feat(desktop): per-session mid-turn message queue (enqueue-on-inflight, drain-once-per-turn, strip UI)

examples/desktop/README.md

@@ -104,6 +104,17 @@ a toggle), and `context/message` / `steering/message` events surface as
 and why. A `Cancel` button appears mid-turn and cuts the stream via
 `session/cancel`.
 
+The wire accepts only one in-flight prompt per session, so pressing Enter
+while a turn is running **queues** your message instead of erroring: a strip
+above the composer shows one chip per queued message with a `queued N`
+counter, and each chip lets you edit the text inline, delete it, or bump it to
+the front (**send next**). When the turn ends, the head of the queue is sent
+automatically — one message per turn completion — so a burst of follow-ups
+plays out in order without you babysitting each turn. The queue is
+per-session (switching sessions shows that session's queue), survives a
+cancelled turn, and is cleared with a notice if the runtime restarts or you
+switch profiles.
+
 ![](docs/readme-shots/03-chat.png)
 
 #### Session Tree

examples/desktop/scripts/qa-cdp-shoot-msg-queue.mjs

@@ -0,0 +1,243 @@
+// QA verification script for lane-msg-queue. Boots an isolated Electron on
+// its own CDP port, drives the composer message queue entirely through the
+// renderer's `window.__dshRenderer` seam (no live model needed), and captures
+// two screenshots into docs/qa-msg-queue/:
+//
+//   01-inflight-two-queued.png — a turn in flight with TWO messages queued;
+//       the strip shows two chips + a "queued 2" counter.
+//   02-after-turn-end-one-left.png — after turn/end auto-drains the head, the
+//       first queued message appears as a sent bubble and the strip shows one
+//       remaining chip ("queued 1").
+//
+// Isolation follows the 2026-07-18 postmortem baked into
+// scripts/qa-cdp-shoot-nav-optional.mjs:
+//   1. --user-data-dir=<tmp>   isolates Chromium userdata.
+//   2. DSH_DESKTOP_HOME=<tmp>  isolates the main-process config root so we
+//      never write into ~/.dsh-desktop.
+//   3. own CDP port (≥9290)    so a lingering Electron helper from another
+//      lane's shoot can't hijack our DevTools endpoint.
+//
+// Why drive via the seam and not a real prompt: the message-queue behaviour
+// is a pure renderer concern (enqueue-on-inflight + auto-drain on turn/end).
+// `window.__dshRenderer` exposes send() + onSessionEvent() + listMsgQueue()
+// ungated, so we can create an in-flight turn, enqueue two messages, and step
+// the turn to completion deterministically — no daemon round-trip, no model
+// key. The keyless daemon-echo include still boots the runtime so the shell
+// is in its normal chat state.
+
+import { spawn } from 'node:child_process'
+import { existsSync, mkdirSync, writeFileSync, rmSync, statSync } from 'node:fs'
+import { resolve, join } from 'node:path'
+import { setTimeout as sleep } from 'node:timers/promises'
+import { tmpdir } from 'node:os'
+
+const WORKTREE = resolve(process.env.DSH_WORKTREE || process.cwd())
+const PARENT = resolve(process.env.DSH_REPO || '/Users/ziya/harness/dsh-desktop-demo')
+const ELECTRON = join(PARENT, 'node_modules/.bin/electron')
+const CDP_PORT = Number(process.env.DSH_MSG_QUEUE_PORT || 9290)
+const OUTDIR = join(WORKTREE, 'docs/qa-msg-queue')
+
+if (!existsSync(ELECTRON)) {
+  console.error(`electron binary not found at ${ELECTRON}`)
+  process.exit(2)
+}
+mkdirSync(OUTDIR, { recursive: true })
+
+function seedHome(dshHome) {
+  // Minimal keyless overlay + config + onboarded sentinel so the first-run
+  // modal doesn't fire and steal the window / rewrite our seed. daemon-echo
+  // is the keyless demo runtime; we never send a real prompt through it.
+  const seedOverlay = [
+    '# QA msg-queue shoot seed overlay (tmp, per-run).',
+    'plugins:',
+    `  - "@cordisjs/plugin-include":`,
+    `      path: ${join(WORKTREE, 'config/daemon-echo.yml')}`,
+    '',
+  ].join('\n')
+  writeFileSync(join(dshHome, 'user-overlay.cordis.yml'), seedOverlay)
