fix(mobile): CJK input loss — IME state machine, focus routing, and Android InputConnection recovery

Three independent root causes of intermittent Chinese character loss
(English was unaffected because it bypasses the composition path):

1. input-cjk.js state machine: stuck _composing when compositionend never
   fires (WeChat/Sogou IMEs) silently swallowed all input; the deferred
   compositionend flush could reset the textarea mid-next-composition
   (cancels the live IME composition on iOS); the 100ms keydown-echo
   window discarded ANY input regardless of content.

2. Focus stealing: session-select / SSE-reconnect paths call
   terminal.focus() (15+ call sites), landing focus on xterm's hidden
   textarea; with the CJK onData gate active, everything typed there was
   swallowed. Fix: focus router in initTerminal routes ALL
   terminal.focus() calls to the CJK field while it is visible, plus a
   self-healing onData gate that reclaims focus when it swallows input.

3. Android InputConnection wedge (9-key IMEs + Chromium): the keyboard
   composes in its own UI but delivers zero DOM events. Fix: skip
   redundant textarea value/selection writes (they race IME session
   setup), and re-tapping the focused empty field forces a blur→focus
   cycle that restarts the input session.

Diagnostics: input-cjk.js now traces every IME event/flush decision into
the crash-diag breadcrumbs; /api/crash-diag stores beacons per page-load
id (iOS PWA reloads no longer wipe the trail, concurrent clients no
longer clobber each other) and flushes on visibilitychange.

Tests: test/input-cjk.test.ts (vm-sandbox, 9 cases incl. regression
guards for all three root causes).

src/web/public/app.js

@@ -61,6 +61,10 @@
 const _crashDiag = {
   _entries: [],
   _maxEntries: 50,
+  // Per-page-load id: the server keys beacons by it, so a reload (fresh id)
+  // archives the previous page's trail instead of overwriting it, and
+  // concurrent clients (desktop + phone) don't clobber each other.
+  _pageId: Date.now().toString(36) + '-' + Math.random().toString(36).slice(2, 8),
   log(msg) {
     const entry = `${new Date().toISOString().slice(11,23)} ${msg}`;
     this._entries.push(entry);
@@ -69,22 +73,36 @@ const _crashDiag = {
   }
 };
 
-// Log previous crash breadcrumbs on startup
+// Log previous crash breadcrumbs on startup, and re-beacon them under a
+// distinct page id — an iOS PWA reload wipes the in-memory trail, and without
+// this the fresh page's first beacon would be all the server ever sees.
 try {
   const prev = localStorage.getItem('codeman-crash-diag');
-  if (prev) console.log('[CRASH-DIAG] Previous session breadcrumbs:\n' + prev);
+  if (prev) {
+    console.log('[CRASH-DIAG] Previous session breadcrumbs:\n' + prev);
+    navigator.sendBeacon('/api/crash-diag', JSON.stringify({ data: prev, id: _crashDiag._pageId + '-prev' }));
+  }
 } catch {}
 _crashDiag.log('PAGE LOAD');
 
 // Heartbeat: send breadcrumbs to server every 2s so they survive tab freezes.
-setInterval(() => {
+function _crashDiagBeacon() {
   try {
-    localStorage.setItem('codeman-crash-heartbeat', String(Date.now()));
     if (_crashDiag._entries.length > 0) {
-      navigator.sendBeacon('/api/crash-diag', JSON.stringify({ data: _crashDiag._entries.join('\n') }));
+      navigator.sendBeacon('/api/crash-diag', JSON.stringify({ data: _crashDiag._entries.join('\n'), id: _crashDiag._pageId }));
     }
   } catch {}
+}
+setInterval(() => {
+  try { localStorage.setItem('codeman-crash-heartbeat', String(Date.now())); } catch {}
+  _crashDiagBeacon();
 }, 2000);
+// iOS suspends JS the instant the app is backgrounded — entries logged since
+// the last 2s tick would sit unsent until (if ever) the page resumes. Flush
+// immediately on hide so a repro right before an app switch is never lost.
+document.addEventListener('visibilitychange', () => {
+  if (document.visibilityState === 'hidden') _crashDiagBeacon();
+});
 
 window.addEventListener('error', (e) => {
   _crashDiag.log(`ERROR: ${e.message} at ${e.filename}:${e.lineno}`);
@@ -3390,9 +3408,15 @@ class CodemanApp {
     // Close WebSocket for previous session (new one opens after buffer load)
     this._disconnectWs();
 
