Fix minimal TUI submitted-line duplicate appearance

src/frontends/tui/minimal.test.ts

@@ -39,6 +39,7 @@ function minimalTuiPrivates(value: MinimalTui): {
   handleCommand: (command: unknown) => Promise<void>;
   handleEscapeAction: () => boolean;
   handleCtrlCPress: (nowMs?: number) => boolean;
+  clearSubmittedPromptLine: () => boolean;
   prompt: (text: string) => Promise<string>;
   rl: {
     once: (event: string, cb: () => void) => void;
@@ -61,6 +62,7 @@ function minimalTuiPrivates(value: MinimalTui): {
     handleCommand: (command: unknown) => Promise<void>;
     handleEscapeAction: () => boolean;
     handleCtrlCPress: (nowMs?: number) => boolean;
+    clearSubmittedPromptLine: () => boolean;
     prompt: (text: string) => Promise<string>;
     rl: {
       once: (event: string, cb: () => void) => void;
@@ -428,6 +430,46 @@ describe('MinimalTui backend command', () => {
 });
 
 describe('MinimalTui prompt cancellation', () => {
+  it('omits leading newline when submitted prompt line was cleared', async () => {
+    const mockSession = {
+      id: 'test',
+      getHistory: () => [],
+      addMessage: vi.fn(),
+      clear: vi.fn(),
+      replaceHistory: vi.fn(),
+    };
+
+    const logSpy = vi.spyOn(console, 'log').mockImplementation(() => {});
+    const writeSpy = vi.spyOn(process.stdout, 'write').mockImplementation(() => true);
+    try {
+      const mockAgent = {
+        process: vi.fn(async () => 'ok'),
+      };
+
+      const tui = new MinimalTui({
+        session: asSession(mockSession),
+        modelClient: asRouter({}),
+        agent: asAgent(mockAgent),
+        systemPrompt: 'test',
+      });
+
+      const clearSpy = vi.fn(() => true);
+      minimalTuiPrivates(tui).clearSubmittedPromptLine = clearSpy;
+
+      await minimalTuiPrivates(tui).handleCommand({ type: 'message', content: 'hello' });
+
+      expect(clearSpy).toHaveBeenCalledOnce();
+      const userHeader = writeSpy.mock.calls
+        .map(([chunk]) => String(chunk))
+        .find((chunk) => chunk.includes('You'));
+      expect(userHeader).toBeDefined();
+      expect(userHeader?.startsWith('\n')).toBe(false);
+    } finally {
+      writeSpy.mockRestore();
+      logSpy.mockRestore();
+    }
+  });
+
   it('cancels an active prompt without closing the TUI', async () => {
     const mockSession = {
       id: 'test',