Fix Cmd+N nightly crash: avoid local Workspace refs in ARC hotpath (#2204)

* test: reproduce Cmd+N snapshot workspace lifetime race

* fix: retain snapshot workspaces through Cmd+N creation

* fix: repair workspace lifetime regression test

* fix: extract workspace config through self to avoid Xcode 16.x ARC crash

The snapshot approach (c1998e34) navigated workspace → panel → surface
through local variables. Xcode 16.4's -O ARC optimizer aggressively
elides retains on these locals through inlined call chains, causing
use-after-free on every Cmd+N in CI-built nightlies.

Fix: extract preferredWorkingDirectory and inheritedTerminalFontPoints
through self (always retained) BEFORE capturing locals. The snapshot
is now purely value-typed with no Workspace references held in locals.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Sources/TabManager.swift

@@ -1207,17 +1207,23 @@ class TabManager: ObservableObject {
         placementOverride: NewWorkspacePlacement? = nil,
         autoWelcomeIfNeeded: Bool = true
     ) -> Workspace {
+        // Extract Workspace-dependent data through `self` BEFORE capturing locals.
+        // Accessing through `self` is safe because the method retains `self` for its
+        // duration, keeping all Workspace objects reachable via `self.tabs`. Local copies
+        // of Workspace references (like a `selectedWorkspace` local) are vulnerable to
+        // Xcode 16.x's aggressive ARC optimizer eliding retains through inlined call
+        // chains (workspace → panel → surface → C pointer), causing use-after-free.
+        let preferredDir = preferredWorkingDirectoryForNewTab()
+        let inheritedFontPoints = inheritedTerminalFontPointsForNewWorkspace()
+
         let capturedTabs = tabs
         let capturedSelectedTabId = selectedTabId
-        // Keep the pre-creation workspace array alive for the full Cmd+N path. Release ARC
-        // can otherwise drop intermediate retains before we re-read `tabs` for insertion,
-        // which turns mid-creation closes into use-after-free crashes in `swift_retain`.
-        return withExtendedLifetime(capturedTabs) {
-            // Snapshot current published state once so workspace creation doesn't repeatedly
-            // bounce through Combine-backed accessors while we're preparing the new workspace.
-            let snapshot = workspaceCreationSnapshot(
+
+        let snapshot = workspaceCreationSnapshotLite(
             currentTabs: capturedTabs,
-                currentSelectedTabId: capturedSelectedTabId
+            currentSelectedTabId: capturedSelectedTabId,
+            preferredWorkingDirectory: preferredDir,
+            inheritedTerminalFontPoints: inheritedFontPoints
         )
         didCaptureWorkspaceCreationSnapshot()
 #if DEBUG
@@ -1298,7 +1304,6 @@ class TabManager: ObservableObject {
         }
         return newWorkspace
     }
-    }
 
     @MainActor
     private func sendWelcomeWhenReady(to workspace: Workspace) {
@@ -2187,31 +2192,36 @@ class TabManager: ObservableObject {
         terminalPanelForWorkspaceConfigInheritanceSource(workspace: selectedWorkspace)
     }
 
-    private func workspaceCreationSnapshot(
+    /// 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?
+        currentSelectedTabId: UUID?,
+        preferredWorkingDirectory: String?,
+        inheritedTerminalFontPoints: Float?
     ) -> WorkspaceCreationSnapshot {
         let tabSnapshots = currentTabs.map { WorkspaceCreationTabSnapshot(workspace: $0) }
         let selectedTabSnapshot = currentSelectedTabId.flatMap { selectedTabId in
             tabSnapshots.first(where: { $0.id == selectedTabId })
         }
-        let selectedWorkspace = currentSelectedTabId.flatMap { selectedTabId in
-            currentTabs.first(where: { $0.id == selectedTabId })
-        }
 
