) else { return }
        tabs.remove(at: index)
        let pinnedCount = tabs.filter { $0.isPinned }.count
        let insertIndex = min(pinnedCount, tabs.count)
        tabs.insert(tab, at: insertIndex)
    }

    private func clampedReorderIndex(for workspace: Workspace, targetIndex: Int) -> Int {
        let clamped = max(0, min(targetIndex, tabs.count - 1))
        let pinnedCount = tabs.filter { $0.isPinned }.count
        if workspace.isPinned {
            return min(clamped, max(0, pinnedCount - 1))
        }
        return max(clamped, pinnedCount)
    }

    // MARK: - Surface Directory Updates (Backwards Compatibility)

    func updateSurfaceDirectory(tabId: UUID, surfaceId: UUID, directory: String) {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return }
        let previousDirectory = gitProbeDirectory(for: tab, panelId: surfaceId)
        let normalized = normalizeDirectory(directory)
        tab.updatePanelDirectory(panelId: surfaceId, directory: normalized)
        let nextDirectory = normalizedWorkingDirectory(normalized)
        if previousDirectory != nextDirectory {
            scheduleWorkspaceGitMetadataRefreshIfPossible(
                workspaceId: tabId,
                panelId: surfaceId,
                reason: "directoryChange"
            )
        }
    }

    func updateSurfaceGitBranch(
        tabId: UUID,
        surfaceId: UUID,
        branch: String,
        isDirty: Bool
    ) {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return }
        let current = tab.panelGitBranches[surfaceId]
        let normalizedBranch = Self.normalizedBranchName(branch) ?? branch
        guard current?.branch != normalizedBranch || current?.isDirty != isDirty else { return }
        tab.updatePanelGitBranch(panelId: surfaceId, branch: normalizedBranch, isDirty: isDirty)
        scheduleWorkspaceGitMetadataRefreshIfPossible(
            workspaceId: tabId,
            panelId: surfaceId,
            reason: "branchChange"
        )
    }

    func clearSurfaceGitBranch(tabId: UUID, surfaceId: UUID) {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return }
        let hadBranch = tab.panelGitBranches[surfaceId] != nil
        let hadPullRequest = tab.panelPullRequests[surfaceId] != nil
        guard hadBranch || hadPullRequest else { return }
        tab.clearPanelGitBranch(panelId: surfaceId)
        tab.clearPanelPullRequest(panelId: surfaceId)
        scheduleWorkspaceGitMetadataRefreshIfPossible(
            workspaceId: tabId,
            panelId: surfaceId,
            reason: "branchCleared"
        )
    }

    func updateSurfaceShellActivity(
        tabId: UUID,
        surfaceId: UUID,
        state: Workspace.PanelShellActivityState
    ) {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return }
        tab.updatePanelShellActivityState(panelId: surfaceId, state: state)
    }

    func updateSurfaceTmuxState(
        tabId: UUID,
        surfaceId: UUID,
        isInsideTmux: Bool
    ) {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return }
        tab.updatePanelTmuxState(panelId: surfaceId, isInsideTmux: isInsideTmux)
    }

    private func normalizeDirectory(_ directory: String) -> String {
        let trimmed = directory.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !trimmed.isEmpty else { return directory }
        if trimmed.hasPrefix("file://"), let url = URL(string: trimmed) {
            if !url.path.isEmpty {
                return url.path
            }
        }
        return trimmed
    }

    func closeWorkspace(_ workspace: Workspace) {
        guard tabs.count > 1 else { return }
        sentryBreadcrumb("workspace.close", data: ["tabCount": tabs.count - 1])
        clearWorkspaceGitProbes(workspaceId: workspace.id)
        sidebarSelectedWorkspaceIds.remove(workspace.id)

        AppDelegate.shared?.notificationStore?.clearNotifications(forTabId: workspace.id)
        workspace.teardownAllPanels()
        workspace.teardownRemoteConnection()
        unwireClosedBrowserTracking(for: workspace)
        workspace.owningTabManager = nil

        if let index = tabs.firstIndex(where: { $0.id == workspace.id }) {
            tabs.remove(at: index)

            if selectedTabId == workspace.id {
                // Keep the "focused index" stable when possible:
                // - If we closed workspace i and there is still a workspace at index i, focus it (the one that moved up).
                // - Otherwise (we closed the last workspace), focus the new last workspace (i-1).
                let newIndex = min(index, max(0, tabs.count - 1))
                selectedTabId = tabs[newIndex].id
            }
        }
    }

    /// Detach a workspace from this window without closing its panels.
    /// Used by the socket API for cross-window moves.
    @discardableResult
    func detachWorkspace(tabId: UUID) -> Workspace? {
        guard let index = tabs.firstIndex(where: { $0.id == tabId }) else { return nil }
        clearWorkspaceGitProbes(workspaceId: tabId)
        sidebarSelectedWorkspaceIds.remove(tabId)

        let removed = tabs.remove(at: index)
        unwireClosedBrowserTracking(for: removed)
        removed.owningTabManager = nil
        lastFocusedPanelByTab.removeValue(forKey: removed.id)

        if tabs.isEmpty {
            // The UI assumes each window always has at least one workspace.
            _ = addWorkspace()
            return removed
        }

        if selectedTabId == removed.id {
            let nextIndex = min(index, max(0, tabs.count - 1))
            selectedTabId = tabs[nextIndex].id
        }

        return removed
    }

    /// Attach an existing workspace to this window.
    func attachWorkspace(_ workspace: Workspace, at index: Int? = nil, select: Bool = true) {
        workspace.owningTabManager = self
        wireClosedBrowserTracking(for: workspace)
        let insertIndex: Int = {
            guard let index else { return tabs.count }
            return max(0, min(index, tabs.count))
        }()
        tabs.insert(workspace, at: insertIndex)
        if select {
            selectedTabId = workspace.id
        }
    }

    // Keep closeTab as convenience alias
    func closeTab(_ tab: Workspace) { closeWorkspace(tab) }
    func closeCurrentTabWithConfirmation() { closeCurrentWorkspaceWithConfirmation() }

    func closeCurrentWorkspace() {
        guard let selectedId = selectedTabId,
              let workspace = tabs.first(where: { $0.id == selectedId }) else { return }
        closeWorkspace(workspace)
    }

    func closeCurrentPanelWithConfirmation() {
#if DEBUG
        UITestRecorder.incrementInt("closePanelInvocations")
#endif
        guard let selectedId = selectedTabId,
              let tab = tabs.first(where: { $0.id == selectedId }),
              let focusedPanelId = tab.focusedPanelId else { return }
        closePanelWithConfirmation(tab: tab, panelId: focusedPanelId)
    }

    func canCloseOtherTabsInFocusedPane() -> Bool {
        closeOtherTabsInFocusedPanePlan() != nil
    }

    func closeOtherTabsInFocusedPaneWithConfirmation() {
        guard let plan = closeOtherTabsInFocusedPanePlan() else { return }

        let count = plan.panelIds.count
        let titleLines = plan.titles.map { "• \($0)" }.joined(separator: "\n")
        let message = "This is about to close \(count) tab\(count == 1 ? "" : "s") in this pane:\n\(titleLines)"
        guard confirmClose(
            title: "Close other tabs?",
            message: message,
            acceptCmdD: false
        ) else { return }

        for panelId in plan.panelIds {
            _ = plan.workspace.closePanel(panelId, force: true)
        }
    }

    func closeCurrentWorkspaceWithConfirmation() {
#if DEBUG
        UITestRecorder.incrementInt("closeTabInvocations")
#endif
        let sidebarSelectionIds = orderedSidebarSelectedWorkspaceIds()
        if sidebarSelectionIds.count > 1 {
            closeWorkspacesWithConfirmation(sidebarSelectionIds, allowPinned: true)
            return
        }
        guard let selectedId = selectedTabId,
              let workspace = tabs.first(where: { $0.id == selectedId }) else { return }
        closeWorkspaceWithConfirmation(workspace)
    }

    func canCloseWorkspace(_ workspace: Workspace, allowPinned: Bool = false) -> Bool {
        allowPinned || !workspace.isPinned
    }

    @discardableResult
    func closeWorkspaceWithConfirmation(_ workspace: Workspace) -> Bool {
        if workspace.isPinned {
            guard confirmClose(
                title: String(localized: "dialog.closePinnedWorkspace.title", defaultValue: "Close pinned workspace?"),
                message: String(
                    localized: "dialog.closePinnedWorkspace.message",
                    defaultValue: "This workspace is pinned. Closing it will close the workspace and all of its panels."
                ),
                acceptCmdD: tabs.count <= 1
            ) else {
                return false
            }
            closeWorkspaceIfRunningProcess(workspace, requiresConfirmation: false)
            return true
        }
        closeWorkspaceIfRunningProcess(workspace)
        return true
    }

    @discardableResult
    func closeWorkspaceWithConfirmation(tabId: UUID) -> Bool {
        guard let workspace = tabs.first(where: { $0.id == tabId }) else { return false }
        return closeWorkspaceWithConfirmation(workspace)
    }

    func setSidebarSelectedWorkspaceIds(_ workspaceIds: Set<UUID>) {
        let existingIds = Set(tabs.map(\.id))
        sidebarSelectedWorkspaceIds = workspaceIds.intersection(existingIds)
    }

    func closeWorkspacesWithConfirmation(_ workspaceIds: [UUID], allowPinned: Bool) {
        let workspaces = orderedClosableWorkspaces(workspaceIds, allowPinned: allowPinned)
        guard !workspaces.isEmpty else { return }
        guard workspaces.count > 1 else {
            closeWorkspaceWithConfirmation(workspaces[0])
            return
        }

        let plan = closeWorkspacesPlan(for: workspaces)
        guard confirmClose(
            title: plan.title,
            message: plan.message,
            acceptCmdD: plan.acceptCmdD
        ) else { return }

        for workspace in plan.workspaces {
            guard tabs.contains(where: { $0.id == workspace.id }) else { continue }
            closeWorkspaceIfRunningProcess(workspace, requiresConfirmation: false)
        }
    }

    func selectWorkspace(_ workspace: Workspace) {
#if DEBUG
        debugPrimeWorkspaceSwitchTrigger("select", to: workspace.id)
#endif
        selectedTabId = workspace.id
    }

    // Keep selectTab as convenience alias
    func selectTab(_ tab: Workspace) { selectWorkspace(tab) }

    private func confirmClose(title: String, message: String, acceptCmdD: Bool) -> Bool {
        if let confirmCloseHandler {
            return confirmCloseHandler(title, message, acceptCmdD)
        }
        _ = acceptCmdD

        let alert = NSAlert()
        alert.messageText = title
        alert.informativeText = message
        alert.alertStyle = .warning
        alert.addButton(withTitle: String(localized: "dialog.closeTab.close", defaultValue: "Close"))
        alert.addButton(withTitle: String(localized: "dialog.closeTab.cancel", defaultValue: "Cancel"))

        if let closeButton = alert.buttons.first {
            closeButton.keyEquivalent = "\r"
            closeButton.keyEquivalentModifierMask = []
            alert.window.defaultButtonCell = closeButton.cell as? NSButtonCell
            alert.window.initialFirstResponder = closeButton
        }
        if let cancelButton = alert.buttons.dropFirst().first {
            cancelButton.keyEquivalent = "\u{1b}"
        }

        if NSApp.activationPolicy() == .regular {
            NSApp.activate(ignoringOtherApps: true)
        }

        return alert.runModal() == .alertFirstButtonReturn
    }

    private struct CloseOtherTabsInFocusedPanePlan {
        let workspace: Workspace
        let panelIds: [UUID]
        let titles: [String]
    }

    private struct CloseWorkspacesPlan {
        let workspaces: [Workspace]
        let title: String
        let message: String
        let acceptCmdD: Bool
    }

    private func closeOtherTabsInFocusedPanePlan() -> CloseOtherTabsInFocusedPanePlan? {
        guard let workspace = selectedWorkspace else { return nil }
        guard let paneId = workspace.bonsplitController.focusedPaneId ?? workspace.bonsplitController.allPaneIds.first else {
            return nil
        }

        let tabsInPane = workspace.bonsplitController.tabs(inPane: paneId)
        guard !tabsInPane.isEmpty else { return nil }
        guard let selectedTabId = workspace.bonsplitController.selectedTab(inPane: paneId)?.id ?? tabsInPane.first?.id else {
            return nil
        }

        var targetPanelIds: [UUID] = []
        var targetTitles: [String] = []
        for tab in tabsInPane where tab.id != selectedTabId {
            guard let panelId = workspace.panelIdFromSurfaceId(tab.id) else { continue }
            if workspace.isPanelPinned(panelId) {
                continue
            }
            targetPanelIds.append(panelId)
            targetTitles.append(closeOtherTabsDisplayTitle(workspace.panelTitle(panelId: panelId)))
        }

        guard !targetPanelIds.isEmpty else { return nil }
        return CloseOtherTabsInFocusedPanePlan(
            workspace: workspace,
            panelIds: targetPanelIds,
            titles: targetTitles
        )
    }

    private func closeOtherTabsDisplayTitle(_ title: String?) -> String {
        let collapsed = title?
            .replacingOccurrences(of: "\n", with: " ")
            .replacingOccurrences(of: "\r", with: " ")
            .trimmingCharacters(in: .whitespacesAndNewlines)
        if let collapsed, !collapsed.isEmpty {
            return collapsed
        }
        return "Untitled Tab"
    }

    private func orderedClosableWorkspaces(_ workspaceIds: [UUID], allowPinned: Bool) -> [Workspace] {
        let targetIds = Set(workspaceIds)
        return tabs.compactMap { workspace in
            guard targetIds.contains(workspace.id) else { return nil }
            guard allowPinned || !workspace.isPinned else { return nil }
            return workspace
        }
    }

    private func orderedSidebarSelectedWorkspaceIds() -> [UUID] {
        tabs.compactMap { workspace in
            sidebarSelectedWorkspaceIds.contains(workspace.id) ? workspace.id : nil
        }
    }

    private func closeWorkspacesPlan(for workspaces: [Workspace]) -> CloseWorkspacesPlan {
        let willCloseWindow = workspaces.count == tabs.count
        let title = willCloseWindow
            ? String(localized: "dialog.closeWindow.title", defaultValue: "Close window?")
            : String(localized: "dialog.closeWorkspaces.title", defaultValue: "Close workspaces?")
        let titleLines = workspaces
            .map { "• \(closeWorkspaceDisplayTitle($0.title))" }
            .joined(separator: "\n")
        let format = willCloseWindow
            ? String(
                localized: "dialog.closeWorkspacesWindow.message",
                defaultValue: "This will close the current window, its %1$lld workspaces, and all of their panels:\n%2$@"
            )
            : String(
                localized: "dialog.closeWorkspaces.message",
                defaultValue: "This will close %1$lld workspaces and all of their panels:\n%2$@"
            )
        let message = String(format: format, locale: .current, Int64(workspaces.count), titleLines)
        return CloseWorkspacesPlan(
            workspaces: workspaces,
            title: title,
            message: message,
            acceptCmdD: willCloseWindow
        )
    }

    private func closeWorkspaceDisplayTitle(_ title: String?) -> String {
        let collapsed = title?
            .replacingOccurrences(of: "\n", with: " ")
            .replacingOccurrences(of: "\r", with: " ")
            .trimmingCharacters(in: .whitespacesAndNewlines)
        if let collapsed, !collapsed.isEmpty {
            return collapsed
        }
        return String(localized: "workspace.displayName.fallback", defaultValue: "Workspace")
    }

