macos: AppleScript windows/tabs

Add ScriptWindow and ScriptTab classes to expose window/tab hierarchy
to AppleScript, along with the corresponding sdef definitions.

macos/Sources/Features/AppleScript/ScriptTab.swift

@@ -0,0 +1,85 @@
+import AppKit
+
+/// AppleScript-facing wrapper around a single tab in a scripting window.
+///
+/// `ScriptWindow.tabs` vends these objects so AppleScript can traverse
+/// `window -> tab` without knowing anything about AppKit controllers.
+@MainActor
+@objc(GhosttyScriptTab)
+final class ScriptTab: NSObject {
+    /// Stable identifier used by AppleScript `tab id "..."` references.
+    private let stableID: String
+
+    /// Weak back-reference to the scripting window that owns this tab wrapper.
+    ///
+    /// We only need this for dynamic properties (`index`, `selected`) and for
+    /// building an object specifier path.
+    private weak var window: ScriptWindow?
+
+    /// Live terminal controller for this tab.
+    ///
+    /// This can become `nil` if the tab closes while a script is running.
+    private weak var controller: BaseTerminalController?
+
+    /// Called by `ScriptWindow.tabs` / `ScriptWindow.selectedTab`.
+    ///
+    /// The ID is computed once so object specifiers built from this instance keep
+    /// a consistent tab identity.
+    init(window: ScriptWindow, controller: BaseTerminalController) {
+        self.stableID = Self.stableID(controller: controller)
+        self.window = window
+        self.controller = controller
+    }
+
+    /// Exposed as the AppleScript `id` property.
+    @objc(id)
+    var idValue: String {
+        stableID
+    }
+
+    /// Exposed as the AppleScript `index` property.
+    ///
+    /// Cocoa scripting expects this to be 1-based for user-facing collections.
+    @objc(index)
+    var index: Int {
+        guard let controller else { return 0 }
+        return window?.tabIndex(for: controller) ?? 0
+    }
+
+    /// Exposed as the AppleScript `selected` property.
+    ///
+    /// Powers script conditions such as `if selected of tab 1 then ...`.
+    @objc(selected)
+    var selected: Bool {
+        guard let controller else { return false }
+        return window?.tabIsSelected(controller) ?? false
+    }
+
+    /// Provides Cocoa scripting with a canonical "path" back to this object.
+    override var objectSpecifier: NSScriptObjectSpecifier? {
+        guard let window else { return nil }
+        guard let windowClassDescription = window.classDescription as? NSScriptClassDescription else {
+            return nil
+        }
+        guard let windowSpecifier = window.objectSpecifier else { return nil }
+
+        // This tells Cocoa how to re-find this tab later:
+        // application -> scriptWindows[id] -> tabs[id].
+        return NSUniqueIDSpecifier(
+            containerClassDescription: windowClassDescription,
+            containerSpecifier: windowSpecifier,
+            key: "tabs",
+            uniqueID: stableID
+        )
+    }
+}
+
+extension ScriptTab {
+    /// Stable ID for one tab controller.
+    ///
+    /// Tab identity belongs to `ScriptTab`, so both tab creation and tab ID
+    /// lookups in `ScriptWindow` call this helper.
+    static func stableID(controller: BaseTerminalController) -> String {
+        "tab-\(ObjectIdentifier(controller).hexString)"
+    }
+}