+  writeFileSync(join(dshHome, 'config.json'), JSON.stringify({ role: 'coding', approvalMode: 'never' }, null, 2))
+  writeFileSync(join(dshHome, '.onboarded'), new Date().toISOString())
+}
+
+async function bootElectron(dshHome, userData, port) {
+  const child = spawn(ELECTRON, [
+    `--remote-debugging-port=${port}`,
+    `--user-data-dir=${userData}`,
+    '--disable-gpu',
+    '--no-sandbox',
+    '.',
+  ], {
+    cwd: WORKTREE,
+    env: { ...process.env, DSH_DESKTOP_HOME: dshHome, DSH_MAXIMIZE: '1' },
+    stdio: ['ignore', 'pipe', 'pipe'],
+  })
+  const logs = []
+  child.stdout.on('data', d => logs.push(String(d)))
+  child.stderr.on('data', d => logs.push(String(d)))
+  for (let i = 0; i < 40; i++) {
+    await sleep(500)
+    try {
+      const r = await fetch(`http://localhost:${port}/json/list`)
+      if (r.ok) return { child, logs }
+    } catch {}
+  }
+  child.kill('SIGKILL')
+  console.error('electron CDP did not come up in 20s. logs:\n' + logs.join(''))
+  process.exit(3)
+}
+
+async function newCdp(port) {
+  const targets = await (await fetch(`http://localhost:${port}/json/list`)).json()
+  const target = targets.find(t => t.type === 'page')
+  if (!target) throw new Error('no page target on port ' + port)
+  const ws = new WebSocket(target.webSocketDebuggerUrl)
+  await new Promise((ok, err) => { ws.onopen = ok; ws.onerror = e => err(e) })
+  let id = 1
+  const pending = new Map()
+  ws.onmessage = ev => {
+    const data = typeof ev.data === 'string' ? ev.data : String(ev.data)
+    let msg
+    try { msg = JSON.parse(data) } catch { return }
+    if (msg.id != null && pending.has(msg.id)) {
+      const [ok, err] = pending.get(msg.id); pending.delete(msg.id)
+      if (msg.error) err(new Error(msg.error.message)); else ok(msg.result)
+    }
+  }
+  const call = (m, p = {}, ms = 15000) => new Promise((ok, err) => {
+    const _id = id++
+    const t = setTimeout(() => { pending.delete(_id); err(new Error('cdp timeout: ' + m)) }, ms)
+    pending.set(_id, [v => { clearTimeout(t); ok(v) }, e => { clearTimeout(t); err(e) }])
+    ws.send(JSON.stringify({ id: _id, method: m, params: p }))
+  })
+  const evj = async expr => {
+    const r = await call('Runtime.evaluate', {
+      expression: `(async()=>{try{return (${expr})}catch(e){return {__err:String(e)}}})()`,
+      returnByValue: true, awaitPromise: true,
+    })
+    if (r.exceptionDetails) throw new Error(r.exceptionDetails.exception?.description || r.exceptionDetails.text)
+    return r.result?.value
+  }
+  return { ws, call, evj }
+}
+
+// Clip to the composer footer so the strip is unmistakably in frame (not a
+// giant empty chat pane). Falls back to a full-page shot if the selector
+// isn't found.
+async function shoot(call, evj, name) {
+  const clip = await evj(`
+    (() => {
+      const f = document.querySelector('.composer.composer-shell')
+      if (!f) return null
+      const r = f.getBoundingClientRect()
+      // pad upward so a freshly-sent bubble just above the composer is caught.
+      const top = Math.max(0, r.y - 220)
+      return { x: r.x, y: top, width: r.width, height: (r.bottom - top) + 12, scale: 1 }
+    })()
+  `)
+  const shotArgs = { format: 'png', captureBeyondViewport: true }
+  if (clip) shotArgs.clip = clip
+  const shot = await call('Page.captureScreenshot', shotArgs, 30000)
+  if (!shot || !shot.data) throw new Error('captureScreenshot returned no data')
+  const outPath = join(OUTDIR, name)
+  writeFileSync(outPath, Buffer.from(shot.data, 'base64'))
+  const bytes = statSync(outPath).size
+  console.log(`  wrote ${outPath} (${bytes} bytes)`)
+  if (bytes < 20000) throw new Error(`screenshot ${name} is only ${bytes} bytes (<20KB) — likely blank`)
+  return { path: outPath, bytes }
+}
+
+async function main() {
+  const dshHome = join(tmpdir(), 'dsh-msg-queue-home')
+  const userData = join(tmpdir(), 'dsh-msg-queue-userdata')
+  for (const dir of [dshHome, userData]) {
+    try { rmSync(dir, { recursive: true, force: true }) } catch {}
