fix: batch note formatting to prevent typing flashes

Tests/ConjureKitTests/NotesMarkupTests.swift

@@ -41,6 +41,57 @@ func noteFormattingHidesSyntaxButPreservesMarkdownAndLiteralCode() throws {
     #expect(reloaded.contents.string == source)
 }
 
+private final class NotesLayoutProbe: NSLayoutManager {
+    var observeFormatting: ((NSTextStorage) -> Void)?
+
+    override func processEditing(for textStorage: NSTextStorage, edited editMask: NSTextStorageEditActions,
+                                 range newCharRange: NSRange, changeInLength delta: Int,
+                                 invalidatedRange invalidatedCharRange: NSRange) {
+        observeFormatting?(textStorage)
+        super.processEditing(for: textStorage, edited: editMask, range: newCharRange,
+                             changeInLength: delta, invalidatedRange: invalidatedCharRange)
+    }
+}
+
+@Test @MainActor
+func typingDoesNotExposeUnformattedExistingTextToLayout() throws {
+    _ = NSApplication.shared
+    let suite = "NotesFlashing.\(UUID().uuidString)"
+    let defaults = try #require(UserDefaults(suiteName: suite))
+    let directory = FileManager.default.temporaryDirectory.appendingPathComponent(suite)
+    defer {
+        defaults.removePersistentDomain(forName: suite)
+        try? FileManager.default.removeItem(at: directory)
+    }
+    let store = try NotesStore(directory: directory)
+    let id = try store.create()
+    try store.update(id: id, contents: NSAttributedString(string: "# Heading\n- [ ] Task\nPlain"))
+    defaults.set(id.uuidString, forKey: "selectedNote")
+    let controller = NotesController(defaults: defaults, directory: directory)
+    let window = NSWindow(contentRect: NSRect(x: 0, y: 0, width: 570, height: 404),
+                          styleMask: .borderless, backing: .buffered, defer: false)
+    window.contentViewController = controller
+    defer { _ = controller.close(); window.orderOut(nil) }
+    func descendants(_ view: NSView) -> [NSView] { [view] + view.subviews.flatMap(descendants) }
+    let editor = try #require(descendants(controller.view).compactMap { $0 as? NotesTextView }.first)
+    let layout = NotesLayoutProbe()
+    try #require(editor.textContainer).replaceLayoutManager(layout)
+    editor.refreshTasks()
+    window.makeFirstResponder(editor)
+    layout.observeFormatting = { storage in
+        let text = storage.string as NSString
+        let heading = text.range(of: "Heading")
+        let task = text.range(of: "Task")
+        #expect((storage.attribute(.font, at: heading.location, effectiveRange: nil) as? NSFont)?.pointSize == 26)
+        #expect((storage.attribute(.paragraphStyle, at: task.location, effectiveRange: nil) as? NSParagraphStyle)?.headIndent == 22)
+        #expect(storage.attribute(MarkdownHighlighting.hiddenMarkup, at: 0, effectiveRange: nil) as? Bool == true)
+    }
+    defer { layout.observeFormatting = nil }
+    editor.insertText("!", replacementRange: NSRange(location: editor.string.utf16.count, length: 0))
+    #expect(editor.markdownString == "# Heading\n- [ ] Task\nPlain!")
+    #expect(try NotesStore(directory: directory).notes.first?.contents.string == editor.markdownString)
+}
+
 @Test @MainActor
 func noteImagesRenderRoundedWithoutChangingSavedImageData() throws {
     _ = NSApplication.shared
@@ -196,8 +247,6 @@ func notesFormattingShortcutsToggleCombinedStylesAndRespectPopupFocus() throws {
     #expect(try shortcut("b"))
     #expect(editor.markdownString == "fox 🦊")
 
-    let hide = try #require(descendants(content).compactMap { $0 as? NSButton }.first { $0.toolTip == "Hide formatting" })
-    hide.performClick(nil)
     #expect(try shortcut("x", shift: true))
     #expect(editor.markdownString == "~~fox 🦊~~")
     #expect(try shortcut("x", shift: true))