    private func closeWorkspaceIfRunningProcess(_ workspace: Workspace, requiresConfirmation: Bool = true) {
        let willCloseWindow = tabs.count <= 1
        if requiresConfirmation,
           workspaceNeedsConfirmClose(workspace),
           !confirmClose(
               title: String(localized: "dialog.closeWorkspace.title", defaultValue: "Close workspace?"),
               message: String(localized: "dialog.closeWorkspace.message", defaultValue: "This will close the workspace and all of its panels."),
               acceptCmdD: willCloseWindow
           ) {
            return
        }
        if tabs.count <= 1 {
            // Last workspace in this window: close the window (Cmd+Shift+W behavior).
            if let window {
                window.performClose(nil)
            } else {
                AppDelegate.shared?.closeMainWindowContainingTabId(workspace.id)
            }
        } else {
            closeWorkspace(workspace)
        }
    }

    private func shouldCloseWorkspaceOnLastSurfaceShortcut(_ workspace: Workspace, panelId: UUID) -> Bool {
        LastSurfaceCloseShortcutSettings.closesWorkspace() &&
            workspace.panels.count <= 1 &&
            workspace.panels[panelId] != nil
    }

    private func closePanelWithConfirmation(tab: Workspace, panelId: UUID) {
        guard tab.panels[panelId] != nil else {
#if DEBUG
            dlog(
                "surface.close.shortcut.skip tab=\(tab.id.uuidString.prefix(5)) " +
                "panel=\(panelId.uuidString.prefix(5)) reason=missingPanel"
            )
#endif
            return
        }

        let bonsplitTabCount = tab.bonsplitController.allPaneIds.reduce(0) { partial, paneId in
            partial + tab.bonsplitController.tabs(inPane: paneId).count
        }
        let panelKind: String = {
            guard let panel = tab.panels[panelId] else { return "missing" }
            if panel is TerminalPanel { return "terminal" }
            if panel is BrowserPanel { return "browser" }
            return String(describing: type(of: panel))
        }()
        let closesWorkspaceOnLastSurfaceShortcut = shouldCloseWorkspaceOnLastSurfaceShortcut(tab, panelId: panelId)
#if DEBUG
        dlog(
            "surface.close.shortcut.begin tab=\(tab.id.uuidString.prefix(5)) " +
            "panel=\(panelId.uuidString.prefix(5)) kind=\(panelKind) " +
            "panelCount=\(tab.panels.count) bonsplitTabs=\(bonsplitTabCount) " +
            "closeWorkspaceOnLastSurface=\(closesWorkspaceOnLastSurfaceShortcut ? 1 : 0)"
        )
#endif

        // The last-surface shortcut preference only affects Cmd+W. The tab close button
        // continues to use Workspace's explicit-close path when it closes the last surface.
        if closesWorkspaceOnLastSurfaceShortcut,
           let surfaceId = tab.surfaceIdFromPanelId(panelId) {
            tab.markExplicitClose(surfaceId: surfaceId)
        }
        let closed = tab.closePanel(panelId)
#if DEBUG
        dlog(
            "surface.close.shortcut tab=\(tab.id.uuidString.prefix(5)) " +
            "panel=\(panelId.uuidString.prefix(5)) closed=\(closed ? 1 : 0) " +
            "panelsAfterCall=\(tab.panels.count)"
        )
#endif
    }

    func closePanelWithConfirmation(tabId: UUID, surfaceId: UUID) {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return }
        closePanelWithConfirmation(tab: tab, panelId: surfaceId)
    }

    /// Runtime close requests from Ghostty should only ever target the specific surface.
    /// They must not escalate into workspace/window-close semantics for "last tab".
    func closeRuntimeSurfaceWithConfirmation(tabId: UUID, surfaceId: UUID) {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return }
        guard tab.panels[surfaceId] != nil else { return }

        if let terminalPanel = tab.terminalPanel(for: surfaceId),
           tab.panelNeedsConfirmClose(panelId: surfaceId, fallbackNeedsConfirmClose: terminalPanel.needsConfirmClose()) {
            guard confirmClose(
                title: String(localized: "dialog.closeTab.title", defaultValue: "Close tab?"),
                message: String(localized: "dialog.closeTab.message", defaultValue: "This will close the current tab."),
                acceptCmdD: false
            ) else { return }
        }

        _ = tab.closePanel(surfaceId, force: true)
        AppDelegate.shared?.notificationStore?.clearNotifications(forTabId: tab.id, surfaceId: surfaceId)
    }

    /// Runtime close requests from Ghostty without confirmation (e.g. child-exit).
    /// This path must only close the addressed surface and must never close the workspace window.
    func closeRuntimeSurface(tabId: UUID, surfaceId: UUID) {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return }
        guard tab.panels[surfaceId] != nil else { return }

#if DEBUG
        dlog(
            "surface.close.runtime tab=\(tabId.uuidString.prefix(5)) " +
            "surface=\(surfaceId.uuidString.prefix(5)) panelsBefore=\(tab.panels.count)"
        )
#endif

        // Keep AppKit first responder in sync with workspace focus before routing the close.
        // If split reparenting caused a temporary model/view mismatch, fallback close logic in
        // Workspace.closePanel uses focused selection to resolve the correct tab deterministically.
        reconcileFocusedPanelFromFirstResponderForKeyboard()
        let closed = tab.closePanel(surfaceId, force: true)
#if DEBUG
        dlog(
            "surface.close.runtime.done tab=\(tabId.uuidString.prefix(5)) " +
            "surface=\(surfaceId.uuidString.prefix(5)) closed=\(closed ? 1 : 0) panelsAfter=\(tab.panels.count)"
        )
#endif
        AppDelegate.shared?.notificationStore?.clearNotifications(forTabId: tab.id, surfaceId: surfaceId)
    }

    /// Close a panel because its child process exited (e.g. the user hit Ctrl+D).
    ///
    /// This should never prompt: the process is already gone, and Ghostty emits the
    /// `SHOW_CHILD_EXITED` action specifically so the host app can decide what to do.
    func closePanelAfterChildExited(tabId: UUID, surfaceId: UUID) {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return }
        guard tab.panels[surfaceId] != nil else { return }
        let keepsRemoteWorkspaceOpen =
            tab.panels.count <= 1 && tab.shouldDemoteWorkspaceAfterChildExit(surfaceId: surfaceId)

#if DEBUG
        dlog(
            "surface.close.childExited tab=\(tabId.uuidString.prefix(5)) " +
            "surface=\(surfaceId.uuidString.prefix(5)) panels=\(tab.panels.count) workspaces=\(tabs.count) " +
            "remoteWorkspace=\(tab.isRemoteWorkspace ? 1 : 0) keepRemote=\(keepsRemoteWorkspaceOpen ? 1 : 0)"
        )
#endif

        // Exiting the last SSH surface should demote the workspace back to a local one.
        // Route through Workspace close handling so remote teardown and replacement-panel
        // logic run before TabManager considers removing the workspace itself, including
        // session-end paths where remote configuration was cleared before Ghostty delivered
        // the child-exit callback.
        if keepsRemoteWorkspaceOpen {
            closeRuntimeSurface(tabId: tabId, surfaceId: surfaceId)
            return
        }

        // Child-exit on the last panel should collapse the workspace, matching explicit close
        // semantics (and close the window when it was the last workspace).
        if tab.panels.count <= 1 {
            if tabs.count <= 1 {
                if let app = AppDelegate.shared {
                    app.notificationStore?.clearNotifications(forTabId: tabId)
                    app.closeMainWindowContainingTabId(tabId)
                } else {
                    // Headless/test fallback when no AppDelegate window context exists.
                    closeRuntimeSurface(tabId: tabId, surfaceId: surfaceId)
                }
            } else {
                closeWorkspace(tab)
            }
            return
        }

        closeRuntimeSurface(tabId: tabId, surfaceId: surfaceId)
    }

    private func workspaceNeedsConfirmClose(_ workspace: Workspace) -> Bool {
#if DEBUG
        if ProcessInfo.processInfo.environment["CMUX_UI_TEST_FORCE_CONFIRM_CLOSE_WORKSPACE"] == "1" {
            return true
        }
#endif
        return workspace.needsConfirmClose()
    }

    func titleForTab(_ tabId: UUID) -> String? {
        tabs.first(where: { $0.id == tabId })?.title
    }

    // MARK: - Panel/Surface ID Access

    /// Returns the focused panel ID for a tab (replaces focusedSurfaceId)
    func focusedPanelId(for tabId: UUID) -> UUID? {
        tabs.first(where: { $0.id == tabId })?.focusedPanelId
    }

    /// Returns the focused panel if it's a BrowserPanel, nil otherwise
    var focusedBrowserPanel: BrowserPanel? {
        guard let tab = selectedWorkspace,
              let panelId = tab.focusedPanelId else { return nil }
        return tab.panels[panelId] as? BrowserPanel
    }

    @discardableResult
    func zoomInFocusedBrowser() -> Bool {
        focusedBrowserPanel?.zoomIn() ?? false
    }

    @discardableResult
    func zoomOutFocusedBrowser() -> Bool {
        focusedBrowserPanel?.zoomOut() ?? false
    }

    @discardableResult
    func resetZoomFocusedBrowser() -> Bool {
        focusedBrowserPanel?.resetZoom() ?? false
    }

    @discardableResult
    func toggleDeveloperToolsFocusedBrowser() -> Bool {
        focusedBrowserPanel?.toggleDeveloperTools() ?? false
    }

    @discardableResult
    func showJavaScriptConsoleFocusedBrowser() -> Bool {
        focusedBrowserPanel?.showDeveloperToolsConsole() ?? false
    }

    func toggleReactGrabFocusedBrowser() {
        guard let panel = focusedBrowserPanel else { return }
        Task { await panel.toggleOrInjectReactGrab() }
    }

    /// Backwards compatibility: returns the focused surface ID
    func focusedSurfaceId(for tabId: UUID) -> UUID? {
        focusedPanelId(for: tabId)
    }

    func rememberFocusedSurface(tabId: UUID, surfaceId: UUID) {
        lastFocusedPanelByTab[tabId] = surfaceId
    }

    func applyWindowBackgroundForSelectedTab() {
        guard let selectedTabId,
              let tab = tabs.first(where: { $0.id == selectedTabId }),
              let terminalPanel = tab.focusedTerminalPanel else { return }
        terminalPanel.applyWindowBackgroundIfActive()
    }

    private func focusSelectedTabPanel(previousTabId: UUID?) {
        guard let selectedTabId,
              let tab = tabs.first(where: { $0.id == selectedTabId }) else { return }

        let panelId: UUID
        if let restoredPanelId = lastFocusedPanelByTab[selectedTabId],
           tab.panels[restoredPanelId] != nil {
            panelId = restoredPanelId
        } else if let focusedPanelId = tab.focusedPanelId,
                  tab.panels[focusedPanelId] != nil {
            panelId = focusedPanelId
        } else {
            return
        }

        // Defer unfocusing the previous workspace's panel until ContentView confirms handoff
        // completion (new workspace has focus or timeout fallback), to avoid a visible freeze gap.
        if let previousTabId,
           let previousTab = tabs.first(where: { $0.id == previousTabId }),
           let previousPanelId = previousTab.focusedPanelId,
           previousTab.panels[previousPanelId] != nil {
            replacePendingWorkspaceUnfocusTarget(
                with: (tabId: previousTabId, panelId: previousPanelId)
            )
        }

        // Route workspace reactivation through the normal focus machinery so panel-local
        // activation intents like browser find-field focus are restored on return.
        tab.focusPanel(panelId)
    }

    func completePendingWorkspaceUnfocus(reason: String) {
        guard let pending = pendingWorkspaceUnfocusTarget else { return }
        // If this tab became selected again before handoff completion, drop the stale
        // pending entry so it cannot be flushed later and deactivate the selected workspace.
        guard Self.shouldUnfocusPendingWorkspace(
            pendingTabId: pending.tabId,
            selectedTabId: selectedTabId
        ) else {
            pendingWorkspaceUnfocusTarget = nil
#if DEBUG
            dlog(
                "ws.unfocus.drop tab=\(Self.debugShortWorkspaceId(pending.tabId)) panel=\(String(pending.panelId.uuidString.prefix(5))) reason=selected_again"
            )
#endif
            return
        }
        pendingWorkspaceUnfocusTarget = nil
        unfocusWorkspacePanel(tabId: pending.tabId, panelId: pending.panelId)
#if DEBUG
        if let snapshot = debugCurrentWorkspaceSwitchSnapshot() {
            let dtMs = (CACurrentMediaTime() - snapshot.startedAt) * 1000
            dlog(
                "ws.unfocus.complete id=\(snapshot.id) dt=\(Self.debugMsText(dtMs)) " +
                "tab=\(Self.debugShortWorkspaceId(pending.tabId)) panel=\(String(pending.panelId.uuidString.prefix(5))) reason=\(reason)"
            )
        } else {
            dlog(
                "ws.unfocus.complete id=none tab=\(Self.debugShortWorkspaceId(pending.tabId)) " +
                "panel=\(String(pending.panelId.uuidString.prefix(5))) reason=\(reason)"
            )
        }
#endif
    }

    private func replacePendingWorkspaceUnfocusTarget(with next: (tabId: UUID, panelId: UUID)) {
        if let current = pendingWorkspaceUnfocusTarget,
           current.tabId == next.tabId,
           current.panelId == next.panelId {
            return
        }

        if let current = pendingWorkspaceUnfocusTarget {
            // Never unfocus the currently selected workspace when replacing stale pending state.
            if Self.shouldUnfocusPendingWorkspace(
                pendingTabId: current.tabId,
                selectedTabId: selectedTabId
            ) {
                unfocusWorkspacePanel(tabId: current.tabId, panelId: current.panelId)
#if DEBUG
                dlog(
                    "ws.unfocus.flush tab=\(Self.debugShortWorkspaceId(current.tabId)) panel=\(String(current.panelId.uuidString.prefix(5))) reason=replaced"
                )
#endif
            } else {
#if DEBUG
                dlog(
                    "ws.unfocus.drop tab=\(Self.debugShortWorkspaceId(current.tabId)) panel=\(String(current.panelId.uuidString.prefix(5))) reason=replaced_selected"
                )
#endif
            }
        }

        pendingWorkspaceUnfocusTarget = next
#if DEBUG
        if let snapshot = debugCurrentWorkspaceSwitchSnapshot() {
            let dtMs = (CACurrentMediaTime() - snapshot.startedAt) * 1000
            dlog(
                "ws.unfocus.defer id=\(snapshot.id) dt=\(Self.debugMsText(dtMs)) " +
                "tab=\(Self.debugShortWorkspaceId(next.tabId)) panel=\(String(next.panelId.uuidString.prefix(5)))"
            )
        } else {
            dlog(
                "ws.unfocus.defer id=none tab=\(Self.debugShortWorkspaceId(next.tabId)) panel=\(String(next.panelId.uuidString.prefix(5)))"
            )
        }
#endif
    }

    private func unfocusWorkspacePanel(tabId: UUID, panelId: UUID) {
        guard let tab = tabs.first(where: { $0.id == tabId }),
              let panel = tab.panels[panelId] else { return }
        panel.unfocus()
    }

    static func shouldUnfocusPendingWorkspace(pendingTabId: UUID, selectedTabId: UUID?) -> Bool {
        selectedTabId != pendingTabId
    }

    private func dismissFocusedPanelNotificationIfActive(tabId: UUID) {
        let shouldSuppressFlash = suppressFocusFlash
        suppressFocusFlash = false
        guard !shouldSuppressFlash else { return }
        guard AppFocusState.isAppActive() else { return }
        guard let panelId = focusedPanelId(for: tabId) else { return }
        dismissPanelNotificationOnFocusIfActive(tabId: tabId, panelId: panelId)
    }

    private func dismissPanelNotificationOnFocusIfActive(tabId: UUID, panelId: UUID) {
        guard selectedTabId == tabId else { return }
        guard !suppressFocusFlash else { return }
        guard AppFocusState.isAppActive() else { return }
        _ = dismissNotificationOnDirectInteraction(tabId: tabId, surfaceId: panelId)
    }

