Fix terminal keys swallowed after opening browser (#45)

* Fix terminal keys (arrows, Ctrl+N/P) swallowed after opening browser

After a browser panel is shown, SwiftUI's internal focus system activates
and its _NSHostingView starts consuming arrow keys and other non-Command
key events via performKeyEquivalent, preventing them from reaching the
terminal's keyDown handler.

Fix: In the NSWindow performKeyEquivalent swizzle, when GhosttyNSView is
the first responder and the event has no Command modifier, route directly
to the terminal's performKeyEquivalent — bypassing SwiftUI's view hierarchy
walk entirely.

Also clear stale browserAddressBarFocusedPanelId when a terminal surface
has focus, preventing Cmd+N from being eaten by omnibar selection logic
after focus transitions away from a browser.

Adds DEBUG-only keyboard event ring buffer (KeyDebugLog) that dumps to
/tmp/cmux-key-debug.log for diagnosing future key routing issues.

* Fix split focus and Cmd+Shift+N swallowed after opening browser

Split focus: capture the source terminal's hostedView before bonsplit
mutates focusedPaneId, so focusPanel moves focus FROM the old pane
instead of from the new pane to itself. Also retry ensureFocus when the
new terminal's view has no window yet (matching the existing retry
pattern for isVisibleInUI).

Cmd+Shift+N: after WKWebView has been in the responder chain, SwiftUI's
internal focus system can intercept Command-key events in the content
view hierarchy (returning true) without firing the CommandGroup action
closure. Fix by dispatching Command-key events directly to NSApp.mainMenu
when the terminal is first responder, bypassing the broken SwiftUI path.
Also add Cmd+Shift+N to handleCustomShortcut so it's customizable and
doesn't depend on SwiftUI menu dispatch at all.

* Unified debug event log: merge key/mouse/focus into /tmp/cmux-debug.log

- Delete KeyDebugLog, MouseDebugLog, klog(), mlog() from AppDelegate
- Replace all klog/mlog calls with dlog() (provided by bonsplit)
- Remove debugLogCallback wiring from Workspace
- Add focus change logging: focus.panel, focus.firstResponder,
  split.created, focus.moveFocus
- Add import Bonsplit where needed for dlog access
- Fix stale drag state on cancelled tab drags (bonsplit submodule)

* Fix split focus stolen by re-entrant becomeFirstResponder during reparenting

During programmatic splits (Cmd+D / Cmd+Shift+D), SwiftUI reparents the old
terminal view, which fires becomeFirstResponder → onFocus → focusPanel for the
OLD panel, stealing focus from the newly created pane.

Add programmaticFocusTargetPanelId guard to suppress re-entrant focusPanel
calls for non-target panels during split creation.

Also document the unified debug event log in CLAUDE.md.

* Clear stale title/favicon when browser navigation fails

When a page fails to load (e.g. connection refused), the tab was still
showing the previous page's title and favicon. Now didFailProvisionalNavigation
resets pageTitle to the failed URL and clears faviconPNGData.

* Fix Cmd+N swallowed by browser omnibar and improve split focus suppression

- Only Ctrl+N/P trigger omnibar navigation, not Cmd+N/P (Cmd+N should
  always create new workspace regardless of address bar focus)
- Move split focus suppression from workspace-level guard to source:
  suppress becomeFirstResponder side-effects (onFocus + ghostty_surface_set_focus)
  directly on the old GhosttyNSView during reparenting, preventing both
  model-level and libghostty-level focus divergence
- Remove programmaticFocusTargetPanelId from Workspace.focusPanel

* Fix omnibar hang, WebView white flash, drag-over-browser, and idle CPU spin

- Omnibar: first click selects all without entering NSTextView tracking loop;
  subsequent clicks have 3s synthetic mouseUp safety net to prevent hang
- WebView: set underPageBackgroundColor to match window so new browsers don't
  flash white before content loads
- Drag/drop: register custom UTType (com.splittabbar.tabtransfer) in Info.plist
  so WKWebView doesn't intercept tab drags; override registerForDraggedTypes
  on CmuxWebView as belt-and-suspenders
- CPU: fix infinite makeFirstResponder loop in controlTextDidEndEditing by
  checking both the text field and its field editor (the actual first responder)