+    mkdirSync(dir, { recursive: true })
+  }
+  seedHome(dshHome)
+  console.log(`booting on CDP :${CDP_PORT}`)
+  const { child } = await bootElectron(dshHome, userData, CDP_PORT)
+  try {
+    await sleep(1500)
+    const { call, evj } = await newCdp(CDP_PORT)
+    await call('Page.enable')
+
+    // Step 1: create a session, make it active, and open an in-flight turn.
+    // We drive the renderer directly through the always-exposed seam.
+    const setup = await evj(`
+      (async () => {
+        const R = window.__dshRenderer
+        if (!R) return { __err: 'no __dshRenderer seam' }
+        R.ensureSession('qa-mq', { title: 'Message queue demo', header: {}, hasUserMessage: true })
+        await R.selectSession('qa-mq')
+        R.onSessionEvent('qa-mq', { type: 'turn/start', seq: 1 })
+        // Enqueue two follow-ups via the real composer send() path.
+        const input = document.getElementById('input')
+        input.value = 'Summarise the three failing tests'
+        await R.send()
+        input.value = 'Then open a PR with the fix'
+        await R.send()
+        return { active: R.getActiveSessionId(), queued: R.listMsgQueue('qa-mq').map(x => x.text) }
+      })()
+    `)
+    console.log('  setup:', JSON.stringify(setup))
+    if (setup && setup.__err) throw new Error(setup.__err)
+    if (!setup || setup.queued.length !== 2) throw new Error('expected 2 queued messages, got ' + JSON.stringify(setup))
+
+    // Assert the strip is actually visible with two chips before shooting.
+    const stripA = await evj(`
+      (() => {
+        const s = document.getElementById('msg-queue-strip')
+        return {
+          hidden: s.hidden,
+          chips: s.querySelectorAll('.msg-queue-chip').length,
+          counter: (s.querySelector('.msg-queue-count') || {}).textContent || '',
+        }
+      })()
+    `)
+    console.log('  strip (inflight):', JSON.stringify(stripA))
+    if (stripA.hidden || stripA.chips !== 2) throw new Error('strip not showing 2 chips: ' + JSON.stringify(stripA))
+    await sleep(300)
+    const shotA = await shoot(call, evj, '01-inflight-two-queued.png')
+
+    // Step 2: end the turn. turn/end auto-drains exactly one item — the head
+    // renders as an optimistic user bubble and the strip drops to one chip.
+    const drained = await evj(`
+      (async () => {
+        const R = window.__dshRenderer
+        R.onSessionEvent('qa-mq', { type: 'turn/end', seq: 2 })
+        await new Promise(r => setTimeout(r, 60))
+        const bubbles = Array.from(document.querySelectorAll('#stream .msg.user .role-label')).length
+        return { remaining: R.listMsgQueue('qa-mq').map(x => x.text), userBubbles: bubbles }
+      })()
+    `)
+    console.log('  after turn/end:', JSON.stringify(drained))
+    if (!drained || drained.remaining.length !== 1) throw new Error('expected 1 remaining, got ' + JSON.stringify(drained))
+
+    const stripB = await evj(`
+      (() => {
+        const s = document.getElementById('msg-queue-strip')
+        return {
+          hidden: s.hidden,
+          chips: s.querySelectorAll('.msg-queue-chip').length,
+          counter: (s.querySelector('.msg-queue-count') || {}).textContent || '',
+        }
+      })()
+    `)
+    console.log('  strip (after drain):', JSON.stringify(stripB))
+    if (stripB.hidden || stripB.chips !== 1) throw new Error('strip not showing 1 chip after drain: ' + JSON.stringify(stripB))
+    await sleep(300)
+    const shotB = await shoot(call, evj, '02-after-turn-end-one-left.png')
+
+    console.log('\n--- SUMMARY ---')
+    console.log(`inflight (2 queued): ${shotA.path} (${shotA.bytes} bytes)`)
+    console.log(`after drain (1 left): ${shotB.path} (${shotB.bytes} bytes)`)
+  } finally {
+    try { child.kill('SIGKILL') } catch {}
+    for (let i = 0; i < 20; i++) {
+      await sleep(500)
+      try { await fetch(`http://localhost:${CDP_PORT}/json/list`) } catch { break }
+    }
+  }
+}
+
+main().catch(err => { console.error(err); process.exit(1) })