    @discardableResult
    func dismissNotificationOnDirectInteraction(tabId: UUID, surfaceId: UUID?) -> Bool {
        guard selectedTabId == tabId else { return false }
        guard AppFocusState.isAppActive() else { return false }
        guard let notificationStore = AppDelegate.shared?.notificationStore else { return false }
        let hasUnreadNotification = notificationStore.hasUnreadNotification(forTabId: tabId, surfaceId: surfaceId)
        let hasFocusedIndicator = notificationStore.hasVisibleNotificationIndicator(forTabId: tabId, surfaceId: surfaceId)
        guard hasUnreadNotification || hasFocusedIndicator else { return false }
        if hasUnreadNotification {
            notificationStore.markRead(forTabId: tabId, surfaceId: surfaceId)
        }
        notificationStore.clearFocusedReadIndicator(forTabId: tabId, surfaceId: surfaceId)
        if let panelId = surfaceId,
           let tab = tabs.first(where: { $0.id == tabId }) {
            tab.triggerNotificationDismissFlash(panelId: panelId)
        }
        return true
    }

    private func enqueuePanelTitleUpdate(tabId: UUID, panelId: UUID, title: String) {
        let trimmed = title.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !trimmed.isEmpty else { return }
        let key = PanelTitleUpdateKey(tabId: tabId, panelId: panelId)
        pendingPanelTitleUpdates[key] = trimmed
        panelTitleUpdateCoalescer.signal { [weak self] in
            self?.flushPendingPanelTitleUpdates()
        }
    }

    private func flushPendingPanelTitleUpdates() {
        guard !pendingPanelTitleUpdates.isEmpty else { return }
        let updates = pendingPanelTitleUpdates
        pendingPanelTitleUpdates.removeAll(keepingCapacity: true)
        for (key, title) in updates {
            updatePanelTitle(tabId: key.tabId, panelId: key.panelId, title: title)
        }
    }

    private func updatePanelTitle(tabId: UUID, panelId: UUID, title: String) {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return }
        let didChange = tab.updatePanelTitle(panelId: panelId, title: title)
        guard didChange else { return }

        // Update window title if this is the selected tab and focused panel
        if selectedTabId == tabId && tab.focusedPanelId == panelId {
            updateWindowTitle(for: tab)
        }
    }

    func focusedSurfaceTitleDidChange(tabId: UUID) {
        guard let tab = tabs.first(where: { $0.id == tabId }),
              let focusedPanelId = tab.focusedPanelId,
              let title = tab.panelTitles[focusedPanelId] else { return }
        tab.applyProcessTitle(title)
        if selectedTabId == tabId {
            updateWindowTitle(for: tab)
        }
    }

    private func updateWindowTitleForSelectedTab() {
        guard let selectedTabId,
              let tab = tabs.first(where: { $0.id == selectedTabId }) else {
            updateWindowTitle(for: nil)
            return
        }
        updateWindowTitle(for: tab)
    }

    private func updateWindowTitle(for tab: Workspace?) {
        let title = windowTitle(for: tab)
        guard let targetWindow = window else { return }
        targetWindow.title = title
    }

    private func windowTitle(for tab: Workspace?) -> String {
        guard let tab else { return "cmux" }
        let trimmedTitle = tab.title.trimmingCharacters(in: .whitespacesAndNewlines)
        if !trimmedTitle.isEmpty {
            return trimmedTitle
        }
        let trimmedDirectory = tab.currentDirectory.trimmingCharacters(in: .whitespacesAndNewlines)
        return trimmedDirectory.isEmpty ? "cmux" : trimmedDirectory
    }

    func focusTab(_ tabId: UUID, surfaceId: UUID? = nil, suppressFlash: Bool = false) {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return }
        if let surfaceId, tab.panels[surfaceId] != nil {
            // Keep selected-surface intent stable across selectedTabId didSet async restore.
            lastFocusedPanelByTab[tabId] = surfaceId
        }
#if DEBUG
        debugPrimeWorkspaceSwitchTrigger("focus", to: tabId)
#endif
        selectedTabId = tabId
        NotificationCenter.default.post(
            name: .ghosttyDidFocusTab,
            object: nil,
            userInfo: [GhosttyNotificationKey.tabId: tabId]
        )

        DispatchQueue.main.async { [weak self] in
            guard let self else { return }
            NSApp.activate(ignoringOtherApps: true)
            NSApp.unhide(nil)
            if let app = AppDelegate.shared,
               let windowId = app.windowId(for: self),
               let window = app.mainWindow(for: windowId) {
                window.makeKeyAndOrderFront(nil)
            } else if let window = NSApp.keyWindow ?? NSApp.windows.first {
                window.makeKeyAndOrderFront(nil)
            }
        }

        if let surfaceId {
            if !suppressFlash {
                focusSurface(tabId: tabId, surfaceId: surfaceId)
            } else {
                tab.focusPanel(surfaceId)
            }
        }
    }

    @discardableResult
    func focusTabFromNotification(_ tabId: UUID, surfaceId: UUID? = nil) -> Bool {
        guard let tab = tabs.first(where: { $0.id == tabId }) else {
#if DEBUG
            dlog("notification.focus.fail tab=\(tabId.uuidString.prefix(5)) reason=missingTab")
#endif
            return false
        }
        if let surfaceId, tab.panels[surfaceId] == nil {
#if DEBUG
            dlog(
                "notification.focus.fail tab=\(tabId.uuidString.prefix(5)) " +
                "panel=\(surfaceId.uuidString.prefix(5)) reason=missingPanel"
            )
#endif
            return false
        }
        let desiredPanelId = surfaceId ?? tab.focusedPanelId
#if DEBUG
        if let desiredPanelId {
            AppDelegate.shared?.armJumpUnreadFocusRecord(tabId: tabId, surfaceId: desiredPanelId)
        }
#endif
        // Jump-to-unread should reveal the destination pane instead of keeping an old split-zoom
        // state active around it.
        tab.clearSplitZoom()
        suppressFocusFlash = true
        focusTab(tabId, surfaceId: desiredPanelId, suppressFlash: true)
        suppressFocusFlash = false

        if let targetPanelId = desiredPanelId ?? tab.focusedPanelId,
           tab.panels[targetPanelId] != nil {
            _ = dismissNotificationOnDirectInteraction(tabId: tabId, surfaceId: targetPanelId)
        }
        return true
    }

    func focusSurface(tabId: UUID, surfaceId: UUID) {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return }
        tab.focusPanel(surfaceId)
    }

    func selectNextTab() {
        guard let currentId = selectedTabId,
              let currentIndex = tabs.firstIndex(where: { $0.id == currentId }) else { return }
        let nextIndex = (currentIndex + 1) % tabs.count
#if DEBUG
        let nextId = tabs[nextIndex].id
        debugPrepareWorkspaceSwitch("next", from: currentId, to: nextId)
#endif
        activateWorkspaceCycleHotWindow()
        selectedTabId = tabs[nextIndex].id
    }

    func selectPreviousTab() {
        guard let currentId = selectedTabId,
              let currentIndex = tabs.firstIndex(where: { $0.id == currentId }) else { return }
        let prevIndex = (currentIndex - 1 + tabs.count) % tabs.count
#if DEBUG
        let prevId = tabs[prevIndex].id
        debugPrepareWorkspaceSwitch("prev", from: currentId, to: prevId)
#endif
        activateWorkspaceCycleHotWindow()
        selectedTabId = tabs[prevIndex].id
    }

    private func activateWorkspaceCycleHotWindow() {
        workspaceCycleGeneration &+= 1
        let generation = workspaceCycleGeneration
#if DEBUG
        let switchId = debugWorkspaceSwitchId
        let switchDtMs = debugWorkspaceSwitchStartTime > 0
            ? (CACurrentMediaTime() - debugWorkspaceSwitchStartTime) * 1000
            : 0
#endif
        if !isWorkspaceCycleHot {
            isWorkspaceCycleHot = true
#if DEBUG
            dlog(
                "ws.hot.on id=\(switchId) gen=\(generation) dt=\(Self.debugMsText(switchDtMs))"
            )
#endif
        }

        let hadPendingCooldown = workspaceCycleCooldownTask != nil
        workspaceCycleCooldownTask?.cancel()
#if DEBUG
        if hadPendingCooldown {
            dlog(
                "ws.hot.cancelPrev id=\(switchId) gen=\(generation) dt=\(Self.debugMsText(switchDtMs))"
            )
        }
#endif
        workspaceCycleCooldownTask = Task { [weak self, generation] in
            do {
                try await Task.sleep(nanoseconds: 220_000_000)
            } catch {
#if DEBUG
                await MainActor.run {
                    guard let self else { return }
                    let dtMs = self.debugWorkspaceSwitchStartTime > 0
                        ? (CACurrentMediaTime() - self.debugWorkspaceSwitchStartTime) * 1000
                        : 0
                    dlog(
                        "ws.hot.cooldownCanceled id=\(self.debugWorkspaceSwitchId) gen=\(generation) dt=\(Self.debugMsText(dtMs))"
                    )
                }
#endif
                return
            }
            await MainActor.run {
                guard let self else { return }
                guard self.workspaceCycleGeneration == generation else { return }
#if DEBUG
                let dtMs = self.debugWorkspaceSwitchStartTime > 0
                    ? (CACurrentMediaTime() - self.debugWorkspaceSwitchStartTime) * 1000
                    : 0
                dlog(
                    "ws.hot.off id=\(self.debugWorkspaceSwitchId) gen=\(generation) dt=\(Self.debugMsText(dtMs))"
                )
#endif
                self.isWorkspaceCycleHot = false
                self.workspaceCycleCooldownTask = nil
            }
        }
    }

#if DEBUG
    func debugCurrentWorkspaceSwitchSnapshot() -> (id: UInt64, startedAt: CFTimeInterval)? {
        guard debugWorkspaceSwitchId > 0, debugWorkspaceSwitchStartTime > 0 else { return nil }
        return (debugWorkspaceSwitchId, debugWorkspaceSwitchStartTime)
    }

    private func debugPrimeWorkspaceSwitchTrigger(_ trigger: String, to target: UUID?) {
        guard selectedTabId != target else {
            debugPendingWorkspaceSwitchTrigger = nil
            debugPendingWorkspaceSwitchTarget = nil
            return
        }
        debugPendingWorkspaceSwitchTrigger = trigger
        debugPendingWorkspaceSwitchTarget = target
    }

    private func debugPrepareWorkspaceSwitch(_ trigger: String, from: UUID?, to: UUID?) {
        guard from != to else {
            debugPendingWorkspaceSwitchTrigger = nil
            debugPendingWorkspaceSwitchTarget = nil
            debugPreparedWorkspaceSwitchTarget = nil
            return
        }
        debugPendingWorkspaceSwitchTrigger = nil
        debugPendingWorkspaceSwitchTarget = nil
        debugBeginWorkspaceSwitch(trigger: trigger, from: from, to: to)
        debugPreparedWorkspaceSwitchTarget = to
    }

    private func debugBeginWorkspaceSwitch(trigger: String, from: UUID?, to: UUID?) {
        debugWorkspaceSwitchCounter &+= 1
        debugWorkspaceSwitchId = debugWorkspaceSwitchCounter
        debugWorkspaceSwitchStartTime = CACurrentMediaTime()
        dlog(
            "ws.switch.begin id=\(debugWorkspaceSwitchId) trigger=\(trigger) " +
            "from=\(Self.debugShortWorkspaceId(from)) to=\(Self.debugShortWorkspaceId(to)) " +
            "hot=\(isWorkspaceCycleHot ? 1 : 0) tabs=\(tabs.count)"
        )
    }

    private static func debugShortWorkspaceId(_ id: UUID?) -> String {
        guard let id else { return "nil" }
        return String(id.uuidString.prefix(5))
    }

    private static func debugMsText(_ ms: Double) -> String {
        String(format: "%.2fms", ms)
    }
#endif

    func selectTab(at index: Int) {
        guard index >= 0 && index < tabs.count else { return }
#if DEBUG
        debugPrimeWorkspaceSwitchTrigger("select_index", to: tabs[index].id)
#endif
        selectedTabId = tabs[index].id
    }

    func selectLastTab() {
        guard let lastTab = tabs.last else { return }
        selectedTabId = lastTab.id
    }

    // MARK: - Surface Navigation

    /// Select the next surface in the currently focused pane of the selected workspace
    func selectNextSurface() {
        selectedWorkspace?.selectNextSurface()
    }

    /// Select the previous surface in the currently focused pane of the selected workspace
    func selectPreviousSurface() {
        selectedWorkspace?.selectPreviousSurface()
    }

    /// Select a surface by index in the currently focused pane of the selected workspace
    func selectSurface(at index: Int) {
        selectedWorkspace?.selectSurface(at: index)
    }

    /// Select the last surface in the currently focused pane of the selected workspace
    func selectLastSurface() {
        selectedWorkspace?.selectLastSurface()
    }

    /// Create a new terminal surface in the focused pane of the selected workspace
    func newSurface() {
        // Cmd+T should always focus the newly created surface.
        selectedWorkspace?.clearSplitZoom()
        selectedWorkspace?.newTerminalSurfaceInFocusedPane(focus: true)
    }

    // MARK: - Split Creation

    /// Create a new split in the current tab
    @discardableResult
    func createSplit(direction: SplitDirection) -> UUID? {
        guard let selectedTabId,
              let tab = tabs.first(where: { $0.id == selectedTabId }),
              let focusedPanelId = tab.focusedPanelId else { return nil }
        return createSplit(tabId: selectedTabId, surfaceId: focusedPanelId, direction: direction)
    }

    /// Create a new split from an explicit source panel.
    @discardableResult
    func createSplit(tabId: UUID, surfaceId: UUID, direction: SplitDirection, focus: Bool = true) -> UUID? {
        guard let tab = tabs.first(where: { $0.id == tabId }),
              tab.panels[surfaceId] != nil else { return nil }
        tab.clearSplitZoom()
        sentryBreadcrumb("split.create", data: ["direction": String(describing: direction)])
        return newSplit(tabId: tabId, surfaceId: surfaceId, direction: direction, focus: focus)
    }

    /// Create a new browser split from the currently focused panel.
    @discardableResult
    func createBrowserSplit(direction: SplitDirection, url: URL? = nil) -> UUID? {
        guard let selectedTabId,
              let tab = tabs.first(where: { $0.id == selectedTabId }),
              let focusedPanelId = tab.focusedPanelId else { return nil }
        tab.clearSplitZoom()
        return newBrowserSplit(
            tabId: selectedTabId,
            fromPanelId: focusedPanelId,
            orientation: direction.orientation,
            insertFirst: direction.insertFirst,
            url: url
        )
    }

    /// Refresh Bonsplit right-side action button tooltips for all workspaces.
    func refreshSplitButtonTooltips() {
        for workspace in tabs {
            workspace.refreshSplitButtonTooltips()
        }
    }

    // MARK: - Pane Focus Navigation

    /// Move focus to an adjacent pane in the specified direction
    func movePaneFocus(direction: NavigationDirection) {
        guard let selectedTabId,
              let tab = tabs.first(where: { $0.id == selectedTabId }) else { return }
        tab.moveFocus(direction: direction)
    }

