Add editable untitled Markdown previews

.gitignore

@@ -73,3 +73,7 @@ fastlane/test_output
 
 # Editor bundle build (scripts/editor-bundle)
 node_modules/
+
+# Local design tooling
+.superpowers/
+.worktrees/

Info.plist

@@ -10,7 +10,7 @@
 			<key>CFBundleTypeName</key>
 			<string>Markdown Document</string>
 			<key>CFBundleTypeRole</key>
-			<string>Viewer</string>
+			<string>Editor</string>
 			<key>LSHandlerRank</key>
 			<string>Owner</string>
 			<key>LSItemContentTypes</key>

md-preview/AppDelegate.swift

@@ -93,7 +93,7 @@ private enum AppAppearanceMode: String, CaseIterable {
 }
 
 @main
-final class AppDelegate: NSObject, NSApplicationDelegate {
+final class AppDelegate: NSObject, NSApplicationDelegate, NSMenuItemValidation {
 
     @IBOutlet private weak var checkForUpdatesMenuItem: NSMenuItem?
 
@@ -111,14 +111,14 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
     private weak var darkAppearanceMenuItem: NSMenuItem?
     private weak var normalContentWidthMenuItem: NSMenuItem?
     private weak var fullContentWidthMenuItem: NSMenuItem?
-    private var isOpeningDocumentFromPrompt = false
+    private var undoMenuDefaultTitle = "Undo"
+    private var redoMenuDefaultTitle = "Redo"
     private var isPromptingForDocument = false
-    private var isDocumentPromptScheduled = false
-    private var documentPromptScheduleGeneration = 0
+    private var isUntitledDocumentScheduled = false
+    private var untitledDocumentScheduleGeneration = 0
     private var didReceiveOpenURLsDuringLaunch = false
     private var hasFinishedLaunching = false
     private var pendingOpenURLCount = 0
-    private weak var activeOpenPanel: NSOpenPanel?
     private var isTerminationSaveInProgress = false
     private var pendingTerminationSaveCount = 0
     private var terminationSaveFailed = false
@@ -128,6 +128,7 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
     func applicationDidFinishLaunching(_ notification: Notification) {
         CrashReporter.start()
         applyAppearanceMode(AppAppearanceMode.current, reloadPreviews: false)
+        installUndoMenuItems()
         installAppearanceMenuItems()
         installContentWidthMenuItems()
         installSidebarViewMenuItems()
@@ -140,7 +141,7 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
         installZoomMenuItemIcons()
         hasFinishedLaunching = true
         if !didReceiveOpenURLsDuringLaunch {
-            scheduleDocumentPrompt(requiresNoDocuments: true)
+            scheduleUntitledDocument(requiresNoDocuments: true)
         }
     }
 
@@ -149,13 +150,13 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
     }
 
     func applicationOpenUntitledFile(_ sender: NSApplication) -> Bool {
-        scheduleDocumentPrompt(requiresNoDocuments: true)
+        scheduleUntitledDocument(requiresNoDocuments: true)
         return true
     }
 
     func applicationShouldHandleReopen(_ sender: NSApplication, hasVisibleWindows flag: Bool) -> Bool {
         if !flag {
-            scheduleDocumentPrompt(requiresNoDocuments: true)
+            scheduleUntitledDocument(requiresNoDocuments: true)
             return false
         }
         return true
@@ -165,7 +166,7 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
         if !hasFinishedLaunching {
             didReceiveOpenURLsDuringLaunch = true
         }
-        cancelScheduledDocumentPrompt()
+        cancelScheduledUntitledDocument()
 
         for url in urls {
             if url.isExistingDirectory {
@@ -182,7 +183,7 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
                 guard let self else { return }
                 self.pendingOpenURLCount -= 1
                 if error != nil, self.pendingOpenURLCount == 0 {
-                    self.scheduleDocumentPrompt(requiresNoDocuments: true)
+                    self.scheduleUntitledDocument(requiresNoDocuments: true)
                 }
             }
         }
@@ -261,6 +262,22 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
         activeDocumentWindowController?.handleFindAction(sender)
     }
 
+    @objc private func performUndo(_ sender: Any?) {
+        if let editor = undoTargetEditor {
+            editor.exec("undo")
+        } else {
+            undoTargetManager?.undo()
+        }
+    }
+
+    @objc private func performRedo(_ sender: Any?) {
+        if let editor = undoTargetEditor {
+            editor.exec("redo")
+        } else {
+            undoTargetManager?.redo()
+        }
+    }
+
     @objc private func hideSidebarFromMenu(_ sender: Any?) {
         activeDocumentWindowController?.hideSidebarFromMenu(sender)
         syncSidebarViewMenuState()
@@ -316,6 +333,22 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
             return activeDocumentWindowController?.canToggleEditMode ?? false
         case #selector(formatMarkdownFromMenu(_:)):
             return activeDocumentWindowController?.canFormatMarkdown ?? false
+        case #selector(performUndo(_:)):
+            if let editor = undoTargetEditor {
+                menuItem.title = undoMenuDefaultTitle
+                return editor.canUndo
+            }
+            let undoManager = undoTargetManager
+            menuItem.title = undoManager?.undoMenuItemTitle ?? undoMenuDefaultTitle
+            return undoManager?.canUndo ?? false
+        case #selector(performRedo(_:)):
+            if let editor = undoTargetEditor {
+                menuItem.title = redoMenuDefaultTitle
+                return editor.canRedo
+            }
+            let redoManager = undoTargetManager
+            menuItem.title = redoManager?.redoMenuItemTitle ?? redoMenuDefaultTitle
+            return redoManager?.canRedo ?? false
         default:
             return true
         }
@@ -334,53 +367,64 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
             .first
     }
 