-    // Clear CJK textarea to prevent sending stale text to the wrong session
-    const cjkEl = document.getElementById('cjkInput');
-    if (cjkEl) cjkEl.value = '';
+    // Clear CJK input to prevent sending stale text to the wrong session.
+    // Must go through CjkInput.clear() — a raw value wipe leaves the module's
+    // pending flush timers armed and drops the phantom char it relies on.
+    if (typeof CjkInput !== 'undefined') {
+      CjkInput.clear();
+    } else {
+      const cjkEl = document.getElementById('cjkInput');
+      if (cjkEl) cjkEl.value = '';
+    }
 
     // Clean up flicker filter state when switching sessions
     this._clearTimer('flickerFilterTimeout');

src/web/public/input-cjk.js

@@ -53,13 +53,36 @@ const CjkInput = (() => {
   let _initialized = false;
   let _composing = false;
   let _flushTimer = null;
+  let _compositionFlushTimer = null;
   let _dictationActive = false;
   let _dictationDecayTimer = null;
   let _keydownSentAt = 0;
+  let _keydownSentText = '';
   const _listeners = {};
 
   const PHANTOM = '​';
 
+  // ── Diagnostic trace (intermittent CJK-loss investigation) ──
+  // In-memory ring buffer of every IME event + flush decision. Mirrored into
+  // the crash-diag breadcrumbs (app.js), which beacon to the server every 2s —
+  // after a repro, `GET /api/crash-diag` shows the exact event sequence.
+  const TRACE_MAX = 200;
+  const _trace = [];
+  function _esc(v) {
+    const s = String(v == null ? '' : v).replace(/​/g, '∅');
+    return JSON.stringify(s.length > 24 ? s.slice(0, 24) + '…' + s.length : s);
+  }
+  function _t(msg) {
+    _trace.push(`${Date.now() % 1000000} ${msg}`);
+    if (_trace.length > TRACE_MAX) _trace.shift();
+    try {
+      // eslint-disable-next-line no-undef
+      if (typeof _crashDiag !== 'undefined') _crashDiag.log('CJK ' + msg);
+    } catch {
+      /* crash-diag unavailable (tests) — ring buffer still records */
+    }
+  }
+
   // Two-tier debounce for non-composition input:
   // - KEYBOARD: short debounce (third-party IMEs like Doubao may not fire
   //   composition events even for keyboard CJK typing)
@@ -93,6 +116,16 @@ const CjkInput = (() => {
   }
 
   function _resetToPhantom() {
+    // Skip redundant writes: every programmatic value/selection mutation can
+    // desync an Android IME's input session (InputConnection) — after which
+    // the keyboard composes in its own UI but NO events ever reach the page.
+    // Only touch the DOM when the content actually differs.
+    if (_textarea.value === PHANTOM) {
+      if (_textarea.selectionStart !== 1 || _textarea.selectionEnd !== 1) {
+        _textarea.setSelectionRange(1, 1);
+      }
+      return;
+    }
     _textarea.value = PHANTOM;
     _textarea.setSelectionRange(1, 1);
   }
@@ -103,7 +136,17 @@ const CjkInput = (() => {
 
   /** Flush textarea: send real text to PTY and reset to phantom */
   function _flush() {
+    // Never flush mid-composition: reading the value would send the IME's
+    // provisional text, and resetting the textarea cancels the in-progress
+    // composition on iOS Safari — silently eating the character being typed.
+    // Any committed-but-unflushed text stays in the textarea and is sent
+    // together by the next compositionend flush.
+    if (_composing) {
+      _t('flush SKIP composing');
+      return;
+    }
     const val = _strip(_textarea.value);
+    _t(`flush ${val ? 'send ' + _esc(val) : 'empty'}`);
     if (val) {
       _send(val);
     }
@@ -150,12 +193,31 @@ const CjkInput = (() => {
 
       _resetToPhantom();
 
