From 3b2a1c30dec851a0ad160d8c56119874faf73e17 Mon Sep 17 00:00:00 2001
From: Lawrence Chen <54008264+lawrencecchen@users.noreply.github.com>
Date: Wed, 11 Mar 2026 18:10:12 -0700
Subject: [PATCH 1/2] Add browser slot responder crash regression test

---
 cmuxTests/CmuxWebViewKeyEquivalentTests.swift | 44 ++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/cmuxTests/CmuxWebViewKeyEquivalentTests.swift b/cmuxTests/CmuxWebViewKeyEquivalentTests.swift
index 3db83f10..51b1afb1 100644
--- a/cmuxTests/CmuxWebViewKeyEquivalentTests.swift
+++ b/cmuxTests/CmuxWebViewKeyEquivalentTests.swift
@@ -2434,7 +2434,9 @@ final class BrowserSessionHistoryRestoreTests: XCTestCase {
 
 @MainActor
 final class BrowserDeveloperToolsVisibilityPersistenceTests: XCTestCase {
-    private final class WKInspectorProbeView: NSView {}
+    private final class WKInspectorProbeView: NSView {
+        override var acceptsFirstResponder: Bool { true }
+    }
 
     private final class FakeInspector: NSObject {
         private(set) var attachCount = 0
@@ -11515,6 +11517,46 @@ final class BrowserWindowPortalLifecycleTests: XCTestCase {
         )
     }
 
+    func testHidingBrowserSlotYieldsOwnedInspectorFirstResponder() {
+        let window = NSWindow(
+            contentRect: NSRect(x: 0, y: 0, width: 520, height: 320),
+            styleMask: [.titled, .closable],
+            backing: .buffered,
+            defer: false
+        )
+        defer { window.orderOut(nil) }
+        realizeWindowLayout(window)
+
+        guard let contentView = window.contentView else {
+            XCTFail("Expected content view")
+            return
+        }
+
+        let slot = WindowBrowserSlotView(frame: NSRect(x: 40, y: 24, width: 260, height: 180))
+        contentView.addSubview(slot)
+
+        let inspectorContainer = NSView(frame: slot.bounds)
+        inspectorContainer.autoresizingMask = [.width, .height]
+        let inspectorView = WKInspectorProbeView(frame: inspectorContainer.bounds)
+        inspectorView.autoresizingMask = [.width, .height]
+        inspectorContainer.addSubview(inspectorView)
+        slot.addSubview(inspectorContainer)
+        contentView.layoutSubtreeIfNeeded()
+
+        XCTAssertTrue(
+            window.makeFirstResponder(inspectorView),
+            "Precondition failed: inspector probe should become first responder"
+        )
+        XCTAssertTrue(window.firstResponder === inspectorView)
+
+        slot.isHidden = true
+
+        XCTAssertNil(
+            window.firstResponder,
+            "Hiding a browser slot should yield any owned inspector responder before it goes off-screen"
+        )
+    }
+
     func testHiddenPortalSyncDoesNotStealLocallyHostedDevToolsWebViewDuringResize() {
         let window = NSWindow(
             contentRect: NSRect(x: 0, y: 0, width: 520, height: 320),

From fce5545675accd158167102f1722db9c1cc09908 Mon Sep 17 00:00:00 2001
From: Lawrence Chen <54008264+lawrencecchen@users.noreply.github.com>
Date: Wed, 11 Mar 2026 18:10:27 -0700
Subject: [PATCH 2/2] Yield hidden browser slot responders

---
 Sources/BrowserWindowPortal.swift | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/Sources/BrowserWindowPortal.swift b/Sources/BrowserWindowPortal.swift
index 200a9ef0..92ba0fe0 100644
--- a/Sources/BrowserWindowPortal.swift
+++ b/Sources/BrowserWindowPortal.swift
@@ -1530,6 +1530,12 @@ final class BrowserPaneDropTargetView: NSView {
 
 final class WindowBrowserSlotView: NSView {
     override var isOpaque: Bool { false }
+    override var isHidden: Bool {
+        didSet {
+            guard isHidden, !oldValue, let window else { return }
+            yieldOwnedFirstResponderIfNeeded(in: window, reason: "slotHidden")
+        }
+    }
     private let paneDropTargetView = BrowserPaneDropTargetView(frame: .zero)
     private let dropZoneOverlayView = BrowserDropZoneOverlayView(frame: .zero)
     private var searchOverlayHostingView: NSHostingView<BrowserSearchOverlay>?
@@ -1571,6 +1577,13 @@ final class WindowBrowserSlotView: NSView {
         nil
     }
 
+    override func viewWillMove(toWindow newWindow: NSWindow?) {
+        if newWindow == nil, let currentWindow = window {
+            yieldOwnedFirstResponderIfNeeded(in: currentWindow, reason: "slotWillLeaveWindow")
+        }
+        super.viewWillMove(toWindow: newWindow)
+    }
+
     override func layout() {
         super.layout()
         paneDropTargetView.frame = bounds
@@ -1739,6 +1752,23 @@ final class WindowBrowserSlotView: NSView {
         return window.makeFirstResponder(nil)
     }
 
+    @discardableResult
+    private func yieldOwnedFirstResponderIfNeeded(in window: NSWindow, reason: String) -> Bool {
+        guard let firstResponder = window.firstResponder,
+              let owningView = firstResponder.browserPortalOwningView,
+              owningView === self || owningView.isDescendant(of: self) else {
+            return false
+        }
+#if DEBUG
+        dlog(
+            "browser.slot.firstResponder.yield reason=\(reason) " +
+            "slot=\(browserPortalDebugToken(self)) " +
+            "responder=\(String(describing: type(of: firstResponder)))"
+        )
+#endif
+        return window.makeFirstResponder(nil)
+    }
+
     func pinHostedWebView(_ webView: WKWebView) {
         guard webView.superview === self else { return }