    // MARK: - Recent Tab History Navigation

    private func recordTabInHistory(_ tabId: UUID) {
        // If we're not at the end of history, truncate forward history
        if historyIndex < tabHistory.count - 1 {
            tabHistory = Array(tabHistory.prefix(historyIndex + 1))
        }

        // Don't add duplicate consecutive entries
        if tabHistory.last == tabId {
            return
        }

        tabHistory.append(tabId)

        // Trim history if it exceeds max size
        if tabHistory.count > maxHistorySize {
            tabHistory.removeFirst(tabHistory.count - maxHistorySize)
        }

        historyIndex = tabHistory.count - 1
    }

    func navigateBack() {
        guard historyIndex > 0 else { return }

        // Find the previous valid tab in history (skip closed tabs)
        var targetIndex = historyIndex - 1
        while targetIndex >= 0 {
            let tabId = tabHistory[targetIndex]
            if tabs.contains(where: { $0.id == tabId }) {
                isNavigatingHistory = true
                historyIndex = targetIndex
                selectedTabId = tabId
                isNavigatingHistory = false
                return
            }
            // Remove closed tab from history
            tabHistory.remove(at: targetIndex)
            historyIndex -= 1
            targetIndex -= 1
        }
    }

    func navigateForward() {
        guard historyIndex < tabHistory.count - 1 else { return }

        // Find the next valid tab in history (skip closed tabs)
        let targetIndex = historyIndex + 1
        while targetIndex < tabHistory.count {
            let tabId = tabHistory[targetIndex]
            if tabs.contains(where: { $0.id == tabId }) {
                isNavigatingHistory = true
                historyIndex = targetIndex
                selectedTabId = tabId
                isNavigatingHistory = false
                return
            }
            // Remove closed tab from history
            tabHistory.remove(at: targetIndex)
            // Don't increment targetIndex since we removed the element
        }
    }

    var canNavigateBack: Bool {
        historyIndex > 0 && tabHistory.prefix(historyIndex).contains { tabId in
            tabs.contains { $0.id == tabId }
        }
    }

    var canNavigateForward: Bool {
        historyIndex < tabHistory.count - 1 && tabHistory.suffix(from: historyIndex + 1).contains { tabId in
            tabs.contains { $0.id == tabId }
        }
    }

    // MARK: - Split Operations (Backwards Compatibility)

    /// Create a new split in the specified direction
    /// Returns the new panel's ID (which is also the surface ID for terminals)
    func newSplit(tabId: UUID, surfaceId: UUID, direction: SplitDirection, focus: Bool = true) -> UUID? {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return nil }
        return tab.newTerminalSplit(
            from: surfaceId,
            orientation: direction.orientation,
            insertFirst: direction.insertFirst,
            focus: focus
        )?.id
    }

    /// Move focus in the specified direction
    func moveSplitFocus(tabId: UUID, surfaceId: UUID, direction: NavigationDirection) -> Bool {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return false }
        tab.moveFocus(direction: direction)
        return true
    }

    /// Resize split - not directly supported by bonsplit, but we can adjust divider positions
    func resizeSplit(tabId: UUID, surfaceId: UUID, direction: ResizeDirection, amount: UInt16) -> Bool {
        guard amount > 0,
              let tab = tabs.first(where: { $0.id == tabId }),
              let paneId = tab.paneId(forPanelId: surfaceId) else { return false }

        let paneUUID = paneId.id
        guard tab.bonsplitController.allPaneIds.contains(where: { $0.id == paneUUID }) else {
            return false
        }

        var candidates: [ResizeSplitCandidate] = []
        let trace = resizeSplitCollectCandidates(
            node: tab.bonsplitController.treeSnapshot(),
            targetPaneId: paneUUID.uuidString,
            candidates: &candidates
        )
        guard trace.containsTarget else { return false }

        let orientationMatches = candidates.filter { $0.orientation == direction.splitOrientation }
        guard !orientationMatches.isEmpty else { return false }

        guard let candidate = orientationMatches.first(where: {
            $0.paneInFirstChild == direction.requiresPaneInFirstChild
        }) else {
            return false
        }

        let delta = CGFloat(amount) / candidate.axisPixels
        let requested = candidate.dividerPosition + (direction.dividerDeltaSign * delta)
        let clamped = min(max(requested, 0.1), 0.9)
        return tab.bonsplitController.setDividerPosition(clamped, forSplit: candidate.splitId, fromExternal: true)
    }

    /// Equalize splits - not directly supported by bonsplit
    func equalizeSplits(tabId: UUID) -> Bool {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return false }

        var foundSplit = false
        var allSucceeded = true
        equalizeSplits(
            in: tab.bonsplitController.treeSnapshot(),
            controller: tab.bonsplitController,
            foundSplit: &foundSplit,
            allSucceeded: &allSucceeded
        )
        return foundSplit && allSucceeded
    }

    /// Toggle zoom on a panel.
    func toggleSplitZoom(tabId: UUID, surfaceId: UUID) -> Bool {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return false }
        return tab.toggleSplitZoom(panelId: surfaceId)
    }

    /// Toggle zoom for the currently focused panel in the selected workspace.
    @discardableResult
    func toggleFocusedSplitZoom() -> Bool {
        guard let tab = selectedWorkspace,
              let focusedPanelId = tab.focusedPanelId else { return false }
        return tab.toggleSplitZoom(panelId: focusedPanelId)
    }

    private func equalizeSplits(
        in node: ExternalTreeNode,
        controller: BonsplitController,
        foundSplit: inout Bool,
        allSucceeded: inout Bool
    ) {
        switch node {
        case .pane:
            return
        case .split(let splitNode):
            foundSplit = true
            guard let splitId = UUID(uuidString: splitNode.id) else {
                allSucceeded = false
                return
            }

            if !controller.setDividerPosition(0.5, forSplit: splitId) {
                allSucceeded = false
            }

            equalizeSplits(
                in: splitNode.first,
                controller: controller,
                foundSplit: &foundSplit,
                allSucceeded: &allSucceeded
            )
            equalizeSplits(
                in: splitNode.second,
                controller: controller,
                foundSplit: &foundSplit,
                allSucceeded: &allSucceeded
            )
        }
    }

    private struct ResizeSplitCandidate {
        let splitId: UUID
        let orientation: String
        let paneInFirstChild: Bool
        let dividerPosition: CGFloat
        let axisPixels: CGFloat
    }

    private struct ResizeSplitTrace {
        let containsTarget: Bool
        let bounds: CGRect
    }

    private func resizeSplitCollectCandidates(
        node: ExternalTreeNode,
        targetPaneId: String,
        candidates: inout [ResizeSplitCandidate]
    ) -> ResizeSplitTrace {
        switch node {
        case .pane(let pane):
            let bounds = CGRect(
                x: pane.frame.x,
                y: pane.frame.y,
                width: pane.frame.width,
                height: pane.frame.height
            )
            return ResizeSplitTrace(containsTarget: pane.id == targetPaneId, bounds: bounds)

        case .split(let split):
            let first = resizeSplitCollectCandidates(
                node: split.first,
                targetPaneId: targetPaneId,
                candidates: &candidates
            )
            let second = resizeSplitCollectCandidates(
                node: split.second,
                targetPaneId: targetPaneId,
                candidates: &candidates
            )

            let combinedBounds = first.bounds.union(second.bounds)
            let containsTarget = first.containsTarget || second.containsTarget

            if containsTarget,
               let splitUUID = UUID(uuidString: split.id) {
                let orientation = split.orientation.lowercased()
                let axisPixels: CGFloat = orientation == "horizontal"
                    ? combinedBounds.width
                    : combinedBounds.height
                candidates.append(ResizeSplitCandidate(
                    splitId: splitUUID,
                    orientation: orientation,
                    paneInFirstChild: first.containsTarget,
                    dividerPosition: CGFloat(split.dividerPosition),
                    axisPixels: max(axisPixels, 1)
                ))
            }

            return ResizeSplitTrace(containsTarget: containsTarget, bounds: combinedBounds)
        }
    }

    /// Close a surface/panel
    func closeSurface(tabId: UUID, surfaceId: UUID) -> Bool {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return false }
        // Guard against stale close callbacks (e.g. child-exit can trigger multiple actions).
        // A stale callback must never affect unrelated panels/workspaces.
        guard tab.panels[surfaceId] != nil,
              tab.surfaceIdFromPanelId(surfaceId) != nil else { return false }
        tab.closePanel(surfaceId)
        AppDelegate.shared?.notificationStore?.clearNotifications(forTabId: tabId, surfaceId: surfaceId)
        return true
    }

    // MARK: - Browser Panel Operations

    /// Create a new browser panel in a split
    func newBrowserSplit(
        tabId: UUID,
        fromPanelId: UUID,
        orientation: SplitOrientation,
        insertFirst: Bool = false,
        url: URL? = nil,
        preferredProfileID: UUID? = nil,
        focus: Bool = true
    ) -> UUID? {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return nil }
        return tab.newBrowserSplit(
            from: fromPanelId,
            orientation: orientation,
            insertFirst: insertFirst,
            url: url,
            preferredProfileID: preferredProfileID,
            focus: focus
        )?.id
    }

    /// Create a new browser surface in a pane
    func newBrowserSurface(
        tabId: UUID,
        inPane paneId: PaneID,
        url: URL? = nil,
        preferredProfileID: UUID? = nil
    ) -> UUID? {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return nil }
        return tab.newBrowserSurface(
            inPane: paneId,
            url: url,
            preferredProfileID: preferredProfileID
        )?.id
    }

    /// Get a browser panel by ID
    func browserPanel(tabId: UUID, panelId: UUID) -> BrowserPanel? {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return nil }
        return tab.browserPanel(for: panelId)
    }

    /// Open a browser in a specific workspace, optionally preferring a split-right layout.
    @discardableResult
    func openBrowser(
        inWorkspace tabId: UUID,
        url: URL? = nil,
        preferSplitRight: Bool = false,
        preferredProfileID: UUID? = nil,
        insertAtEnd: Bool = false
    ) -> UUID? {
        guard let workspace = tabs.first(where: { $0.id == tabId }) else { return nil }
        if selectedTabId != tabId {
            selectedTabId = tabId
        }

        if preferSplitRight {
            if let targetPaneId = workspace.topRightBrowserReusePane(),
               let browserPanel = workspace.newBrowserSurface(
                   inPane: targetPaneId,
                   url: url,
                   focus: true,
                   insertAtEnd: insertAtEnd,
                   preferredProfileID: preferredProfileID
               ) {
                rememberFocusedSurface(tabId: tabId, surfaceId: browserPanel.id)
                return browserPanel.id
            }

            let splitSourcePanelId: UUID? = {
                if let focusedPanelId = workspace.focusedPanelId,
                   workspace.panels[focusedPanelId] != nil {
                    return focusedPanelId
                }
                if let rememberedPanelId = lastFocusedPanelByTab[tabId],
                   workspace.panels[rememberedPanelId] != nil {
                    return rememberedPanelId
                }
                if let orderedPanelId = workspace.sidebarOrderedPanelIds().first(where: { workspace.panels[$0] != nil }) {
                    return orderedPanelId
                }
                return workspace.panels.keys.sorted { $0.uuidString < $1.uuidString }.first
            }()

            if let splitSourcePanelId,
               let browserPanel = workspace.newBrowserSplit(
                   from: splitSourcePanelId,
                   orientation: .horizontal,
                   url: url,
                   preferredProfileID: preferredProfileID,
                   focus: true
               ) {
                rememberFocusedSurface(tabId: tabId, surfaceId: browserPanel.id)
                return browserPanel.id
            }
        }

        guard let paneId = workspace.bonsplitController.focusedPaneId ?? workspace.bonsplitController.allPaneIds.first,
              let browserPanel = workspace.newBrowserSurface(
                  inPane: paneId,
                  url: url,
                  focus: true,
                  insertAtEnd: insertAtEnd,
                  preferredProfileID: preferredProfileID
              ) else {
            return nil
        }
        rememberFocusedSurface(tabId: tabId, surfaceId: browserPanel.id)
        return browserPanel.id
    }

    /// Open a browser in the currently focused pane (as a new surface)
    @discardableResult
    func openBrowser(
        url: URL? = nil,
        preferredProfileID: UUID? = nil,
        insertAtEnd: Bool = false
    ) -> UUID? {
        guard let tabId = selectedTabId else { return nil }
        return openBrowser(
            inWorkspace: tabId,
            url: url,
            preferSplitRight: false,
            preferredProfileID: preferredProfileID,
            insertAtEnd: insertAtEnd
        )
    }

    /// Reopen the most recently closed browser panel (Cmd+Shift+T).
    /// No-op when no browser panel restore snapshot is available.
    @discardableResult
    func reopenMostRecentlyClosedBrowserPanel() -> Bool {
        while let snapshot = recentlyClosedBrowsers.pop() {
            guard let targetWorkspace =
                tabs.first(where: { $0.id == snapshot.workspaceId })
                ?? selectedWorkspace
                ?? tabs.first else {
                return false
            }
            let preReopenFocusedPanelId = focusedPanelId(for: targetWorkspace.id)

            if selectedTabId != targetWorkspace.id {
                selectedTabId = targetWorkspace.id
            }

            if let reopenedPanelId = reopenClosedBrowserPanel(snapshot, in: targetWorkspace) {
                enforceReopenedBrowserFocus(
                    tabId: targetWorkspace.id,
                    reopenedPanelId: reopenedPanelId,
                    preReopenFocusedPanelId: preReopenFocusedPanelId
                )
                return true
            }
        }

        return false
    }

    private func enforceReopenedBrowserFocus(
        tabId: UUID,
        reopenedPanelId: UUID,
        preReopenFocusedPanelId: UUID?
    ) {
        // Keep workspace-switch restoration pinned to the reopened browser panel.
        rememberFocusedSurface(tabId: tabId, surfaceId: reopenedPanelId)
        enforceReopenedBrowserFocusIfNeeded(
            tabId: tabId,
            reopenedPanelId: reopenedPanelId,
            preReopenFocusedPanelId: preReopenFocusedPanelId
        )