+      _t('init v2-trace');
+
       _listeners.mousedown = (e) => { e.stopPropagation(); };
+
+      // ── Wedged-IME recovery (Android) ──
+      // Some Android IMEs (esp. 9-key Sogou/Xiaomi/Baidu) can wedge their
+      // InputConnection: the keyboard composes in its own candidate bar but
+      // delivers ZERO DOM events to the focused textarea. JS cannot detect
+      // this (nothing fires) — but re-tapping the already-focused empty field
+      // is the user's natural "it's stuck" gesture. A blur→focus cycle forces
+      // the browser to restart the IME input session, which un-wedges it.
+      _listeners.pointerdown = () => {
+        if (document.activeElement === _textarea && !_composing && _isEffectivelyEmpty()) {
+          _t('ime-reset (retap)');
+          _textarea.blur();
+          setTimeout(() => _textarea.focus(), 0);
+        }
+      };
       _listeners.focus = () => {
+        _t(`focus val=${_esc(_textarea.value)}`);
         window.cjkActive = true;
         if (!_textarea.value) _resetToPhantom();
       };
       _listeners.blur = () => {
+        _t(`blur composing=${_composing} val=${_esc(_textarea.value)}`);
         // Keep cjkActive while CJK input is visible — iOS dictation and system
         // UI may steal focus temporarily, and clearing the flag during that
         // window lets xterm's onData process duplicated input.
@@ -168,28 +230,38 @@ const CjkInput = (() => {
         _composing = false;
       };
       _textarea.addEventListener('mousedown', _listeners.mousedown);
+      _textarea.addEventListener('pointerdown', _listeners.pointerdown);
       _textarea.addEventListener('focus', _listeners.focus);
       _textarea.addEventListener('blur', _listeners.blur);
 
       // ── Composition tracking (keyboard IME — works for CJK typing) ──
       _listeners.compositionstart = () => {
+        _t(`compstart val=${_esc(_textarea.value)}`);
         _composing = true;
         _cancelDebouncedFlush();
         // Leave textarea.value untouched — programmatic changes during
         // compositionstart cancel the IME composition on iOS Safari.
       };
       _listeners.compositionend = () => {
+        _t(`compend val=${_esc(_textarea.value)}`);
         _composing = false;
         _cancelDebouncedFlush();
         // Defer flush: some Android IMEs haven't committed text to textarea
         // when compositionend fires. setTimeout(0) ensures we read the final value.
-        setTimeout(_flush, 0);
+        // Tracked so destroy() can cancel it; if the next composition starts
+        // before it runs, _flush's _composing guard turns it into a no-op.
+        clearTimeout(_compositionFlushTimer);
+        _compositionFlushTimer = setTimeout(() => {
+          _compositionFlushTimer = null;
+          _flush();
+        }, 0);
       };
       _textarea.addEventListener('compositionstart', _listeners.compositionstart);
       _textarea.addEventListener('compositionend', _listeners.compositionend);
 
       // ── Keydown: special keys work REGARDLESS of composition state ──
       _listeners.keydown = (e) => {
+        _t(`keydown ${_esc(e.key)} kc=${e.keyCode} ic=${e.isComposing} c=${_composing}`);
         if (e.key === 'Enter') {
           e.preventDefault();
           _composing = false;
@@ -246,6 +318,7 @@ const CjkInput = (() => {
           e.preventDefault();
           _send(e.key);
           _keydownSentAt = performance.now();
+          _keydownSentText = e.key;
           _resetToPhantom();
           return;
         }
@@ -254,6 +327,23 @@ const CjkInput = (() => {
 
       // ── Input event: primary path for virtual keyboards + dictation ──
       _listeners.input = (e) => {
+        _t(`input ${e.inputType || '?'} ic=${e.isComposing} c=${_composing} val=${_esc(_textarea.value)}`);
+        // ── Stuck-composition recovery ──
+        // Some IMEs (WeChat/Sogou keyboards) fire compositionstart without a
+        // matching compositionend. A stale _composing=true blocks every flush
+        // below — committed CJK text piles up in the textarea and never
+        // reaches the PTY. When the event itself says composition is over
+        // (isComposing false AND a non-composition inputType), trust it.
+        if (
+          _composing &&
+          e.isComposing === false &&
+          e.inputType !== 'insertCompositionText' &&
+          e.inputType !== 'deleteCompositionText'
+        ) {
+          _t('UNSTICK composing');
+          _composing = false;
+        }
+
         // ── Backspace / delete detection ──
         if (e.inputType === 'deleteContentBackward' || e.inputType === 'deleteWordBackward') {
           if (_composing) return;
@@ -283,11 +373,18 @@ const CjkInput = (() => {
 
         if (_composing) return;
 
