Prevent background webview autofocus from stealing focus

Sources/Panels/BrowserPanelView.swift

@@ -3112,6 +3112,11 @@ struct WebViewRepresentable: NSViewRepresentable {
         let webView = panel.webView
         context.coordinator.panel = panel
         context.coordinator.webView = webView
+        Self.applyWebViewFirstResponderPolicy(
+            panel: panel,
+            webView: webView,
+            isPanelFocused: isPanelFocused
+        )
 
         let shouldUseWindowPortal = panel.shouldPreserveWebViewAttachmentDuringTransientHide()
         if shouldUseWindowPortal {
@@ -3359,6 +3364,15 @@ struct WebViewRepresentable: NSViewRepresentable {
         }
     }
 
+    private static func applyWebViewFirstResponderPolicy(
+        panel: BrowserPanel,
+        webView: WKWebView,
+        isPanelFocused: Bool
+    ) {
+        guard let cmuxWebView = webView as? CmuxWebView else { return }
+        cmuxWebView.allowsFirstResponderAcquisition = isPanelFocused && !panel.shouldSuppressWebViewFocus()
+    }
+
     static func dismantleNSView(_ nsView: NSView, coordinator: Coordinator) {
         coordinator.attachRetryWorkItem?.cancel()
         coordinator.attachRetryWorkItem = nil

Sources/Panels/CmuxWebView.swift

@@ -22,6 +22,14 @@ final class CmuxWebView: WKWebView {
     var onContextMenuDownloadStateChanged: ((Bool) -> Void)?
     var contextMenuLinkURLProvider: ((CmuxWebView, NSPoint, @escaping (URL?) -> Void) -> Void)?
     var contextMenuDefaultBrowserOpener: ((URL) -> Bool)?
+    /// Guard against background panes stealing first responder (e.g. page autofocus).
+    /// BrowserPanelView updates this as pane focus state changes.
+    var allowsFirstResponderAcquisition: Bool = true
+
+    override func becomeFirstResponder() -> Bool {
+        guard allowsFirstResponderAcquisition else { return false }
+        return super.becomeFirstResponder()
+    }
 
     override func performKeyEquivalent(with event: NSEvent) -> Bool {
         // Preserve Cmd+Return/Enter for web content (e.g. editors/forms). Do not

cmuxTests/CmuxWebViewKeyEquivalentTests.swift

@@ -99,6 +99,39 @@ final class CmuxWebViewKeyEquivalentTests: XCTestCase {
         XCTAssertTrue(spy.invoked)
     }
 
+    @MainActor
+    func testCanBlockFirstResponderAcquisitionWhenPaneIsUnfocused() {
+        _ = NSApplication.shared
+
+        let window = NSWindow(
+            contentRect: NSRect(x: 0, y: 0, width: 640, height: 420),
+            styleMask: [.titled, .closable],
+            backing: .buffered,
+            defer: false
+        )
+        let container = NSView(frame: window.contentRect(forFrameRect: window.frame))
+        window.contentView = container
+
+        let webView = CmuxWebView(frame: container.bounds, configuration: WKWebViewConfiguration())
+        webView.autoresizingMask = [.width, .height]
+        container.addSubview(webView)
+
+        window.makeKeyAndOrderFront(nil)
+        defer { window.orderOut(nil) }
+
+        webView.allowsFirstResponderAcquisition = true
+        XCTAssertTrue(window.makeFirstResponder(webView))
+
+        _ = window.makeFirstResponder(nil)
+        webView.allowsFirstResponderAcquisition = false
+        XCTAssertFalse(webView.becomeFirstResponder())
+
+        _ = window.makeFirstResponder(webView)
+        if let firstResponderView = window.firstResponder as? NSView {
+            XCTAssertFalse(firstResponderView === webView || firstResponderView.isDescendant(of: webView))
+        }
+    }
+
     private func installMenu(spy: ActionSpy, key: String, modifiers: NSEvent.ModifierFlags) {
         let mainMenu = NSMenu()