        // Some stale focus callbacks can land one runloop turn later. Re-assert focus in two
        // consecutive turns, but only when focus drifted back to the pre-reopen panel.
        DispatchQueue.main.async { [weak self] in
            guard let self else { return }
            self.enforceReopenedBrowserFocusIfNeeded(
                tabId: tabId,
                reopenedPanelId: reopenedPanelId,
                preReopenFocusedPanelId: preReopenFocusedPanelId
            )
            DispatchQueue.main.async { [weak self] in
                self?.enforceReopenedBrowserFocusIfNeeded(
                    tabId: tabId,
                    reopenedPanelId: reopenedPanelId,
                    preReopenFocusedPanelId: preReopenFocusedPanelId
                )
            }
        }
    }

    private func enforceReopenedBrowserFocusIfNeeded(
        tabId: UUID,
        reopenedPanelId: UUID,
        preReopenFocusedPanelId: UUID?
    ) {
        guard selectedTabId == tabId,
              let tab = tabs.first(where: { $0.id == tabId }),
              tab.panels[reopenedPanelId] != nil else {
            return
        }

        rememberFocusedSurface(tabId: tabId, surfaceId: reopenedPanelId)

        guard tab.focusedPanelId != reopenedPanelId else { return }

        if let focusedPanelId = tab.focusedPanelId,
           let preReopenFocusedPanelId,
           focusedPanelId != preReopenFocusedPanelId {
            return
        }

        tab.focusPanel(reopenedPanelId)
    }

    private func reopenClosedBrowserPanel(
        _ snapshot: ClosedBrowserPanelRestoreSnapshot,
        in workspace: Workspace
    ) -> UUID? {
        if let originalPane = workspace.bonsplitController.allPaneIds.first(where: { $0.id == snapshot.originalPaneId }),
           let browserPanel = workspace.newBrowserSurface(
               inPane: originalPane,
               url: snapshot.url,
               focus: true,
               preferredProfileID: snapshot.profileID
           ) {
            let tabCount = workspace.bonsplitController.tabs(inPane: originalPane).count
            let maxIndex = max(0, tabCount - 1)
            let targetIndex = min(max(snapshot.originalTabIndex, 0), maxIndex)
            _ = workspace.reorderSurface(panelId: browserPanel.id, toIndex: targetIndex)
            return browserPanel.id
        }

        if let orientation = snapshot.fallbackSplitOrientation,
           let fallbackAnchorPaneId = snapshot.fallbackAnchorPaneId,
           let anchorPane = workspace.bonsplitController.allPaneIds.first(where: { $0.id == fallbackAnchorPaneId }),
           let anchorTab = workspace.bonsplitController.selectedTab(inPane: anchorPane) ?? workspace.bonsplitController.tabs(inPane: anchorPane).first,
           let anchorPanelId = workspace.panelIdFromSurfaceId(anchorTab.id),
           let browserPanelId = workspace.newBrowserSplit(
               from: anchorPanelId,
               orientation: orientation,
               insertFirst: snapshot.fallbackSplitInsertFirst,
               url: snapshot.url,
               preferredProfileID: snapshot.profileID
           )?.id {
            return browserPanelId
        }

        guard let focusedPane = workspace.bonsplitController.focusedPaneId ?? workspace.bonsplitController.allPaneIds.first else {
            return nil
        }
        return workspace.newBrowserSurface(
            inPane: focusedPane,
            url: snapshot.url,
            focus: true,
            preferredProfileID: snapshot.profileID
        )?.id
    }

    /// Flash the currently focused panel so the user can visually confirm focus.
    func triggerFocusFlash() {
        guard let tab = selectedWorkspace,
              let panelId = tab.focusedPanelId else { return }
        tab.triggerFocusFlash(panelId: panelId)
    }

    /// Ensure AppKit first responder matches the currently focused terminal panel.
    /// This keeps real keyboard events (including Ctrl+D) on the same panel as the
    /// bonsplit focus indicator after rapid split topology changes.
    func ensureFocusedTerminalFirstResponder() {
        guard let tab = selectedWorkspace,
              let panelId = tab.focusedPanelId,
              let terminal = tab.terminalPanel(for: panelId) else { return }
        terminal.hostedView.ensureFocus(for: tab.id, surfaceId: panelId)
    }

    /// Reconcile keyboard routing before terminal control shortcuts (e.g. Ctrl+D).
    ///
    /// Source of truth for pane focus is bonsplit's focused pane + selected tab.
    /// Keyboard delivery must converge AppKit first responder to that model state, not mutate
    /// the model from whatever first responder happened to be during reparenting transitions.
    func reconcileFocusedPanelFromFirstResponderForKeyboard() {
        ensureFocusedTerminalFirstResponder()
    }

    /// Get a terminal panel by ID
    func terminalPanel(tabId: UUID, panelId: UUID) -> TerminalPanel? {
        guard let tab = tabs.first(where: { $0.id == tabId }) else { return nil }
        return tab.terminalPanel(for: panelId)
    }

    /// Get the panel for a surface ID (terminal panels use surface ID as panel ID)
    func surface(for tabId: UUID, surfaceId: UUID) -> TerminalSurface? {
        terminalPanel(tabId: tabId, panelId: surfaceId)?.surface
    }

#if DEBUG
    @MainActor
    private func waitForWorkspacePanelsCondition(
        tab: Workspace,
        timeoutSeconds: TimeInterval,
        condition: @escaping (Workspace) -> Bool
    ) async -> Bool {
        guard !condition(tab) else { return true }

        return await withCheckedContinuation { (cont: CheckedContinuation<Bool, Never>) in
            var resolved = false
            var cancellable: AnyCancellable?

            func finish(_ value: Bool) {
                guard !resolved else { return }
                resolved = true
                cancellable?.cancel()
                cont.resume(returning: value)
            }

            func evaluate() {
                if condition(tab) {
                    finish(true)
                }
            }

            cancellable = tab.$panels
                .map { _ in () }
                .sink { _ in evaluate() }

            DispatchQueue.main.asyncAfter(deadline: .now() + timeoutSeconds) {
                Task { @MainActor in
                    finish(condition(tab))
                }
            }
            evaluate()
        }
    }

    @MainActor
    private func waitForTerminalPanelCondition(
        tab: Workspace,
        panelId: UUID,
        timeoutSeconds: TimeInterval,
        condition: @escaping (TerminalPanel) -> Bool
    ) async -> Bool {
        if let panel = tab.terminalPanel(for: panelId), condition(panel) {
            return true
        }

        return await withCheckedContinuation { (cont: CheckedContinuation<Bool, Never>) in
            var resolved = false
            var panelsCancellable: AnyCancellable?
            var readyObserver: NSObjectProtocol?
            var hostedViewObserver: NSObjectProtocol?

            @MainActor
            func finish(_ value: Bool) {
                guard !resolved else { return }
                resolved = true
                panelsCancellable?.cancel()
                if let readyObserver {
                    NotificationCenter.default.removeObserver(readyObserver)
                }
                if let hostedViewObserver {
                    NotificationCenter.default.removeObserver(hostedViewObserver)
                }
                cont.resume(returning: value)
            }

            @MainActor
            func evaluate() {
                guard let panel = tab.terminalPanel(for: panelId) else {
                    finish(false)
                    return
                }
                panel.surface.requestBackgroundSurfaceStartIfNeeded()
                if condition(panel) {
                    finish(true)
                }
            }

            panelsCancellable = tab.$panels
                .map { _ in () }
                .sink { _ in
                    Task { @MainActor in
                        evaluate()
                    }
                }
            readyObserver = NotificationCenter.default.addObserver(
                forName: .terminalSurfaceDidBecomeReady,
                object: nil,
                queue: .main
            ) { note in
                guard let readySurfaceId = note.userInfo?["surfaceId"] as? UUID,
                      readySurfaceId == panelId else { return }
                Task { @MainActor in
                    evaluate()
                }
            }
            hostedViewObserver = NotificationCenter.default.addObserver(
                forName: .terminalSurfaceHostedViewDidMoveToWindow,
                object: nil,
                queue: .main
            ) { note in
                guard let hostedSurfaceId = note.userInfo?["surfaceId"] as? UUID,
                      hostedSurfaceId == panelId else { return }
                Task { @MainActor in
                    evaluate()
                }
            }

            DispatchQueue.main.asyncAfter(deadline: .now() + timeoutSeconds) {
                Task { @MainActor in
                    if let panel = tab.terminalPanel(for: panelId) {
                        finish(condition(panel))
                    } else {
                        finish(false)
                    }
                }
            }
            evaluate()
        }
    }

    @MainActor
    private func waitForTerminalPanelReadyForUITest(
        tab: Workspace,
        panelId: UUID,
        timeoutSeconds: TimeInterval = 6.0
    ) async -> (attached: Bool, hasSurface: Bool, firstResponder: Bool) {
        var attached = false
        var hasSurface = false
        var firstResponder = false

        let _ = await waitForTerminalPanelCondition(
            tab: tab,
            panelId: panelId,
            timeoutSeconds: timeoutSeconds
        ) { panel in
            panel.surface.requestBackgroundSurfaceStartIfNeeded()
            attached = panel.hostedView.window != nil
            hasSurface = panel.surface.surface != nil
            firstResponder = panel.hostedView.isSurfaceViewFirstResponder()
            return attached && hasSurface
        }

        return (attached, hasSurface, firstResponder)
    }

    private func setupUITestFocusShortcutsIfNeeded() {
        guard !didSetupUITestFocusShortcuts else { return }
        didSetupUITestFocusShortcuts = true

        let env = ProcessInfo.processInfo.environment
        guard env["CMUX_UI_TEST_FOCUS_SHORTCUTS"] == "1" else { return }

        // UI tests can't record arrow keys via the shortcut recorder. Use letter-based shortcuts
        // so tests can reliably drive pane navigation without mouse clicks.
        KeyboardShortcutSettings.setShortcut(
            StoredShortcut(key: "h", command: true, shift: false, option: false, control: true),
            for: .focusLeft
        )
        KeyboardShortcutSettings.setShortcut(
            StoredShortcut(key: "l", command: true, shift: false, option: false, control: true),
            for: .focusRight
        )
        KeyboardShortcutSettings.setShortcut(
            StoredShortcut(key: "k", command: true, shift: false, option: false, control: true),
            for: .focusUp
        )
        KeyboardShortcutSettings.setShortcut(
            StoredShortcut(key: "j", command: true, shift: false, option: false, control: true),
            for: .focusDown
        )
    }

    private func setupSplitCloseRightUITestIfNeeded() {
        guard !didSetupSplitCloseRightUITest else { return }
        didSetupSplitCloseRightUITest = true

        let env = ProcessInfo.processInfo.environment
        guard env["CMUX_UI_TEST_SPLIT_CLOSE_RIGHT_SETUP"] == "1" else { return }
        guard let path = env["CMUX_UI_TEST_SPLIT_CLOSE_RIGHT_PATH"], !path.isEmpty else { return }
        let visualMode = env["CMUX_UI_TEST_SPLIT_CLOSE_RIGHT_VISUAL"] == "1"
        let shotsDir = (env["CMUX_UI_TEST_SPLIT_CLOSE_RIGHT_SHOTS_DIR"] ?? "").trimmingCharacters(in: .whitespacesAndNewlines)
        let visualIterations = Int((env["CMUX_UI_TEST_SPLIT_CLOSE_RIGHT_ITERATIONS"] ?? "20").trimmingCharacters(in: .whitespacesAndNewlines)) ?? 20
        let burstFrames = Int((env["CMUX_UI_TEST_SPLIT_CLOSE_RIGHT_BURST_FRAMES"] ?? "6").trimmingCharacters(in: .whitespacesAndNewlines)) ?? 6
        let closeDelayMs = Int((env["CMUX_UI_TEST_SPLIT_CLOSE_RIGHT_CLOSE_DELAY_MS"] ?? "70").trimmingCharacters(in: .whitespacesAndNewlines)) ?? 70
        let pattern = (env["CMUX_UI_TEST_SPLIT_CLOSE_RIGHT_PATTERN"] ?? "close_right")
            .trimmingCharacters(in: .whitespacesAndNewlines)

        DispatchQueue.main.asyncAfter(deadline: .now() + 0.2) { [weak self] in
            guard let self else { return }
            Task { @MainActor [weak self] in
                guard let self else { return }
                guard let tab = self.selectedWorkspace else {
                    self.writeSplitCloseRightTestData(["setupError": "Missing selected workspace"], at: path)
                    return
                }

                guard let topLeftPanelId = tab.focusedPanelId else {
                    self.writeSplitCloseRightTestData(["setupError": "Missing initial focused panel"], at: path)
                    return
                }
                let initialTerminalReadiness = await self.waitForTerminalPanelReadyForUITest(
                    tab: tab,
                    panelId: topLeftPanelId
                )

                guard initialTerminalReadiness.attached,
                      initialTerminalReadiness.hasSurface,
                      let terminal = tab.terminalPanel(for: topLeftPanelId) else {
                    self.writeSplitCloseRightTestData([
                        "preTerminalAttached": initialTerminalReadiness.attached ? "1" : "0",
                        "preTerminalSurfaceNil": initialTerminalReadiness.hasSurface ? "0" : "1",
                        "setupError": "Initial terminal not ready (not attached or surface nil)"
                    ], at: path)
                    return
                }

                self.writeSplitCloseRightTestData([
                    "preTerminalAttached": "1",
                    "preTerminalSurfaceNil": terminal.surface.surface == nil ? "1" : "0"
                ], at: path)

                if visualMode {
                    // Visual repro mode: repeat the split/close sequence many times and write
                    // screenshots to `shotsDir`. This avoids relying on XCUITest to click hover-only
                    // close buttons, while still exercising the "close unfocused right tabs" path.
                    self.writeSplitCloseRightTestData([
                        "visualMode": "1",
                        "visualIterations": String(visualIterations),
                        "visualDone": "0"
                    ], at: path)

                    await self.runSplitCloseRightVisualRepro(
                        tab: tab,
                        topLeftPanelId: topLeftPanelId,
                        path: path,
                        shotsDir: shotsDir,
                        iterations: max(1, min(visualIterations, 60)),
                        burstFrames: max(0, min(burstFrames, 80)),
                        closeDelayMs: max(0, min(closeDelayMs, 500)),
                        pattern: pattern
                    )

                    self.writeSplitCloseRightTestData(["visualDone": "1"], at: path)
                    return
                }

                // Layout goal: 2x2 grid (2 top, 2 bottom), then close both right panels.
                // Order matters: split down first, then split right in each row (matches UI shortcut repro).
                guard let bottomLeft = tab.newTerminalSplit(from: topLeftPanelId, orientation: .vertical) else {
                    self.writeSplitCloseRightTestData(["setupError": "Failed to create bottom-left split"], at: path)
                    return
                }
                guard let bottomRight = tab.newTerminalSplit(from: bottomLeft.id, orientation: .horizontal) else {
                    self.writeSplitCloseRightTestData(["setupError": "Failed to create bottom-right split"], at: path)
                    return
                }
                tab.focusPanel(topLeftPanelId)
                guard let topRight = tab.newTerminalSplit(from: topLeftPanelId, orientation: .horizontal) else {
                    self.writeSplitCloseRightTestData(["setupError": "Failed to create top-right split"], at: path)
                    return
                }

                self.writeSplitCloseRightTestData([
                    "tabId": tab.id.uuidString,
                    "topLeftPanelId": topLeftPanelId.uuidString,
                    "bottomLeftPanelId": bottomLeft.id.uuidString,
                    "topRightPanelId": topRight.id.uuidString,
                    "bottomRightPanelId": bottomRight.id.uuidString,
                    "createdPaneCount": String(tab.bonsplitController.allPaneIds.count),
                    "createdPanelCount": String(tab.panels.count)
                ], at: path)

                DebugUIEventCounters.resetEmptyPanelAppearCount()

                // Close the two right panes via the same path as Cmd+W.
                tab.focusPanel(topRight.id)
                tab.closePanel(topRight.id, force: true)
                tab.focusPanel(bottomRight.id)
                tab.closePanel(bottomRight.id, force: true)