-        // Keydown handler already sent this character — just clear the
-        // textarea echo that the IME inserted despite preventDefault.
+        // Keydown handler already sent this character — clear the textarea
+        // echo that the IME inserted despite preventDefault. Content-checked:
+        // only a value matching the sent char is an echo. Anything else (e.g.
+        // an IME committing CJK text right after a keydown-sent char) is real
+        // input and must flow through to the debounced flush, not be dropped.
         if (performance.now() - _keydownSentAt < 100) {
-          _resetToPhantom();
-          return;
+          const cur = _strip(_textarea.value);
+          if (cur === '' || cur === _keydownSentText) {
+            _t('echo-drop');
+            _resetToPhantom();
+            return;
+          }
         }
 
         // Outside composition: keyboard typing or voice dictation.
@@ -301,8 +398,30 @@ const CjkInput = (() => {
       return this;
     },
 
+    /**
+     * Discard pending text and timers (e.g. on session switch, so stale text
+     * can't flush into the wrong session). Restores the phantom so backspace
+     * forwarding keeps working — unlike a raw `textarea.value = ''`.
+     */
+    clear() {
+      if (!_initialized || !_textarea) return;
+      _t('clear (external)');
+      _cancelDebouncedFlush();
+      clearTimeout(_compositionFlushTimer);
+      _compositionFlushTimer = null;
+      _composing = false;
+      _resetToPhantom();
+    },
+
+    /** Diagnostic: recent IME event trace (ring buffer). */
+    getTrace() {
+      return _trace.slice();
+    },
+
     destroy() {
       _cancelDebouncedFlush();
+      clearTimeout(_compositionFlushTimer);
+      _compositionFlushTimer = null;
       clearTimeout(_dictationDecayTimer);
       _dictationActive = false;
       if (_textarea) {

src/web/public/terminal-ui.js

@@ -305,6 +305,25 @@ Object.assign(CodemanApp.prototype, {
       });
     }
 
+    // ── Focus router ──
+    // While the CJK field is visible, EVERY terminal.focus() call must land on
+    // the CJK field instead. Focusing xterm's hidden textarea in CJK mode sends
+    // the IME's output into a black hole: the keyboard composes normally, but
+    // onData is gated by cjkActive, so nothing reaches the field OR the PTY.
+    // Session select / SSE-reconnect restore paths call terminal.focus() and
+    // were silently stealing focus after every app switch on mobile (the
+    // intermittent "Chinese input goes nowhere" bug). One chokepoint here
+    // covers all ~15 call sites plus any future ones.
+    const _xtermFocus = this.terminal.focus.bind(this.terminal);
+    this.terminal.focus = () => {
+      const cjkEl = document.getElementById('cjkInput');
+      if (cjkEl?.classList.contains('cjk-input-visible')) {
+        cjkEl.focus();
+      } else {
+        _xtermFocus();
+      }
+    };
+
     // On mobile Safari, delay initial fit() to allow layout to settle
     // This prevents 0-column terminals caused by fit() running before container is sized
     const isMobileSafari =
@@ -627,7 +646,19 @@ Object.assign(CodemanApp.prototype, {
       // is on, because cjkActive stays true the whole time the field is visible.
       const isMouseReport = /^\x1b\[<\d+;\d+;\d+[Mm]$/.test(data);
       // CJK input has focus — block xterm from sending keystrokes to PTY
-      if (!isMouseReport && (window.cjkActive || document.activeElement?.id === 'cjkInput')) return;
+      if (!isMouseReport && (window.cjkActive || document.activeElement?.id === 'cjkInput')) {
+        // Self-heal: if the CJK field is visible but focus drifted to xterm's
+        // hidden textarea (e.g. something called terminal.focus()), everything
+        // typed lands HERE and is swallowed — keyboard shows the IME composing
+        // while both the CJK field and the terminal stay empty. Route focus
+        // back so the very next keystroke lands in the CJK field again.
+        const cjkEl = document.getElementById('cjkInput');
+        if (cjkEl?.classList.contains('cjk-input-visible') && document.activeElement !== cjkEl) {
+          _crashDiag.log('CJK regain-focus (onData swallowed input)');
+          cjkEl.focus();
+        }
+        return;
+      }
       if (this.activeSessionId) {
         // Filter terminal query replies generated by xterm.js itself.
         // Forwarding them through the WebSocket injects DA/DSR/CPR replies
@@ -1622,7 +1653,11 @@ Object.assign(CodemanApp.prototype, {
   // CJK textarea already provides visual feedback — bypass local echo
   // buffering so each composed word reaches the PTY immediately.
   _handleCjkInput(text) {
-    if (!this.activeSessionId) return;
+    if (!this.activeSessionId) {
+      _crashDiag.log(`CJK send DROP no-session len=${text.length}`);
+      return;
+    }
+    _crashDiag.log(`CJK send→${this.activeSessionId.slice(0, 8)} len=${text.length}`);
     this._sendInputAsync(this.activeSessionId, text);
   },
 