Sources/GhosttyTerminalView.swift

@@ -1496,6 +1496,7 @@ class GhosttyNSView: NSView, NSUserInterfaceValidations {
     var scrollbar: GhosttyScrollbar?
     var cellSize: CGSize = .zero
     var desiredFocus: Bool = false
+    var suppressingReparentFocus: Bool = false
     var tabId: UUID?
     var onFocus: (() -> Void)?
     var onTriggerFlash: (() -> Void)?
@@ -1782,6 +1783,17 @@ class GhosttyNSView: NSView, NSUserInterfaceValidations {
             // If we become first responder before the ghostty surface exists (e.g. during
             // split/tab creation while the surface is still being created), record the desired focus.
             desiredFocus = true
+
+            // During programmatic splits, SwiftUI reparents the old NSView which triggers
+            // becomeFirstResponder. Suppress onFocus + ghostty_surface_set_focus to prevent
+            // the old view from stealing focus and creating model/surface divergence.
+            if suppressingReparentFocus {
+#if DEBUG
+                dlog("focus.firstResponder SUPPRESSED (reparent) surface=\(terminalSurface?.id.uuidString.prefix(5) ?? "nil")")
+#endif
+                return result
+            }
+
             // Always notify the host app that this pane became the first responder so bonsplit
             // focus/selection can converge. Previously this was gated on `surface != nil`, which
             // allowed a mismatch where AppKit focus moved but the UI focus indicator (bonsplit)
@@ -1795,6 +1807,7 @@ class GhosttyNSView: NSView, NSUserInterfaceValidations {
             let deltaMs = (now - lastScrollEventTime) * 1000
             Self.focusLog("becomeFirstResponder: surface=\(terminalSurface?.id.uuidString ?? "nil") deltaSinceScrollMs=\(String(format: "%.2f", deltaMs))")
 #if DEBUG
+            dlog("focus.firstResponder surface=\(terminalSurface?.id.uuidString.prefix(5) ?? "nil")")
             if let terminalSurface {
                 AppDelegate.shared?.recordJumpUnreadFocusIfExpected(
                     tabId: terminalSurface.tabId,
@@ -2248,6 +2261,9 @@ class GhosttyNSView: NSView, NSUserInterfaceValidations {
     // MARK: - Mouse Handling
 
     override func mouseDown(with event: NSEvent) {
+        #if DEBUG
+        dlog("terminal.mouseDown surface=\(terminalSurface?.id.uuidString.prefix(5) ?? "nil")")
+        #endif
         window?.makeFirstResponder(self)
         guard let surface = surface else { return }
         let point = convert(event.locationInWindow, from: nil)
@@ -2504,7 +2520,10 @@ class GhosttyNSView: NSView, NSUserInterfaceValidations {
     }
 
     override func performDragOperation(_ sender: any NSDraggingInfo) -> Bool {
-        insertDroppedPasteboard(sender.draggingPasteboard)
+        #if DEBUG
+        dlog("terminal.fileDrop surface=\(terminalSurface?.id.uuidString.prefix(5) ?? "nil")")
+        #endif
+        return insertDroppedPasteboard(sender.draggingPasteboard)
     }
 }
 
@@ -2903,6 +2922,9 @@ final class GhosttySurfaceScrollView: NSView {
     }
 
     func moveFocus(from previous: GhosttySurfaceScrollView? = nil, delay: TimeInterval? = nil) {
+#if DEBUG
+        dlog("focus.moveFocus to=\(self.surfaceView.terminalSurface?.id.uuidString.prefix(5) ?? "nil")")
+#endif
         let work = { [weak self] in
             guard let self else { return }
             guard let window = self.window else { return }
@@ -3030,6 +3052,16 @@ final class GhosttySurfaceScrollView: NSView {
         }
     }
 
+    /// Suppress the surface view's onFocus callback and ghostty_surface_set_focus during
+    /// SwiftUI reparenting (programmatic splits). Call clearSuppressReparentFocus() after layout settles.
+    func suppressReparentFocus() {
+        surfaceView.suppressingReparentFocus = true
+    }
+
+    func clearSuppressReparentFocus() {
+        surfaceView.suppressingReparentFocus = false
+    }
+
     /// Returns true if the terminal's actual Ghostty surface view is (or contains) the window first responder.
     /// This is stricter than checking `hostedView` descendants, since the scroll view can sometimes become
     /// first responder transiently while focus is being applied.