                // Capture final state after Bonsplit/AppKit/Ghostty geometry reconciliation.
                // We avoid sleep-based timing and converge over a few main-actor turns.
                 @MainActor func collectSplitCloseRightState() -> (data: [String: String], settled: Bool) {
                    let paneIds = tab.bonsplitController.allPaneIds
                    let bonsplitTabCount = tab.bonsplitController.allTabIds.count
                    let panelCount = tab.panels.count

                    var missingSelectedTabCount = 0
                    var missingPanelMappingCount = 0
                    var selectedTerminalCount = 0
                    var selectedTerminalAttachedCount = 0
                    var selectedTerminalZeroSizeCount = 0
                    var selectedTerminalSurfaceNilCount = 0

                    for paneId in paneIds {
                        guard let selected = tab.bonsplitController.selectedTab(inPane: paneId) else {
                            missingSelectedTabCount += 1
                            continue
                        }
                        guard let panel = tab.panel(for: selected.id) else {
                            missingPanelMappingCount += 1
                            continue
                        }
                        if let terminal = panel as? TerminalPanel {
                            selectedTerminalCount += 1
                            if terminal.hostedView.window != nil {
                                selectedTerminalAttachedCount += 1
                            }
                            let size = terminal.hostedView.bounds.size
                            if size.width < 5 || size.height < 5 {
                                selectedTerminalZeroSizeCount += 1
                            }
                            if terminal.surface.surface == nil {
                                selectedTerminalSurfaceNilCount += 1
                            }
                        }
                    }

                    let settled =
                        paneIds.count == 2 &&
                        missingSelectedTabCount == 0 &&
                        missingPanelMappingCount == 0 &&
                        DebugUIEventCounters.emptyPanelAppearCount == 0 &&
                        selectedTerminalCount == 2 &&
                        selectedTerminalAttachedCount == 2 &&
                        selectedTerminalZeroSizeCount == 0 &&
                        selectedTerminalSurfaceNilCount == 0

                    return (
                        data: [
                            "finalPaneCount": String(paneIds.count),
                            "finalBonsplitTabCount": String(bonsplitTabCount),
                            "finalPanelCount": String(panelCount),
                            "missingSelectedTabCount": String(missingSelectedTabCount),
                            "missingPanelMappingCount": String(missingPanelMappingCount),
                            "emptyPanelAppearCount": String(DebugUIEventCounters.emptyPanelAppearCount),
                            "selectedTerminalCount": String(selectedTerminalCount),
                            "selectedTerminalAttachedCount": String(selectedTerminalAttachedCount),
                            "selectedTerminalZeroSizeCount": String(selectedTerminalZeroSizeCount),
                            "selectedTerminalSurfaceNilCount": String(selectedTerminalSurfaceNilCount),
                        ],
                        settled: settled
                    )
                }
                 @MainActor func reconcileVisibleTerminalGeometry() {
                    NSApp.windows.forEach { window in
                        window.contentView?.layoutSubtreeIfNeeded()
                        window.contentView?.displayIfNeeded()
                    }
                    for paneId in tab.bonsplitController.allPaneIds {
                        guard let selected = tab.bonsplitController.selectedTab(inPane: paneId),
                              let terminal = tab.panel(for: selected.id) as? TerminalPanel else {
                            continue
                        }
                        terminal.hostedView.reconcileGeometryNow()
                        terminal.surface.forceRefresh()
                    }
                }

                var finalState = collectSplitCloseRightState()
                for attempt in 1...8 {
                    reconcileVisibleTerminalGeometry()
                    await Task.yield()
                    finalState = collectSplitCloseRightState()
                    var payload = finalState.data
                    payload["finalAttempt"] = String(attempt)
                    self.writeSplitCloseRightTestData(payload, at: path)
                    if finalState.settled {
                        break
                    }
                }
            }
        }
    }

	    @MainActor
	    private func runSplitCloseRightVisualRepro(
	        tab: Workspace,
	        topLeftPanelId: UUID,
	        path: String,
	        shotsDir: String,
	        iterations: Int,
	        burstFrames: Int,
	        closeDelayMs: Int,
	        pattern: String
	    ) async {
        _ = shotsDir // legacy: screenshots removed in favor of IOSurface sampling

        func sendText(_ panelId: UUID, _ text: String) {
            guard let tp = tab.terminalPanel(for: panelId) else { return }
            tp.surface.sendText(text)
        }

        // Sample a very top strip so the probe remains valid even after vertical expand/collapse.
        // We pin marker text to row 1 before each close sequence.
        let sampleCrop = CGRect(x: 0.04, y: 0.01, width: 0.92, height: 0.08)

        for i in 1...iterations {
            // Reset to a single pane: close everything except the top-left panel.
            tab.focusPanel(topLeftPanelId)
            let toClose = Array(tab.panels.keys).filter { $0 != topLeftPanelId }
            for pid in toClose {
                tab.closePanel(pid, force: true)
            }

            // Create the repro layout. Most patterns use a 2x2 grid, but keep a single-split
            // variant for the exact "close right in a horizontal pair" user report.
            let topLeftId = topLeftPanelId
            let topRight: TerminalPanel
            var bottomLeft: TerminalPanel?
            var bottomRight: TerminalPanel?

            switch pattern {
            case "close_right_single":
                guard let tr = tab.newTerminalSplit(from: topLeftId, orientation: .horizontal) else {
                    writeSplitCloseRightTestData(["setupError": "Failed to split right from top-left (iteration \(i))"], at: path)
                    return
                }
                topRight = tr
            case "close_right_lrtd", "close_right_lrtd_bottom_first", "close_right_bottom_first", "close_right_lrtd_unfocused":
                // User repro: split left/right first, then split top/down in each column.
                guard let tr = tab.newTerminalSplit(from: topLeftId, orientation: .horizontal) else {
                    writeSplitCloseRightTestData(["setupError": "Failed to split right from top-left (iteration \(i))"], at: path)
                    return
                }
                guard let bl = tab.newTerminalSplit(from: topLeftId, orientation: .vertical) else {
                    writeSplitCloseRightTestData(["setupError": "Failed to split down from left (iteration \(i))"], at: path)
                    return
                }
                guard let br = tab.newTerminalSplit(from: tr.id, orientation: .vertical) else {
                    writeSplitCloseRightTestData(["setupError": "Failed to split down from right (iteration \(i))"], at: path)
                    return
                }
                topRight = tr
                bottomLeft = bl
                bottomRight = br
            default:
                // Default: split top/down first, then split left/right in each row.
                guard let bl = tab.newTerminalSplit(from: topLeftId, orientation: .vertical) else {
                    writeSplitCloseRightTestData(["setupError": "Failed to split down from top-left (iteration \(i))"], at: path)
                    return
                }
                guard let br = tab.newTerminalSplit(from: bl.id, orientation: .horizontal) else {
                    writeSplitCloseRightTestData(["setupError": "Failed to split right from bottom-left (iteration \(i))"], at: path)
                    return
                }
                guard let tr = tab.newTerminalSplit(from: topLeftId, orientation: .horizontal) else {
                    writeSplitCloseRightTestData(["setupError": "Failed to split right from top-left (iteration \(i))"], at: path)
                    return
                }
                topRight = tr
                bottomLeft = bl
                bottomRight = br
            }

            // Let newly created surfaces attach before priming content, so sampled panes have
            // stable non-blank text before the close timeline begins.
            try? await Task.sleep(nanoseconds: 180_000_000)

            // Fill left panes with visible content.
            sendText(topLeftId, "printf '\\033[2J\\033[H'; for i in {1..200}; do echo CMUX_SPLIT_TOPLEFT_\(i); done; printf '\\033[HCMUX_MARKER_TOPLEFT\\n'\r")
            sendText(topRight.id, "printf '\\033[2J\\033[H'; for i in {1..200}; do echo CMUX_SPLIT_TOPRIGHT_\(i); done; printf '\\033[HCMUX_MARKER_TOPRIGHT\\n'\r")
            if let bottomLeft {
                sendText(bottomLeft.id, "printf '\\033[2J\\033[H'; for i in {1..200}; do echo CMUX_SPLIT_BOTTOMLEFT_\(i); done; printf '\\033[HCMUX_MARKER_BOTTOMLEFT\\n'\r")
            }
            if let bottomRight {
                sendText(bottomRight.id, "printf '\\033[2J\\033[H'; for i in {1..200}; do echo CMUX_SPLIT_BOTTOMRIGHT_\(i); done; printf '\\033[HCMUX_MARKER_BOTTOMRIGHT\\n'\r")
            }
            // Give shell output a moment to paint before we start the close timeline.
            try? await Task.sleep(nanoseconds: 180_000_000)

            let desiredFrames = max(16, min(burstFrames, 60))
            let closeFrame = min(6, max(1, desiredFrames / 4))
            let delayFrames = max(0, Int((Double(max(0, closeDelayMs)) / 16.6667).rounded(.up)))
            let secondCloseFrame = min(desiredFrames - 1, closeFrame + delayFrames)

            var closeOrder = ""
            let actions: [(frame: Int, action: () -> Void)] = {
                switch pattern {
                case "close_right_single":
                    closeOrder = "TR_ONLY"
                    return [
                        (frame: closeFrame, action: {
                            tab.focusPanel(topRight.id)
                            tab.closePanel(topRight.id, force: true)
                        }),
                    ]
                case "close_bottom":
                    guard let bottomRight, let bottomLeft else { return [] }
                    closeOrder = "BR_THEN_BL"
                    return [
                        (frame: closeFrame, action: {
                            tab.focusPanel(bottomRight.id)
                            tab.closePanel(bottomRight.id, force: true)
                        }),
                        (frame: secondCloseFrame, action: {
                            tab.focusPanel(bottomLeft.id)
                            tab.closePanel(bottomLeft.id, force: true)
                        }),
                    ]
                case "close_right_lrtd_bottom_first", "close_right_bottom_first":
                    guard let bottomRight else { return [] }
                    closeOrder = "BR_THEN_TR"
                    return [
                        (frame: closeFrame, action: {
                            tab.focusPanel(bottomRight.id)
                            tab.closePanel(bottomRight.id, force: true)
                        }),
                        (frame: secondCloseFrame, action: {
                            tab.focusPanel(topRight.id)
                            tab.closePanel(topRight.id, force: true)
                        }),
                    ]
                case "close_right_lrtd_unfocused":
                    guard let bottomRight else { return [] }
                    closeOrder = "TR_THEN_BR_UNFOCUSED"
                    return [
                        (frame: closeFrame, action: {
                            tab.closePanel(topRight.id, force: true)
                        }),
                        (frame: secondCloseFrame, action: {
                            tab.closePanel(bottomRight.id, force: true)
                        }),
                    ]
                default:
                    guard let bottomRight else { return [] }
                    closeOrder = "TR_THEN_BR"
                    return [
                        (frame: closeFrame, action: {
                            tab.focusPanel(topRight.id)
                            tab.closePanel(topRight.id, force: true)
                        }),
                        (frame: secondCloseFrame, action: {
                            tab.focusPanel(bottomRight.id)
                            tab.closePanel(bottomRight.id, force: true)
                        }),
                    ]
                }
            }()

            let targets: [(label: String, view: GhosttySurfaceScrollView)] = {
                switch pattern {
                case "close_right_single":
                    return [
                        ("TL", tab.terminalPanel(for: topLeftId)!.surface.hostedView),
                    ]
                case "close_bottom":
                    return [
                        ("TL", tab.terminalPanel(for: topLeftId)!.surface.hostedView),
                        ("TR", topRight.surface.hostedView),
                    ]
                case "close_right_lrtd_bottom_first", "close_right_bottom_first":
                    return [
                        ("TR", topRight.surface.hostedView),
                        ("TL", tab.terminalPanel(for: topLeftId)!.surface.hostedView),
                    ]
                default:
                    guard let bottomLeft else { return [] }
                    return [
                        ("TL", tab.terminalPanel(for: topLeftId)!.surface.hostedView),
                        ("BL", bottomLeft.surface.hostedView),
                    ]
                }
            }()

            let result = await captureVsyncIOSurfaceTimeline(
                frameCount: desiredFrames,
                closeFrame: closeFrame,
                crop: sampleCrop,
                targets: targets,
                actions: actions
            )

            let paneStateTrace: String = {
                tab.bonsplitController.allPaneIds.map { paneId in
                    let tabs = tab.bonsplitController.tabs(inPane: paneId)
                    let selected = tab.bonsplitController.selectedTab(inPane: paneId)
                    let selectedId = selected.map { String(describing: $0.id) } ?? "nil"
                    let selectedPanelId = selected.flatMap { tab.panelIdFromSurfaceId($0.id) }
                    let selectedPanelLive: String = {
                        guard let selected else { return "0" }
                        return tab.panel(for: selected.id) != nil ? "1" : "0"
                    }()
                    let mappedCount = tabs.filter { tab.panelIdFromSurfaceId($0.id) != nil }.count
                    let selectedPanel = selectedPanelId?.uuidString.prefix(8) ?? "nil"
                    return "pane=\(paneId.id.uuidString.prefix(8)):tabs=\(tabs.count):mapped=\(mappedCount):selected=\(selectedId.prefix(8)):selectedPanel=\(selectedPanel):selectedLive=\(selectedPanelLive)"
                }.joined(separator: ";")
            }()

            writeSplitCloseRightTestData([
                "pattern": pattern,
                "iteration": String(i),
                "closeDelayMs": String(closeDelayMs),
                "closeDelayFrames": String(delayFrames),
                "closeOrder": closeOrder,
                "timelineFrameCount": String(desiredFrames),
                "timelineCloseFrame": String(closeFrame),
                "timelineSecondCloseFrame": String(secondCloseFrame),
                "timelineFirstBlank": result.firstBlank.map { "\($0.label)@\($0.frame)" } ?? "",
                "timelineFirstSizeMismatch": result.firstSizeMismatch.map { "\($0.label)@\($0.frame):ios=\($0.ios):exp=\($0.expected)" } ?? "",
                "timelineTrace": result.trace.joined(separator: "|"),
                "timelinePaneState": paneStateTrace,
                "visualLastIteration": String(i),
            ], at: path)

            if let firstBlank = result.firstBlank {
                writeSplitCloseRightTestData([
                    "blankFrameSeen": "1",
                    "blankObservedIteration": String(i),
                    "blankObservedAt": "\(firstBlank.label)@\(firstBlank.frame)"
                ], at: path)
                return
            }

            if let firstMismatch = result.firstSizeMismatch {
                writeSplitCloseRightTestData([
                    "sizeMismatchSeen": "1",
                    "sizeMismatchObservedIteration": String(i),
                    "sizeMismatchObservedAt": "\(firstMismatch.label)@\(firstMismatch.frame):ios=\(firstMismatch.ios):exp=\(firstMismatch.expected)"
                ], at: path)
                return
            }
        }
	    }

	    @MainActor
	    private func captureVsyncIOSurfaceTimeline(
	        frameCount: Int,
	        closeFrame: Int,
	        crop: CGRect,
	        targets: [(label: String, view: GhosttySurfaceScrollView)],
	        actions: [(frame: Int, action: () -> Void)] = []
	    ) async -> (firstBlank: (label: String, frame: Int)?, firstSizeMismatch: (label: String, frame: Int, ios: String, expected: String)?, trace: [String]) {
	        guard frameCount > 0 else { return (nil, nil, []) }

	        let st = VsyncIOSurfaceTimelineState(frameCount: frameCount, closeFrame: closeFrame)
	        st.scheduledActions = actions.sorted(by: { $0.frame < $1.frame })
	        st.nextActionIndex = 0
	        st.targets = targets.map { t in
	            VsyncIOSurfaceTimelineState.Target(label: t.label, sample: { @MainActor in
	                t.view.debugSampleIOSurface(normalizedCrop: crop)
	            })
	        }

	        let unmanaged = Unmanaged.passRetained(st)
	        let ctx = unmanaged.toOpaque()

	        await withCheckedContinuation { (cont: CheckedContinuation<Void, Never>) in
	            st.continuation = cont
	            var link: CVDisplayLink?
	            CVDisplayLinkCreateWithActiveCGDisplays(&link)
	            guard let link else {
	                st.finish()
	                Unmanaged<VsyncIOSurfaceTimelineState>.fromOpaque(ctx).release()
	                return
	            }
	            st.link = link