src/web/server.ts

@@ -834,7 +834,13 @@ export class WebServer extends EventEmitter {
     // Keep the body as a RAW STRING and parse it inside the handler — a global
     // text/plain -> JSON parser would let a cross-site "simple request" (no CORS
     // preflight) submit JSON to any route. See security review C2.
-    let _crashBreadcrumbs = '';
+    // Keyed by the client's per-page-load id so (a) a page reload (fresh id)
+    // ARCHIVES the previous page's breadcrumbs instead of overwriting them —
+    // iOS PWA reloads used to wipe the trace of the very bug being chased —
+    // and (b) concurrent clients (desktop + phone) don't clobber each other.
+    // Same id replaces in place (each beacon carries the full ring buffer).
+    const MAX_CRASH_PAGES = 10;
+    const _crashPages = new Map<string, { at: number; data: string }>();
     this.app.addContentTypeParser('text/plain;charset=UTF-8', { parseAs: 'string' }, (_req, body, done) => {
       done(null, body);
     });
@@ -844,17 +850,28 @@ export class WebServer extends EventEmitter {
     this.app.post('/api/crash-diag', (req, reply) => {
       const raw = typeof req.body === 'string' ? req.body : '';
       let data = raw;
+      let pageId = 'legacy';
       try {
-        const parsed = JSON.parse(raw) as { data?: unknown };
+        const parsed = JSON.parse(raw) as { data?: unknown; id?: unknown };
         if (parsed && typeof parsed.data === 'string') data = parsed.data;
+        if (parsed && typeof parsed.id === 'string' && parsed.id) pageId = parsed.id.slice(0, 64);
       } catch {
         /* not JSON — treat the raw beacon text as the breadcrumbs */
       }
-      _crashBreadcrumbs = String(data || '');
+      _crashPages.delete(pageId); // re-insert = move to MRU end
+      _crashPages.set(pageId, { at: Date.now(), data: String(data || '') });
+      if (_crashPages.size > MAX_CRASH_PAGES) {
+        const oldest = _crashPages.keys().next().value;
+        if (oldest !== undefined) _crashPages.delete(oldest);
+      }
       reply.code(204).send();
     });
     this.app.get('/api/crash-diag', (_req, reply) => {
-      reply.code(200).send({ breadcrumbs: _crashBreadcrumbs, timestamp: Date.now() });
+      const pages = [..._crashPages.entries()].map(([id, p]) => ({ id, at: p.at, data: p.data }));
+      const breadcrumbs = pages
+        .map((p) => `═══ page ${p.id} (last beacon ${new Date(p.at).toISOString()}) ═══\n${p.data}`)
+        .join('\n\n');
+      reply.code(200).send({ breadcrumbs, pages, timestamp: Date.now() });
     });
 
