Anchor textbox autocomplete to the cursor

Sources/App/ShortcutRoutingSupport.swift

@@ -191,6 +191,28 @@ func shouldDispatchTextBoxInputArrowViaFirstResponderKeyDown(
     }
 }
 
+/// Ctrl-N / Ctrl-P navigate the mention-completion popover (and emacs-style line
+/// movement) inside the terminal textbox. Like plain arrows, the window's
+/// `performKeyEquivalent` claims these before they reach the textbox `keyDown`, so
+/// they must be routed to the first responder explicitly. Scoped to the textbox so
+/// terminal/browser Ctrl-N/Ctrl-P are unaffected.
+func shouldDispatchTextBoxInputControlNavViaFirstResponderKeyDown(
+    keyCode: UInt16,
+    firstResponderIsTextBoxInput: Bool,
+    firstResponderHasMarkedText: Bool = false,
+    flags: NSEvent.ModifierFlags
+) -> Bool {
+    guard firstResponderIsTextBoxInput else { return false }
+    guard !firstResponderHasMarkedText else { return false }
+
+    let normalizedFlags = flags
+        .intersection(.deviceIndependentFlagsMask)
+        .subtracting([.numericPad, .function, .capsLock])
+    guard normalizedFlags == [.control] else { return false }
+    // kVK_ANSI_N == 45, kVK_ANSI_P == 35
+    return keyCode == 45 || keyCode == 35
+}
+
 func shouldToggleMainWindowFullScreenForCommandControlFShortcut(
     flags: NSEvent.ModifierFlags,
     chars: String,

Sources/AppDelegate.swift

@@ -15790,6 +15790,7 @@ private var cmuxBrowserArrowForwardingDepth = 0
 private var cmuxBrowserOmnibarMarkedTextForwardingDepth = 0
 private var cmuxCommandPaletteArrowForwardingDepth = 0
 private var cmuxTextBoxInputArrowForwardingDepth = 0
+private var cmuxTextBoxInputControlNavForwardingDepth = 0
 private var cmuxWindowFirstResponderBypassDepth = 0
 private var cmuxFieldEditorOwningWebViewAssociationKey: UInt8 = 0
 
@@ -16614,6 +16615,21 @@ private extension NSWindow {
             return true
         }
 
+        if shouldDispatchTextBoxInputControlNavViaFirstResponderKeyDown(
+            keyCode: event.keyCode,
+            firstResponderIsTextBoxInput: firstResponderIsTextBoxInput,
+            firstResponderHasMarkedText: firstResponderHasMarkedText,
+            flags: event.modifierFlags
+        ) {
+            if cmuxTextBoxInputControlNavForwardingDepth > 0 {
+                return false
+            }
+            cmuxTextBoxInputControlNavForwardingDepth += 1
+            defer { cmuxTextBoxInputControlNavForwardingDepth = max(0, cmuxTextBoxInputControlNavForwardingDepth - 1) }
+            self.firstResponder?.keyDown(with: event)
+            return true
+        }
+
         // Web forms rely on Return/Enter flowing through keyDown. If the original
         // NSWindow.performKeyEquivalent consumes Enter first, submission never reaches
         // WebKit. Route Return/Enter directly to the current first responder and