	            CVDisplayLinkSetOutputCallback(link, cmuxVsyncIOSurfaceTimelineCallback, ctx)
	            CVDisplayLinkStart(link)
	        }

	        return (st.firstBlank, st.firstSizeMismatch, st.trace)
	    }

    private func writeSplitCloseRightTestData(_ updates: [String: String], at path: String) {
        var payload = loadSplitCloseRightTestData(at: path)
        for (key, value) in updates {
            payload[key] = value
        }
        guard let data = try? JSONSerialization.data(withJSONObject: payload) else { return }
        try? data.write(to: URL(fileURLWithPath: path), options: .atomic)
    }

    private func loadSplitCloseRightTestData(at path: String) -> [String: String] {
        guard let data = try? Data(contentsOf: URL(fileURLWithPath: path)),
              let object = try? JSONSerialization.jsonObject(with: data) as? [String: String] else {
            return [:]
        }
        return object
    }

    private func setupChildExitSplitUITestIfNeeded() {
        guard !didSetupChildExitSplitUITest else { return }
        didSetupChildExitSplitUITest = true

        let env = ProcessInfo.processInfo.environment
        guard env["CMUX_UI_TEST_CHILD_EXIT_SPLIT_SETUP"] == "1" else { return }
        guard let path = env["CMUX_UI_TEST_CHILD_EXIT_SPLIT_PATH"], !path.isEmpty else { return }
        let requestedIterations = Int(env["CMUX_UI_TEST_CHILD_EXIT_SPLIT_ITERATIONS"] ?? "1") ?? 1
        let iterations = max(1, min(requestedIterations, 20))

        func write(_ updates: [String: String]) {
            var payload: [String: String] = {
                guard let data = try? Data(contentsOf: URL(fileURLWithPath: path)),
                      let obj = try? JSONSerialization.jsonObject(with: data) as? [String: String] else {
                    return [:]
                }
                return obj
            }()
            for (k, v) in updates { payload[k] = v }
            guard let out = try? JSONSerialization.data(withJSONObject: payload) else { return }
            try? out.write(to: URL(fileURLWithPath: path), options: .atomic)
        }

        Task { @MainActor [weak self] in
            guard let self else { return }
            // Small delay so the initial window/panel has completed first layout.
            try? await Task.sleep(nanoseconds: 200_000_000)

            guard let tab = self.selectedWorkspace else {
                write(["setupError": "Missing selected workspace", "done": "1"])
                return
            }
            write([
                "requestedIterations": String(requestedIterations),
                "iterations": String(iterations),
                "workspaceCountBefore": String(self.tabs.count),
                "panelCountBefore": String(tab.panels.count),
                "done": "0",
            ])

            var completedIterations = 0
            var timedOut = false
            var closedWorkspace = false

            for i in 1...iterations {
                guard self.tabs.contains(where: { $0.id == tab.id }) else {
                    closedWorkspace = true
                    break
                }

                guard let leftPanelId = tab.focusedPanelId ?? tab.panels.keys.first else {
                    write(["setupError": "Missing focused panel before iteration \(i)", "done": "1"])
                    return
                }

                // Start each iteration from a deterministic 1x1 workspace.
                if tab.panels.count > 1 {
                    for panelId in tab.panels.keys where panelId != leftPanelId {
                        tab.closePanel(panelId, force: true)
                    }
                    let collapsed = await self.waitForWorkspacePanelsCondition(
                        tab: tab,
                        timeoutSeconds: 2.0
                    ) { workspace in
                        workspace.panels.count == 1
                    }
                    if !collapsed {
                        write(["setupError": "Timed out collapsing workspace before iteration \(i)", "done": "1"])
                        return
                    }
                }

                guard let rightPanel = tab.newTerminalSplit(from: leftPanelId, orientation: .horizontal) else {
                    write(["setupError": "Failed to create right split at iteration \(i)", "done": "1"])
                    return
                }

                write([
                    "iteration": String(i),
                    "leftPanelId": leftPanelId.uuidString,
                    "rightPanelId": rightPanel.id.uuidString,
                ])

                tab.focusPanel(rightPanel.id)
                // Wait for the split terminal surface to be attached before sending exit.
                // Without this, very early writes can be dropped during initial surface creation.
                _ = await self.waitForTerminalPanelCondition(
                    tab: tab,
                    panelId: rightPanel.id,
                    timeoutSeconds: 2.0
                ) { panel in
                    panel.hostedView.window != nil && panel.surface.surface != nil
                }
                // Use an explicit shell exit command for deterministic child-exit behavior across
                // startup timing variance; this still exercises the same SHOW_CHILD_EXITED path.
                rightPanel.surface.sendText("exit\r")

                // Wait for the right panel to close.
                let closed = await withCheckedContinuation { (cont: CheckedContinuation<Bool, Never>) in
                    var cancellable: AnyCancellable?
                    var resolved = false

                    func finish(_ value: Bool) {
                        guard !resolved else { return }
                        resolved = true
                        cancellable?.cancel()
                        cont.resume(returning: value)
                    }

                    cancellable = tab.$panels
                        .map { $0.count }
                        .removeDuplicates()
                        .sink { count in
                            if count == 1 {
                                finish(true)
                            }
                        }

                    DispatchQueue.main.asyncAfter(deadline: .now() + 8.0) {
                        finish(false)
                    }
                }

                if !closed {
                    timedOut = true
                    write(["timedOutIteration": String(i)])
                    break
                }

                if !self.tabs.contains(where: { $0.id == tab.id }) {
                    closedWorkspace = true
                    write(["closedWorkspaceIteration": String(i)])
                    break
                }

                completedIterations = i
            }

            let workspaceStillOpen = self.tabs.contains(where: { $0.id == tab.id })
            let effectiveClosedWorkspace = closedWorkspace || !workspaceStillOpen

            write([
                "workspaceCountAfter": String(self.tabs.count),
                "panelCountAfter": String(tab.panels.count),
                "workspaceStillOpen": workspaceStillOpen ? "1" : "0",
                "closedWorkspace": effectiveClosedWorkspace ? "1" : "0",
                "timedOut": timedOut ? "1" : "0",
                "completedIterations": String(completedIterations),
                "done": "1",
            ])
        }
    }

    private func setupChildExitKeyboardUITestIfNeeded() {
        guard !didSetupChildExitKeyboardUITest else { return }
        didSetupChildExitKeyboardUITest = true

        let env = ProcessInfo.processInfo.environment
        guard env["CMUX_UI_TEST_CHILD_EXIT_KEYBOARD_SETUP"] == "1" else { return }
        guard let path = env["CMUX_UI_TEST_CHILD_EXIT_KEYBOARD_PATH"], !path.isEmpty else { return }
        let autoTrigger = env["CMUX_UI_TEST_CHILD_EXIT_KEYBOARD_AUTO_TRIGGER"] == "1"
        let strictKeyOnly = env["CMUX_UI_TEST_CHILD_EXIT_KEYBOARD_STRICT"] == "1"
        let triggerMode = (env["CMUX_UI_TEST_CHILD_EXIT_KEYBOARD_TRIGGER_MODE"] ?? "shell_input")
            .trimmingCharacters(in: .whitespacesAndNewlines)
        let useEarlyCtrlShiftTrigger = triggerMode == "early_ctrl_shift_d"
        let useEarlyCtrlDTrigger = triggerMode == "early_ctrl_d"
        let useEarlyTrigger = useEarlyCtrlShiftTrigger || useEarlyCtrlDTrigger
        let triggerUsesShift = triggerMode == "ctrl_shift_d" || useEarlyCtrlShiftTrigger
        let layout = (env["CMUX_UI_TEST_CHILD_EXIT_KEYBOARD_LAYOUT"] ?? "lr")
            .trimmingCharacters(in: .whitespacesAndNewlines)
        let expectedPanelsAfter = max(
            1,
            Int((env["CMUX_UI_TEST_CHILD_EXIT_KEYBOARD_EXPECTED_PANELS_AFTER"] ?? "1")
                .trimmingCharacters(in: .whitespacesAndNewlines)
            ) ?? 1
        )

        func write(_ updates: [String: String]) {
            var payload: [String: String] = {
                guard let data = try? Data(contentsOf: URL(fileURLWithPath: path)),
                      let obj = try? JSONSerialization.jsonObject(with: data) as? [String: String] else {
                    return [:]
                }
                return obj
            }()
            for (k, v) in updates { payload[k] = v }
            guard let out = try? JSONSerialization.data(withJSONObject: payload) else { return }
            try? out.write(to: URL(fileURLWithPath: path), options: .atomic)
        }

        Task { @MainActor [weak self] in
            guard let self else { return }
            try? await Task.sleep(nanoseconds: 200_000_000)

            guard let tab = self.selectedWorkspace else {
                write(["setupError": "Missing selected workspace", "done": "1"])
                return
            }
            guard let leftPanelId = tab.focusedPanelId else {
                write(["setupError": "Missing initial focused panel", "done": "1"])
                return
            }
            guard let rightPanel = tab.newTerminalSplit(from: leftPanelId, orientation: .horizontal) else {
                write(["setupError": "Failed to create right split", "done": "1"])
                return
            }

            var bottomLeftPanelId = ""
            let topRightPanelId = rightPanel.id.uuidString
            var bottomRightPanelId = ""
            var exitPanelId = rightPanel.id

            if layout == "lr_left_vertical" {
                guard let bottomLeft = tab.newTerminalSplit(from: leftPanelId, orientation: .vertical) else {
                    write(["setupError": "Failed to create bottom-left split", "done": "1"])
                    return
                }
                bottomLeftPanelId = bottomLeft.id.uuidString
            } else if layout == "lrtd_close_right_then_exit_top_left" {
                guard let bottomLeft = tab.newTerminalSplit(from: leftPanelId, orientation: .vertical) else {
                    write(["setupError": "Failed to create bottom-left split", "done": "1"])
                    return
                }
                guard let bottomRight = tab.newTerminalSplit(from: rightPanel.id, orientation: .vertical) else {
                    write(["setupError": "Failed to create bottom-right split", "done": "1"])
                    return
                }
                bottomLeftPanelId = bottomLeft.id.uuidString
                bottomRightPanelId = bottomRight.id.uuidString

                // Repro flow: with a 2x2 (left/right then top/down), close both right panes,
                // then trigger Ctrl+D in top-left.
                tab.focusPanel(rightPanel.id)
                tab.closePanel(rightPanel.id, force: true)
                tab.focusPanel(bottomRight.id)
                tab.closePanel(bottomRight.id, force: true)
                exitPanelId = leftPanelId

                let collapsed = await self.waitForWorkspacePanelsCondition(
                    tab: tab,
                    timeoutSeconds: 2.0
                ) { workspace in
                    workspace.panels.count == 2
                }
                if !collapsed {
                    write([
                        "setupError": "Expected 2 panels after closing right column, got \(tab.panels.count)",
                        "done": "1",
                    ])
                    return
                }
            } else if layout == "tdlr_close_bottom_then_exit_top_left" {
                // Alternate repro flow:
                // 1) split top/down
                // 2) split left/right for each row (2x2)
                // 3) close both bottom panes
                // 4) trigger Ctrl+D in top-left
                guard let bottomLeft = tab.newTerminalSplit(from: leftPanelId, orientation: .vertical) else {
                    write(["setupError": "Failed to create bottom-left split", "done": "1"])
                    return
                }
                guard let topRight = tab.newTerminalSplit(from: leftPanelId, orientation: .horizontal) else {
                    write(["setupError": "Failed to create top-right split", "done": "1"])
                    return
                }
                guard let bottomRight = tab.newTerminalSplit(from: bottomLeft.id, orientation: .horizontal) else {
                    write(["setupError": "Failed to create bottom-right split", "done": "1"])
                    return
                }
                bottomLeftPanelId = bottomLeft.id.uuidString
                bottomRightPanelId = bottomRight.id.uuidString

                // Close every pane except the top row; do it one-by-one and wait for model convergence.
                let keepPanels: Set<UUID> = [leftPanelId, topRight.id]
                for panelId in Array(tab.panels.keys) where !keepPanels.contains(panelId) {
                    tab.focusPanel(panelId)
                    tab.closePanel(panelId, force: true)
                    let closed = await self.waitForWorkspacePanelsCondition(
                        tab: tab,
                        timeoutSeconds: 1.0
                    ) { workspace in
                        workspace.panels[panelId] == nil
                    }
                    if !closed {
                        write([
                            "setupError": "Failed to close bottom pane \(panelId.uuidString)",
                            "done": "1",
                        ])
                        return
                    }
                }
                exitPanelId = leftPanelId

                let collapsed = await self.waitForWorkspacePanelsCondition(
                    tab: tab,
                    timeoutSeconds: 2.0
                ) { workspace in
                    workspace.panels.count == 2
                }
                if !collapsed {
                    write([
                        "setupError": "Expected 2 panels after closing bottom row, got \(tab.panels.count)",
                        "done": "1",
                    ])
                    return
                }
            }

            tab.focusPanel(exitPanelId)
            // Keep child-exit keyboard tests deterministic across user shell configs.
            // `exec cat` exits on a single Ctrl+D and avoids ignore-eof shell settings.
            if let exitPanel = tab.terminalPanel(for: exitPanelId) {
                exitPanel.sendText("exec cat\r")
            }

            var exitPanelAttachedBeforeCtrlD = false
            var exitPanelHasSurfaceBeforeCtrlD = false
            if !useEarlyTrigger {
                let readiness = await self.waitForTerminalPanelReadyForUITest(
                    tab: tab,
                    panelId: exitPanelId
                )
                exitPanelAttachedBeforeCtrlD = readiness.attached
                exitPanelHasSurfaceBeforeCtrlD = readiness.hasSurface
                if !(readiness.attached && readiness.hasSurface) {
                    write([
                        "exitPanelAttachedBeforeCtrlD": readiness.attached ? "1" : "0",
                        "exitPanelHasSurfaceBeforeCtrlD": readiness.hasSurface ? "1" : "0",
                        "setupError": "Exit panel not ready for Ctrl+D (not attached or surface nil)",
                        "done": "1",
                    ])
                    return
                }
                self.ensureFocusedTerminalFirstResponder()
            } else if let exitPanel = tab.terminalPanel(for: exitPanelId) {
                exitPanelAttachedBeforeCtrlD = exitPanel.hostedView.window != nil
                exitPanelHasSurfaceBeforeCtrlD = exitPanel.surface.surface != nil
            }

            let focusedPanelBefore = tab.focusedPanelId?.uuidString ?? ""
            let firstResponderPanelBefore = tab.panels.compactMap { (panelId, panel) -> UUID? in
                guard let terminal = panel as? TerminalPanel else { return nil }
                return terminal.hostedView.isSurfaceViewFirstResponder() ? panelId : nil
            }.first?.uuidString ?? ""

            write([
                "workspaceId": tab.id.uuidString,
                "leftPanelId": leftPanelId.uuidString,
                "rightPanelId": rightPanel.id.uuidString,
                "topRightPanelId": topRightPanelId,
                "bottomLeftPanelId": bottomLeftPanelId,
                "bottomRightPanelId": bottomRightPanelId,
                "exitPanelId": exitPanelId.uuidString,
                "panelCountBeforeCtrlD": String(tab.panels.count),
                "layout": layout,
                "expectedPanelsAfter": String(expectedPanelsAfter),
                "focusedPanelBefore": focusedPanelBefore,
                "firstResponderPanelBefore": firstResponderPanelBefore,
                "exitPanelAttachedBeforeCtrlD": exitPanelAttachedBeforeCtrlD ? "1" : "0",
                "exitPanelHasSurfaceBeforeCtrlD": exitPanelHasSurfaceBeforeCtrlD ? "1" : "0",
                "ready": "1",
                "done": "0",
            ])

            var finished = false
            var timeoutWork: DispatchWorkItem?