     // Register all route modules

test/input-cjk.test.ts

@@ -0,0 +1,241 @@
+/**
+ * @fileoverview Unit tests for the CJK IME input module (input-cjk.js).
+ *
+ * Loads the browser module into a vm sandbox (no real DOM) and drives fake
+ * composition/keydown/input event sequences against a stub textarea.
+ * Focus: the intermittent "Chinese characters silently lost" failure modes —
+ * stuck composition state, deferred flush racing the next composition, and
+ * the keydown-echo suppression window swallowing a real IME commit.
+ */
+import { readFileSync } from 'node:fs';
+import { resolve } from 'node:path';
+import vm from 'node:vm';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+const PHANTOM = '​';
+
+interface FakeTextarea {
+  value: string;
+  valueWrites: number;
+  blur: () => void;
+  focus: () => void;
+  classList: { contains: (c: string) => boolean };
+  setSelectionRange: () => void;
+  addEventListener: (ev: string, fn: (e?: unknown) => void) => void;
+  removeEventListener: (ev: string, fn: (e?: unknown) => void) => void;
+  fire: (ev: string, arg?: Record<string, unknown>) => void;
+}
+
+function makeTextarea(): FakeTextarea {
+  const listeners = new Map<string, Array<(e?: unknown) => void>>();
+  let val = '';
+  return {
+    get value() {
+      return val;
+    },
+    set value(v: string) {
+      this.valueWrites++;
+      val = v;
+    },
+    valueWrites: 0,
+    blur: () => {},
+    focus: () => {},
+    classList: { contains: (c: string) => c === 'cjk-input-visible' },
+    setSelectionRange: () => {},
+    addEventListener: (ev, fn) => {
+      const list = listeners.get(ev) ?? [];
+      listeners.set(ev, [...list, fn]);
+    },
+    removeEventListener: (ev, fn) => {
+      const list = listeners.get(ev) ?? [];
+      listeners.set(
+        ev,
+        list.filter((f) => f !== fn)
+      );
+    },
+    fire(ev, arg = {}) {
+      const base = { preventDefault: () => {}, stopPropagation: () => {}, ...arg };
+      for (const fn of listeners.get(ev) ?? []) fn(base);
+    },
+  };
+}
+
+function loadCjkHarness() {
+  const textarea = makeTextarea();
+  const sent: string[] = [];
+  const windowObj: Record<string, unknown> = {};
+  const documentObj = {
+    getElementById: (id: string) => (id === 'cjkInput' ? textarea : null),
+    activeElement: null as unknown,
+  };
+
+  // Delegating closures so vitest fake timers (which patch the test realm's
+  // globals) govern the vm context's timers/clock too.
+  const context = vm.createContext({
+    window: windowObj,
+    document: documentObj,
+    setTimeout: (fn: () => void, ms?: number) => setTimeout(fn, ms),
+    clearTimeout: (t: ReturnType<typeof setTimeout>) => clearTimeout(t),
+    performance: { now: () => performance.now() },
+    console,
+  });
+
+  const src = readFileSync(resolve(import.meta.dirname, '../src/web/public/input-cjk.js'), 'utf8');
+  vm.runInContext(src, context, { filename: 'input-cjk.js' });
+  const CjkInput = vm.runInContext('CjkInput', context);
+
+  CjkInput.init({ send: (text: string) => sent.push(text) });
+  textarea.fire('focus');
+
+  return { CjkInput, textarea, sent, windowObj, documentObj };
+}
+
+describe('CJK input module', () => {
+  beforeEach(() => {
+    vi.useFakeTimers({ toFake: ['setTimeout', 'clearTimeout', 'Date', 'performance'] });
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it('sends committed text after a normal composition cycle', () => {
+    const { textarea, sent } = loadCjkHarness();
+
+    textarea.fire('compositionstart');
+    textarea.value = PHANTOM + '你好';
+    textarea.fire('input', { isComposing: true, inputType: 'insertCompositionText' });
+    textarea.fire('compositionend');
+    vi.advanceTimersByTime(10);
+
+    expect(sent).toEqual(['你好']);
+    expect(textarea.value).toBe(PHANTOM);
+  });
+
+  it('recovers committed text when compositionend never fires (stuck composition)', () => {
+    const { textarea, sent } = loadCjkHarness();
+
+    // IME fires compositionstart but never compositionend (WeChat/Sogou quirk).
+    textarea.fire('compositionstart');
+    textarea.value = PHANTOM + '你好';
+    // The commit arrives as a plain input event outside composition.
+    textarea.fire('input', { isComposing: false, inputType: 'insertText' });
+    vi.advanceTimersByTime(200);
+
+    expect(sent).toEqual(['你好']);
+  });
+
