fix(mobile): retain oversized composer drafts

src/web/public/keyboard-accessory.js

@@ -654,6 +654,9 @@ const KeyboardAccessoryBar = {
   _composerDrafts: new Map(),
   _composerUploads: new Map(),
   _composerOverlay: null,
+  // Leave room for both six-character bracketed-paste markers under the
+  // WebSocket input frame's 64 KiB character limit.
+  _composerMaxLength: 65524,
 
   /** HTML for simple mode: arrows, commands, Compose, Esc, dismiss */
   _simpleButtons: `
@@ -1193,7 +1196,12 @@ const KeyboardAccessoryBar = {
     // Match xterm's prepareTextForTerminal(): CR keeps embedded newlines inside
     // the single-line input transport and is what terminal.paste() emitted.
     const pasteText = text.replace(/\r?\n/g, '\r');
-    app._sendInputAsync(sessionId, `\x1b[200~${pasteText}\x1b[201~`);
+    const payload = `\x1b[200~${pasteText}\x1b[201~`;
+    if (payload.length > 65536) {
+      app.showToast?.(`Prompt is too long to send (maximum ${this._composerMaxLength.toLocaleString()} characters)`, 'error');
+      return false;
+    }
+    app._sendInputAsync(sessionId, payload);
     setTimeout(() => app._sendInputAsync(sessionId, '\r', { useMux: true }), 120);
     return true;
   },

test/mobile-prompt-composer.test.ts

@@ -269,6 +269,21 @@ describe('mobile prompt composer', () => {
     expect(app._echoPassthroughSessions.has('session-2')).toBe(true);
   });
 
+  it('keeps an oversized prompt as a draft instead of queueing a rejected frame', () => {
+    const { app, bar, document } = loadComposer();
+    bar.composePrompt();
+    const input = textarea(document);
+    input.value = 'x'.repeat(65525);
+    input.dispatchEvent(new document.defaultView!.Event('input', { bubbles: true }));
+
+    (document.querySelector('.paste-send') as HTMLButtonElement).click();
+
+    expect(app._sendInputAsync).not.toHaveBeenCalled();
+    expect(app.showToast).toHaveBeenCalledWith(expect.stringContaining('too long'), 'error');
+    expect(document.querySelector('.prompt-composer-overlay')).not.toBeNull();
+    expect(bar._composerDrafts.get('session-1')).toHaveLength(65525);
+  });
+
   it('preserves the draft and focuses xterm when Use terminal keyboard is chosen', () => {
     const { app, bar, document, localEcho, runTimers } = loadComposer();
     const composeButton = mountComposeButton(bar, document);