            @MainActor
            func finish(_ updates: [String: String]) {
                guard !finished else { return }
                finished = true
                timeoutWork?.cancel()
                write(updates.merging(["done": "1"], uniquingKeysWith: { _, new in new }))
                self.uiTestCancellables.removeAll()
            }

            tab.$panels
                .map { $0.count }
                .removeDuplicates()
                .sink { [weak self, weak tab] count in
                    Task { @MainActor in
                        guard let self, let tab else { return }
                        if count == expectedPanelsAfter {
                            // Require the post-exit state to be stable for a short window so
                            // we catch "close looked correct, then workspace vanished" races.
                            try? await Task.sleep(nanoseconds: 1_200_000_000)
                            guard tab.panels.count == expectedPanelsAfter else { return }

                            let firstResponderPanelAfter = tab.panels.compactMap { (panelId, panel) -> UUID? in
                                guard let terminal = panel as? TerminalPanel else { return nil }
                                return terminal.hostedView.isSurfaceViewFirstResponder() ? panelId : nil
                            }.first?.uuidString ?? ""

                            finish([
                                "workspaceCountAfter": String(self.tabs.count),
                                "panelCountAfter": String(tab.panels.count),
                                "closedWorkspace": self.tabs.contains(where: { $0.id == tab.id }) ? "0" : "1",
                                "focusedPanelAfter": tab.focusedPanelId?.uuidString ?? "",
                                "firstResponderPanelAfter": firstResponderPanelAfter,
                            ])
                        }
                    }
                }
                .store(in: &uiTestCancellables)

            $tabs
                .map { $0.contains(where: { $0.id == tab.id }) }
                .removeDuplicates()
                .sink { alive in
                    Task { @MainActor in
                        if !alive {
                            finish([
                                "workspaceCountAfter": "0",
                                "panelCountAfter": "0",
                                "closedWorkspace": "1",
                            ])
                        }
                    }
                }
                .store(in: &uiTestCancellables)

            let work = DispatchWorkItem {
                finish([
                    "workspaceCountAfter": String(self.tabs.count),
                    "panelCountAfter": String(tab.panels.count),
                    "closedWorkspace": self.tabs.contains(where: { $0.id == tab.id }) ? "0" : "1",
                    "timedOut": "1",
                ])
            }
            timeoutWork = work
            DispatchQueue.main.asyncAfter(deadline: .now() + 8.0, execute: work)

            if autoTrigger {
                Task { @MainActor [weak tab] in
                    guard let tab else { return }
                    write(["autoTriggerStarted": "1"])

                    if triggerMode == "runtime_close_callback" {
                        write(["autoTriggerMode": "runtime_close_callback"])
                        self.closePanelAfterChildExited(tabId: tab.id, surfaceId: exitPanelId)
                        return
                    }

                    let triggerModifiers: NSEvent.ModifierFlags = triggerUsesShift
                        ? [.control, .shift]
                        : [.control]
                    let shouldWaitForSurface = !useEarlyTrigger

                    var attachedBeforeTrigger = false
                    var hasSurfaceBeforeTrigger = false
                    if shouldWaitForSurface {
                        let ready = await self.waitForTerminalPanelCondition(
                            tab: tab,
                            panelId: exitPanelId,
                            timeoutSeconds: 5.0
                        ) { panel in
                            attachedBeforeTrigger = panel.hostedView.window != nil
                            hasSurfaceBeforeTrigger = panel.surface.surface != nil
                            return attachedBeforeTrigger && hasSurfaceBeforeTrigger
                        }
                        if !ready,
                           tab.terminalPanel(for: exitPanelId) == nil {
                            write(["autoTriggerError": "missingExitPanelBeforeTrigger"])
                            return
                        }
                    } else if let panel = tab.terminalPanel(for: exitPanelId) {
                        attachedBeforeTrigger = panel.hostedView.window != nil
                        hasSurfaceBeforeTrigger = panel.surface.surface != nil
                    }
                    write([
                        "exitPanelAttachedBeforeTrigger": attachedBeforeTrigger ? "1" : "0",
                        "exitPanelHasSurfaceBeforeTrigger": hasSurfaceBeforeTrigger ? "1" : "0",
                    ])
                    if shouldWaitForSurface && !(attachedBeforeTrigger && hasSurfaceBeforeTrigger) {
                        write(["autoTriggerError": "exitPanelNotReadyBeforeTrigger"])
                        return
                    }

                    guard let panel = tab.terminalPanel(for: exitPanelId) else {
                        write(["autoTriggerError": "missingExitPanelAtTrigger"])
                        return
                    }
                    // Exercise the real key path (ghostty_surface_key for Ctrl+D).
                    if panel.hostedView.sendSyntheticCtrlDForUITest(modifierFlags: triggerModifiers) {
                        write(["autoTriggerSentCtrlDKey1": "1"])
                    } else {
                        write([
                            "autoTriggerCtrlDKeyUnavailable": "1",
                            "autoTriggerError": "ctrlDKeyUnavailable",
                        ])
                        return
                    }

                    // In strict mode, never mask routing bugs with fallback writes.
                    if strictKeyOnly {
                        let strictModeLabel: String = {
                            if useEarlyCtrlShiftTrigger { return "strict_early_ctrl_shift_d" }
                            if useEarlyCtrlDTrigger { return "strict_early_ctrl_d" }
                            if triggerUsesShift { return "strict_ctrl_shift_d" }
                            return "strict_ctrl_d"
                        }()
                        write(["autoTriggerMode": strictModeLabel])
                        return
                    }

                    // Non-strict mode keeps one additional Ctrl+D retry for startup timing variance.
                    try? await Task.sleep(nanoseconds: 450_000_000)
                    if tab.panels[exitPanelId] != nil,
                       panel.hostedView.sendSyntheticCtrlDForUITest(modifierFlags: triggerModifiers) {
                        write(["autoTriggerSentCtrlDKey2": "1"])
                    }
                }
            }
        }
    }
#endif
}

extension TabManager {
    func sessionAutosaveFingerprint() -> Int {
        var hasher = Hasher()
        hasher.combine(selectedTabId)
        hasher.combine(tabs.count)

        for workspace in tabs.prefix(SessionPersistencePolicy.maxWorkspacesPerWindow) {
            hasher.combine(workspace.id)
            hasher.combine(workspace.focusedPanelId)
            hasher.combine(workspace.currentDirectory)
            hasher.combine(workspace.customTitle ?? "")
            hasher.combine(workspace.customColor ?? "")
            hasher.combine(workspace.isPinned)
            hasher.combine(workspace.panels.count)
            hasher.combine(workspace.statusEntries.count)
            hasher.combine(workspace.metadataBlocks.count)
            hasher.combine(workspace.logEntries.count)
            hasher.combine(workspace.panelDirectories.count)
            hasher.combine(workspace.panelTitles.count)
            hasher.combine(workspace.panelPullRequests.count)
            hasher.combine(workspace.panelGitBranches.count)
            hasher.combine(workspace.surfaceListeningPorts.count)

            if let progress = workspace.progress {
                hasher.combine(Int((progress.value * 1000).rounded()))
                hasher.combine(progress.label)
            } else {
                hasher.combine(-1)
            }

            if let gitBranch = workspace.gitBranch {
                hasher.combine(gitBranch.branch)
                hasher.combine(gitBranch.isDirty)
            } else {
                hasher.combine("")
                hasher.combine(false)
            }
        }

        return hasher.finalize()
    }

    func sessionSnapshot(includeScrollback: Bool) -> SessionTabManagerSnapshot {
        let restorableTabs = tabs
            .filter { !$0.isRemoteWorkspace }
            .prefix(SessionPersistencePolicy.maxWorkspacesPerWindow)
        let workspaceSnapshots = restorableTabs
            .map { $0.sessionSnapshot(includeScrollback: includeScrollback) }
        let selectedWorkspaceIndex = selectedTabId.flatMap { selectedTabId in
            restorableTabs.firstIndex(where: { $0.id == selectedTabId })
        }
        return SessionTabManagerSnapshot(
            selectedWorkspaceIndex: selectedWorkspaceIndex,
            workspaces: workspaceSnapshots
        )
    }

    private func releaseRestoredAwayWorkspace(_ workspace: Workspace) {
        // Session restore replaces the bootstrap workspace objects with freshly
        // restored ones. Tear the old graph down after the atomic swap so late
        // panel/socket callbacks cannot keep mutating hidden pre-restore state.
        AppDelegate.shared?.notificationStore?.clearNotifications(forTabId: workspace.id)
        workspace.teardownAllPanels()
        workspace.teardownRemoteConnection()
        workspace.owningTabManager = nil
    }

    func restoreSessionSnapshot(_ snapshot: SessionTabManagerSnapshot) {
        let previousTabs = tabs
        for tab in previousTabs {
            unwireClosedBrowserTracking(for: tab)
        }
        let existingProbeKeys = Set(workspaceGitProbeGenerationByKey.keys)
            .union(workspaceGitProbeTimersByKey.keys)
        for key in existingProbeKeys {
            clearWorkspaceGitProbe(key)
        }

        // Clear non-@Published state without touching tabs/selectedTabId yet.
        lastFocusedPanelByTab.removeAll()
        pendingPanelTitleUpdates.removeAll()
        tabHistory.removeAll()
        historyIndex = -1
        isNavigatingHistory = false
        pendingWorkspaceUnfocusTarget = nil
        workspaceCycleCooldownTask?.cancel()
        workspaceCycleCooldownTask = nil
        isWorkspaceCycleHot = false
        selectionSideEffectsGeneration &+= 1
        recentlyClosedBrowsers = RecentlyClosedBrowserStack(capacity: 20)

        // Build the new workspace list locally to avoid intermediate @Published
        // emissions (empty tabs, nil selectedTabId) that can leave SwiftUI's
        // mountedWorkspaceIds empty and cause a frozen blank launch state (#399).
        var newTabs: [Workspace] = []
        let workspaceSnapshots = snapshot.workspaces
            .prefix(SessionPersistencePolicy.maxWorkspacesPerWindow)
        for workspaceSnapshot in workspaceSnapshots {
            let ordinal = Self.nextPortOrdinal
            Self.nextPortOrdinal += 1
            let workspace = Workspace(
                title: workspaceSnapshot.processTitle,
                workingDirectory: workspaceSnapshot.currentDirectory,
                portOrdinal: ordinal
            )
            workspace.owningTabManager = self
            workspace.restoreSessionSnapshot(workspaceSnapshot)
            wireClosedBrowserTracking(for: workspace)
            newTabs.append(workspace)
        }

        if newTabs.isEmpty {
            let ordinal = Self.nextPortOrdinal
            Self.nextPortOrdinal += 1
            let fallback = Workspace(title: "Terminal 1", portOrdinal: ordinal)
            fallback.owningTabManager = self
            wireClosedBrowserTracking(for: fallback)
            newTabs.append(fallback)
        }

        // Determine selection before mutating @Published properties.
        let newSelectedId: UUID?
        if let selectedWorkspaceIndex = snapshot.selectedWorkspaceIndex,
           newTabs.indices.contains(selectedWorkspaceIndex) {
            newSelectedId = newTabs[selectedWorkspaceIndex].id
        } else {
            newSelectedId = newTabs.first?.id
        }

        // Single atomic assignment of @Published properties so SwiftUI observers
        // never see an intermediate state with empty tabs or nil selection.
        tabs = newTabs
        selectedTabId = newSelectedId
        let existingIds = Set(newTabs.map(\.id))
        pruneBackgroundWorkspaceLoads(existingIds: existingIds)
        sidebarSelectedWorkspaceIds.formIntersection(existingIds)
        for workspace in previousTabs {
            releaseRestoredAwayWorkspace(workspace)
        }
        for workspace in newTabs {
            let terminalPanels = workspace.panels.values.compactMap { $0 as? TerminalPanel }
            for terminalPanel in terminalPanels {
                guard let directory = gitProbeDirectory(for: workspace, panelId: terminalPanel.id) else {
                    continue
                }
                scheduleInitialWorkspaceGitMetadataRefresh(
                    workspaceId: workspace.id,
                    panelId: terminalPanel.id,
                    directory: directory
                )
            }
        }

        if let selectedTabId {
            NotificationCenter.default.post(
                name: .ghosttyDidFocusTab,
                object: nil,
                userInfo: [GhosttyNotificationKey.tabId: selectedTabId]
            )
        }
    }
}

// MARK: - Direction Types for Backwards Compatibility

/// Split direction for backwards compatibility with old API
enum SplitDirection {
    case left, right, up, down

    var isHorizontal: Bool {
        self == .left || self == .right
    }

    var orientation: SplitOrientation {
        isHorizontal ? .horizontal : .vertical
    }

    /// If true, insert the new pane on the "first" side (left/top).
    /// If false, insert on the "second" side (right/bottom).
    var insertFirst: Bool {
        self == .left || self == .up
    }
}

/// Resize direction for backwards compatibility
enum ResizeDirection {
    case left, right, up, down

    var splitOrientation: String {
        switch self {
        case .left, .right:
            return "horizontal"
        case .up, .down:
            return "vertical"
        }
    }

    /// A split controls the target pane's right/bottom edge when the target is
    /// the first child, and left/top edge when the target is the second child.
    var requiresPaneInFirstChild: Bool {
        switch self {
        case .right, .down:
            return true
        case .left, .up:
            return false
        }
    }

    /// Positive values move the divider toward the second child (right/down).
    var dividerDeltaSign: CGFloat {
        requiresPaneInFirstChild ? 1 : -1
    }
}

extension Notification.Name {
    static let commandPaletteToggleRequested = Notification.Name("cmux.commandPaletteToggleRequested")
    static let commandPaletteRequested = Notification.Name("cmux.commandPaletteRequested")
    static let commandPaletteSwitcherRequested = Notification.Name("cmux.commandPaletteSwitcherRequested")
    static let commandPaletteSubmitRequested = Notification.Name("cmux.commandPaletteSubmitRequested")
    static let commandPaletteDismissRequested = Notification.Name("cmux.commandPaletteDismissRequested")
    static let commandPaletteRenameTabRequested = Notification.Name("cmux.commandPaletteRenameTabRequested")
    static let commandPaletteRenameWorkspaceRequested = Notification.Name("cmux.commandPaletteRenameWorkspaceRequested")
    static let commandPaletteMoveSelection = Notification.Name("cmux.commandPaletteMoveSelection")
    static let commandPaletteRenameInputInteractionRequested = Notification.Name("cmux.commandPaletteRenameInputInteractionRequested")
    static let commandPaletteRenameInputDeleteBackwardRequested = Notification.Name("cmux.commandPaletteRenameInputDeleteBackwardRequested")
    static let feedbackComposerRequested = Notification.Name("cmux.feedbackComposerRequested")
    static let ghosttyDidSetTitle = Notification.Name("ghosttyDidSetTitle")
    static let ghosttyDidFocusTab = Notification.Name("ghosttyDidFocusTab")
    static let ghosttyDidFocusSurface = Notification.Name("ghosttyDidFocusSurface")
    static let ghosttyDidBecomeFirstResponderSurface = Notification.Name("ghosttyDidBecomeFirstResponderSurface")
    static let browserDidBecomeFirstResponderWebView = Notification.Name("browserDidBecomeFirstResponderWebView")
    static let browserFocusAddressBar = Notification.Name("browserFocusAddressBar")
    static let browserMoveOmnibarSelection = Notification.Name("browserMoveOmnibarSelection")
    static let browserDidExitAddressBar = Notification.Name("browserDidExitAddressBar")
    static let browserDidFocusAddressBar = Notification.Name("browserDidFocusAddressBar")
    static let browserDidBlurAddressBar = Notification.Name("browserDidBlurAddressBar")
    static let webViewDidReceiveClick = Notification.Name("webViewDidReceiveClick")
    static let terminalPortalVisibilityDidChange = Notification.Name("cmux.terminalPortalVisibilityDidChange")
    static let browserPortalRegistryDidChange = Notification.Name("cmux.browserPortalRegistryDidChange")
}