macos: change config access to evented, derived config like libghostty

Previously, we would access the `ghostty.config` object from anywhere.
The issue with this is that memory lifetime access to the underlying
`ghostty_config_t` was messy. It was easy when the apprt owned every
reference but since automatic theme changes were implemented, this isn't
always true anymore.

To fix this, we move to the same pattern we use internally in the core
of ghostty: whenever the config changes, we handle an event, derive our
desired values out of the config (copy them), and then let the caller
free the config if they want to. This way, we can be sure that any
information we need from the config is always owned by us.

macos/Sources/Features/Terminal/BaseTerminalController.swift

@@ -60,6 +60,9 @@ class BaseTerminalController: NSWindowController,
     /// The previous frame information from the window
     private var savedFrame: SavedFrame? = nil
 
+    /// The configuration derived from the Ghostty config so we don't need to rely on references.
+    private var derivedConfig: DerivedConfig
+
     struct SavedFrame {
         let window: NSRect
         let screen: NSRect
@@ -74,6 +77,7 @@ class BaseTerminalController: NSWindowController,
          surfaceTree tree: Ghostty.SplitNode? = nil
     ) {
         self.ghostty = ghostty
+        self.derivedConfig = DerivedConfig(ghostty.config)
 
         super.init(window: nil)
 
@@ -93,6 +97,11 @@ class BaseTerminalController: NSWindowController,
             selector: #selector(didChangeScreenParametersNotification),
             name: NSApplication.didChangeScreenParametersNotification,
             object: nil)
+        center.addObserver(
+            self,
+            selector: #selector(ghosttyConfigDidChangeBase(_:)),
+            name: .ghosttyConfigDidChange,
+            object: nil)
 
         // Listen for local events that we need to know of outside of
         // single surface handlers.
@@ -191,6 +200,20 @@ class BaseTerminalController: NSWindowController,
         window.setFrame(newFrame, display: true)
     }
 
+    @objc private func ghosttyConfigDidChangeBase(_ notification: Notification) {
+        // We only care if the configuration is a global configuration, not a
+        // surface-specific one.
+        guard notification.object == nil else { return }
+        
+        // Get our managed configuration object out
+        guard let config = notification.userInfo?[
+            Notification.Name.GhosttyConfigChangeKey
+        ] as? Ghostty.Config else { return }
+        
+        // Update our derived config
+        self.derivedConfig = DerivedConfig(config)
+    }
+
     // MARK: Local Events
 
     private func localEventHandler(_ event: NSEvent) -> NSEvent? {
@@ -245,7 +268,7 @@ class BaseTerminalController: NSWindowController,
     func pwdDidChange(to: URL?) {
         guard let window else { return }
 
-        if ghostty.config.macosTitlebarProxyIcon == .visible {
+        if derivedConfig.macosTitlebarProxyIcon == .visible {
             // Use the 'to' URL directly
             window.representedURL = to
         } else {
@@ -255,7 +278,7 @@ class BaseTerminalController: NSWindowController,
 
 
     func cellSizeDidChange(to: NSSize) {
-        guard ghostty.config.windowStepResize else { return }
+        guard derivedConfig.windowStepResize else { return }
         self.window?.contentResizeIncrements = to
     }
 
@@ -563,4 +586,19 @@ class BaseTerminalController: NSWindowController,
         guard let surface = focusedSurface?.surface else { return }
         ghostty.resetTerminal(surface: surface)
     }
+
+    private struct DerivedConfig {
+        let macosTitlebarProxyIcon: Ghostty.MacOSTitlebarProxyIcon
+        let windowStepResize: Bool
+
+        init() {
+            self.macosTitlebarProxyIcon = .visible
+            self.windowStepResize = false
+        }
+
+        init(_ config: Ghostty.Config) {
+            self.macosTitlebarProxyIcon = config.macosTitlebarProxyIcon
+            self.windowStepResize = config.windowStepResize
+        }
+    }
 }