fix(editor): guard Mod-Enter submit against open IME composition (#5231)

The bare-Enter submit path already refuses to fire while view.composing
is true, but Mod-Enter had no such guard. Pressing ⌘↵ while a pinyin/kana
composition is still open submits the document WITHOUT the composed text
— e.g. paste a screenshot, type a Chinese sentence, hit ⌘↵ before the
buffer commits, and the submission carries only the screenshot. Apply the
same composing guard to Mod-Enter.

Co-authored-by: Lambda <lambda@multica.ai>
Co-authored-by: multica-agent <github@multica.ai>

packages/views/editor/extensions/submit-shortcut.test.ts

@@ -25,7 +25,7 @@ describe("createSubmitExtension", () => {
     isActive: () => false,
   } as Partial<Editor>;
 
-  it("Mod-Enter always submits", () => {
+  it("Mod-Enter submits when no composition is open", () => {
     const onSubmit = vi.fn(() => true);
     const shortcuts = getShortcuts(
       createSubmitExtension(onSubmit, { submitOnEnter: false }),
@@ -33,10 +33,24 @@ describe("createSubmitExtension", () => {
     );
 
     expect(shortcuts["Mod-Enter"]).toBeDefined();
-    shortcuts["Mod-Enter"]!();
+    expect(shortcuts["Mod-Enter"]!()).toBe(true);
     expect(onSubmit).toHaveBeenCalledTimes(1);
   });
 
+  it("Mod-Enter is suppressed during IME composition", () => {
+    const onSubmit = vi.fn(() => true);
+    const shortcuts = getShortcuts(
+      createSubmitExtension(onSubmit, { submitOnEnter: false }),
+      {
+        view: { composing: true } as unknown as Editor["view"],
+        isActive: () => false,
+      },
+    );
+
+    expect(shortcuts["Mod-Enter"]!()).toBe(false);
+    expect(onSubmit).not.toHaveBeenCalled();
+  });
+
   it("bare Enter is not bound when submitOnEnter is false", () => {
     const onSubmit = vi.fn(() => true);
     const shortcuts = getShortcuts(

packages/views/editor/extensions/submit-shortcut.ts

@@ -16,7 +16,15 @@ export function createSubmitExtension(
     name: "submitShortcut",
     addKeyboardShortcuts() {
       const shortcuts: Record<string, () => boolean> = {
-        "Mod-Enter": () => onSubmit(),
+        "Mod-Enter": () => {
+          // IME guard — same as Enter below. While a composition is open the
+          // composed text is not in the document yet, so submitting here
+          // would send the doc WITHOUT what the user just typed (e.g. paste
+          // a screenshot, type a pinyin sentence, hit ⌘↵ before the buffer
+          // commits — the submission carries only the screenshot).
+          if (this.editor.view.composing) return false;
+          return onSubmit();
+        },
       };
       if (submitOnEnter) {
         shortcuts.Enter = () => {