Fix command modified keys. Add plan for splitscreen

Downterm/CommandNotch/Components/TerminalCommandArrowBehavior.swift

@@ -0,0 +1,31 @@
+import AppKit
+import Carbon.HIToolbox
+import SwiftTerm
+
+enum TerminalCommandArrowBehavior {
+    private static let relevantModifiers: NSEvent.ModifierFlags = [.command, .control, .option, .shift]
+    private static let lineKill: [UInt8] = [0x15]
+    private static let clearScreen: [UInt8] = [0x0c]
+
+    static func sequence(
+        for modifierFlags: NSEvent.ModifierFlags,
+        keyCode: UInt16,
+        applicationCursor: Bool
+    ) -> [UInt8]? {
+        let flags = modifierFlags.intersection(relevantModifiers)
+        guard flags == [.command] else { return nil }
+
+        switch Int(keyCode) {
+        case kVK_LeftArrow:
+            return applicationCursor ? EscapeSequences.moveHomeApp : EscapeSequences.moveHomeNormal
+        case kVK_RightArrow:
+            return applicationCursor ? EscapeSequences.moveEndApp : EscapeSequences.moveEndNormal
+        case kVK_Delete:
+            return lineKill
+        case kVK_ANSI_L:
+            return clearScreen
+        default:
+            return nil
+        }
+    }
+}