+    /// The window that owns Undo/Redo. An attached sheet takes precedence over
+    /// the document blocked behind it, and `keyWindow` is nil while a menu tracks.
+    private var undoWindow: NSWindow? {
+        let window = NSApp.keyWindow ?? NSApp.mainWindow
+        return window?.attachedSheet ?? window
+    }
+
+    /// The editor that should receive Undo/Redo, or nil when AppKit's own
+    /// responder chain owns them (preview mode, a field editor, a sheet).
+    private var undoTargetEditor: EditorViewController? {
+        (undoWindow?.windowController as? DocumentWindowController)?.focusedEditorForUndo
+    }
+
+    private var undoTargetManager: UndoManager? {
+        guard let window = undoWindow else { return nil }
+        return window.firstResponder?.undoManager ?? window.undoManager
+    }
+
     private func promptForDocument() {
         guard !isPromptingForDocument else { return }
         isPromptingForDocument = true
         defer { isPromptingForDocument = false }
 
         let panel = makeOpenPanel()
-        activeOpenPanel = panel
-        defer { activeOpenPanel = nil }
         guard panel.runModal() == .OK, let url = panel.url else { return }
         if url.isExistingDirectory {
             openFolder(url)
             return
         }
 
-        isOpeningDocumentFromPrompt = true
         NSDocumentController.shared.openDocument(withContentsOf: url,
-                                                 display: true) { [weak self] _, _, error in
-            self?.isOpeningDocumentFromPrompt = false
+                                                 display: true) { _, _, error in
             guard let error else { return }
             NSAlert(error: error).runModal()
         }
     }
 
-    private func scheduleDocumentPrompt(requiresNoDocuments: Bool = false) {
-        guard !isPromptingForDocument,
-              !isDocumentPromptScheduled else { return }
-
-        isDocumentPromptScheduled = true
-        documentPromptScheduleGeneration += 1
-        let scheduleGeneration = documentPromptScheduleGeneration
+    private func scheduleUntitledDocument(requiresNoDocuments: Bool = false) {
+        guard !isUntitledDocumentScheduled else { return }
+        isUntitledDocumentScheduled = true
+        untitledDocumentScheduleGeneration += 1
+        let generation = untitledDocumentScheduleGeneration
         DispatchQueue.main.async { [weak self] in
-            guard let self else { return }
-            guard self.documentPromptScheduleGeneration == scheduleGeneration else { return }
-            self.isDocumentPromptScheduled = false
+            guard let self,
+                  self.untitledDocumentScheduleGeneration == generation else { return }
+            self.isUntitledDocumentScheduled = false
             guard !requiresNoDocuments || NSDocumentController.shared.documents.isEmpty else { return }
+            guard !self.isPromptingForDocument else { return }
+            guard self.pendingOpenURLCount == 0 else { return }
             NSApp.activate(ignoringOtherApps: true)
-            self.promptForDocument()
+            NSDocumentController.shared.newDocument(nil)
         }
     }
 
-    private func cancelScheduledDocumentPrompt() {
-        // Dismiss a prompt that already made it past the generation check and
-        // is sitting in runModal() when the open event arrives.
-        activeOpenPanel?.cancel(nil)
-        guard isDocumentPromptScheduled else { return }
-        documentPromptScheduleGeneration += 1
-        isDocumentPromptScheduled = false
+    private func cancelScheduledUntitledDocument() {
+        guard isUntitledDocumentScheduled else { return }
+        untitledDocumentScheduleGeneration += 1
+        isUntitledDocumentScheduled = false
     }
 
     private func openFolder(_ url: URL) {
@@ -629,6 +673,24 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
         }
     }
 
+    // The nib's Undo/Redo know only the window's native undo manager.
+    // Retarget them so a focused CodeMirror editor can expose its own history.
+    private func installUndoMenuItems() {
+        let undoAction = NSSelectorFromString("undo:")
+        let redoAction = NSSelectorFromString("redo:")
+        guard let editMenu = topLevelSubmenu(matching: Self.editMenuTitles),
+              let undoItem = editMenu.items.first(where: { $0.action == undoAction }),
+              let redoItem = editMenu.items.first(where: { $0.action == redoAction })
+        else { return }
+
+        undoMenuDefaultTitle = undoItem.title
+        redoMenuDefaultTitle = redoItem.title
+        undoItem.target = self
+        undoItem.action = #selector(performUndo(_:))
+        redoItem.target = self
+        redoItem.action = #selector(performRedo(_:))
+    }
+
     private func installNewTabMenuItem() {
         guard let fileMenu = topLevelSubmenu(matching: Self.fileMenuTitles),
               fileMenu.items.first(where: {
@@ -1083,6 +1145,7 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
         topLevelMenuItem(matching: titles)?.submenu
     }
 
+    private static let editMenuTitles: Set<String> = ["Edit", "编辑"]
     private static let fileMenuTitles: Set<String> = ["File", "文件"]
     private static let viewMenuTitles: Set<String> = ["View", "显示"]
     private static let windowMenuTitles: Set<String> = ["Window", "窗口"]