+  it('does not flush or reset the textarea while the next composition is active', () => {
+    const { textarea, sent } = loadCjkHarness();
+
+    // Word 1 commits; the deferred flush is queued but has not run yet.
+    textarea.fire('compositionstart');
+    textarea.value = PHANTOM + '你好';
+    textarea.fire('compositionend');
+    // Word 2 composition begins immediately (fast continuous typing).
+    textarea.fire('compositionstart');
+    textarea.value = PHANTOM + '你好世界';
+
+    // Deferred flush from word 1 fires now — it must NOT touch the textarea
+    // (a programmatic reset here cancels the live IME composition on iOS).
+    vi.advanceTimersByTime(10);
+    expect(sent).toEqual([]);
+    expect(textarea.value).toBe(PHANTOM + '你好世界');
+
+    textarea.fire('compositionend');
+    vi.advanceTimersByTime(10);
+    expect(sent).toEqual(['你好世界']);
+  });
+
+  it('does not discard an IME commit landing inside the keydown echo window', () => {
+    const { textarea, sent } = loadCjkHarness();
+
+    // English char goes out immediately via keydown.
+    textarea.fire('keydown', { key: 'a', ctrlKey: false, altKey: false, metaKey: false });
+    expect(sent).toEqual(['a']);
+
+    // Within 100ms the IME commits Chinese via a bare input event.
+    vi.advanceTimersByTime(50);
+    textarea.value = PHANTOM + '你好';
+    textarea.fire('input', { isComposing: false, inputType: 'insertText' });
+    vi.advanceTimersByTime(200);
+
+    expect(sent).toEqual(['a', '你好']);
+  });
+
+  it('still suppresses the true textarea echo of a keydown-sent character', () => {
+    const { textarea, sent } = loadCjkHarness();
+
+    textarea.fire('keydown', { key: 'a', ctrlKey: false, altKey: false, metaKey: false });
+    expect(sent).toEqual(['a']);
+
+    // Third-party IME ignored preventDefault — the same char echoes into
+    // the textarea. It must be dropped, not sent twice.
+    vi.advanceTimersByTime(10);
+    textarea.value = PHANTOM + 'a';
+    textarea.fire('input', { isComposing: false, inputType: 'insertText' });
+    vi.advanceTimersByTime(300);
+
+    expect(sent).toEqual(['a']);
+    expect(textarea.value).toBe(PHANTOM);
+  });
+
+  it('re-tapping the focused empty field restarts the IME session (wedged-IME recovery)', () => {
+    const { textarea, documentObj } = loadCjkHarness();
+    documentObj.activeElement = textarea;
+    let blurred = 0;
+    let focused = 0;
+    textarea.blur = () => {
+      blurred++;
+    };
+    textarea.focus = () => {
+      focused++;
+    };
+
+    textarea.fire('pointerdown');
+    expect(blurred).toBe(1);
+    vi.advanceTimersByTime(10);
+    expect(focused).toBe(1);
+
+    // First tap on an unfocused field must NOT cycle (normal focus flow).
+    documentObj.activeElement = null;
+    textarea.fire('pointerdown');
+    expect(blurred).toBe(1);
+  });
+
+  it('skips redundant textarea writes when already reset (Android IME desync guard)', () => {
+    const { CjkInput, textarea } = loadCjkHarness();
+    const before = textarea.valueWrites;
+
+    // Value is already the phantom — external clears (session switch / SSE
+    // reconnect) must not rewrite it, or they race the IME session setup.
+    CjkInput.clear();
+    CjkInput.clear();
+
+    expect(textarea.valueWrites).toBe(before);
+  });
+
+  it('routes terminal.focus() to the CJK field while it is visible (focus router)', () => {
+    // Regression guard for the intermittent "Chinese input goes nowhere" bug:
+    // session-select / SSE-reconnect paths call terminal.focus(), which lands
+    // on xterm's hidden textarea; with the CJK gate active, everything typed
+    // there is swallowed. terminal-ui must (a) route focus() to the CJK field
+    // when visible and (b) self-heal inside the onData gate.
+    const src = readFileSync(resolve(import.meta.dirname, '../src/web/public/terminal-ui.js'), 'utf8');
+
+    expect(src).toContain('Focus router');
+    expect(src).toMatch(/this\.terminal\.focus = \(\) => \{/);
+    expect(src).toContain("cjkEl?.classList.contains('cjk-input-visible')");
+    expect(src).toContain('CJK regain-focus (onData swallowed input)');
+  });
+
+  it('sends text plus carriage return on Enter', () => {
+    const { textarea, sent } = loadCjkHarness();
+
+    textarea.value = PHANTOM + '你好';
+    textarea.fire('keydown', { key: 'Enter' });
+
+    expect(sent).toEqual(['你好\r']);
+    expect(textarea.value).toBe(PHANTOM);
+  });
+});