         return WorkspaceCreationSnapshot(
             tabs: tabSnapshots,
             selectedTabId: currentSelectedTabId,
             selectedTabWasPinned: selectedTabSnapshot?.isPinned ?? false,
-            preferredWorkingDirectory: preferredWorkingDirectoryForNewTab(workspace: selectedWorkspace),
-            inheritedTerminalFontPoints: inheritedTerminalFontPointsForNewWorkspace(workspace: selectedWorkspace)
+            preferredWorkingDirectory: preferredWorkingDirectory,
+            inheritedTerminalFontPoints: inheritedTerminalFontPoints
         )
     }
 
     private func workspaceCreationSnapshot() -> WorkspaceCreationSnapshot {
-        workspaceCreationSnapshot(
+        workspaceCreationSnapshotLite(
             currentTabs: tabs,
-            currentSelectedTabId: selectedTabId
+            currentSelectedTabId: selectedTabId,
+            preferredWorkingDirectory: preferredWorkingDirectoryForNewTab(),
+            inheritedTerminalFontPoints: inheritedTerminalFontPointsForNewWorkspace()
         )
     }
 
@@ -2291,6 +2301,10 @@ class TabManager: ObservableObject {
         return nil
     }
 
+    private func inheritedTerminalFontPointsForNewWorkspace() -> Float? {
+        inheritedTerminalFontPointsForNewWorkspace(workspace: selectedWorkspace)
+    }
+
     private func inheritedTerminalFontPointsForNewWorkspace(
         workspace: Workspace?
     ) -> Float? {

cmuxTests/WorkspaceUnitTests.swift

@@ -448,26 +448,19 @@ final class WorkspaceCreationPlacementTests: XCTestCase {
         XCTAssertEqual(manager.selectedTabId, inserted.id)
     }
 
-    func testAddWorkspaceKeepsCapturedWorkspaceAliveUntilCreationFinishes() {
+    func testAddWorkspaceSurvivesMidCreationClose() {
         let manager = SnapshotMutatingTabManager()
         guard let first = manager.tabs.first else {
             XCTFail("Expected initial workspace")
             return
         }
 
-        var closingWorkspace: Workspace? = manager.addWorkspace()
+        let closingWorkspace = manager.addWorkspace()
         let third = manager.addWorkspace()
         manager.selectWorkspace(third)
 
-        guard let capturedClosingWorkspace = closingWorkspace else {
-            XCTFail("Expected secondary workspace")
-            return
-        }
-
-        let closingWorkspaceId = capturedClosingWorkspace.id
-        weak var weakClosingWorkspace = capturedClosingWorkspace
+        let closingWorkspaceId = closingWorkspace.id
         XCTAssertEqual(manager.tabs.map(\.id), [first.id, closingWorkspaceId, third.id])
-        closingWorkspace = nil
 
         manager.afterCaptureWorkspaceCreationSnapshot = {
             guard let liveWorkspace = manager.tabs.first(where: { $0.id == closingWorkspaceId }) else {
@@ -477,22 +470,11 @@ final class WorkspaceCreationPlacementTests: XCTestCase {
             manager.closeWorkspace(liveWorkspace)
         }
 
-        var didReachBeforeCreateWorkspace = false
-        manager.beforeCreateWorkspace = {
-            didReachBeforeCreateWorkspace = true
-            XCTAssertNotNil(
-                weakClosingWorkspace,
-                "Expected the workspace captured before Cmd+N to stay alive until creation finishes"
-            )
-        }
-
         let inserted = manager.addWorkspace(placementOverride: .afterCurrent)
 
-        XCTAssertTrue(didReachBeforeCreateWorkspace)
         XCTAssertFalse(manager.tabs.contains(where: { $0.id == closingWorkspaceId }))
         XCTAssertEqual(manager.tabs.map(\.id), [first.id, third.id, inserted.id])
         XCTAssertEqual(manager.selectedTabId, inserted.id)
-        XCTAssertNil(weakClosingWorkspace)
     }
 
     func testAddWorkspaceAfterCurrentUsesSnapshotPinnedStateWhenPinningMutatesAfterSnapshot() {