examples/desktop/src/renderer/index.html

@@ -517,6 +517,13 @@
                matching the widget action catalog (see next-actions.js).
                Empty by default; hidden entirely when no suggestions land. -->
           <div id="next-action-chips" class="next-action-chips" hidden></div>
+          <!-- Message queue strip (lane-msg-queue). Hidden until the active
+               session has queued messages. Renderer's renderMsgQueueStrip
+               fills it with one chip per queued message (truncated text,
+               inline-edit, delete, "send next") + a "queued N" counter.
+               Per-session: switching sessions re-renders from that session's
+               queue. See msg-queue-model.js + renderer.js §"message queue". -->
+          <div id="msg-queue-strip" class="msg-queue-strip" hidden aria-live="polite"></div>
           <div class="composer-frame">
             <textarea id="input" rows="3" placeholder="Message DSH… (Enter to send, Shift+Enter for newline)"></textarea>
             <div class="composer-bar">
@@ -1487,6 +1494,7 @@
        drill-down view models. Loaded before subagent-view.js so
        buildInlineSubagentTrace can pick up the drill-down helpers. -->
   <script src="./compact-config-model.js"></script>
+  <script src="./msg-queue-model.js"></script>
   <script src="./subagent-drilldown.js"></script>
   <script src="./context-rail.js"></script>
   <script src="./workflow-view.js"></script>

examples/desktop/src/renderer/msg-queue-model.js

@@ -0,0 +1,142 @@
+// Pure model for the composer message queue (lane-msg-queue).
+//
+// The DSH wire accepts exactly ONE in-flight prompt per session — a second
+// session/prompt while a turn is running fails on the wire. So when the user
+// hits Enter mid-turn we don't drop the text and we don't error: we park it
+// in a per-session FIFO and auto-send the head when the turn completes.
+//
+// This module is the data structure only — no DOM, no wire. The renderer
+// owns the "when to enqueue vs send" decision and the "drain on turn end"
+// timing; this file just holds the queues and enforces their invariants so
+// the ordering/isolation semantics can be locked in `node --test` without an
+// Electron harness.
+//
+// Shape:
+//   queues: Map<sessionId, Array<{ id, text }>>
+// Item ids are monotonic across the whole module (not per-session) so a
+// chip's id is globally unique — the UI keys DOM nodes on it and never has
+// to disambiguate by session.
+//
+// Invariants the renderer relies on:
+//   - FIFO: enqueue appends to the tail; drain pops the head.
+//   - promote(id) moves that item to the head (the "send next" affordance),
+//     so the very next drain sends it regardless of arrival order.
+//   - Per-session isolation: no operation on session A can read, mutate, or
+//     drain session B. A drain of an empty/unknown session returns null.
+//   - Empty / whitespace-only text never enqueues (returns null) — a blank
+//     chip is a trap the user can't tell apart from a real queued message.
+
+'use strict'
+
+function createMsgQueue() {
+  /** @type {Map<string, Array<{id:number,text:string}>>} */
+  const queues = new Map()
+  let _seq = 0
+
+  function nextId() { _seq += 1; return _seq }
+
+  function ensure(sessionId) {
+    let q = queues.get(sessionId)
+    if (!q) { q = []; queues.set(sessionId, q) }
+    return q
+  }
+
+  // Append `text` to sessionId's queue. Returns the new item id, or null if
+  // the text is empty/whitespace-only (never enqueue a blank).
+  function enqueue(sessionId, text) {
+    if (sessionId == null) return null
+    const trimmed = typeof text === 'string' ? text.trim() : ''
+    if (!trimmed) return null
+    const id = nextId()
+    ensure(sessionId).push({ id, text: trimmed })
+    return id
+  }
+
+  // Drop the item with `id` from sessionId's queue. Returns true if removed.
+  function remove(sessionId, id) {
+    const q = queues.get(sessionId)
+    if (!q) return false
+    const i = q.findIndex((it) => it.id === id)
+    if (i < 0) return false
+    q.splice(i, 1)
+    return true
+  }
+
+  // Rewrite the text of an existing queued item. Empty/whitespace text is
+  // rejected (returns false) — the caller should treat that as "delete" if
+  // it wants blank edits to remove the chip. Returns true on success.
+  function update(sessionId, id, text) {
+    const q = queues.get(sessionId)
+    if (!q) return false
+    const trimmed = typeof text === 'string' ? text.trim() : ''
+    if (!trimmed) return false
+    const it = q.find((x) => x.id === id)
+    if (!it) return false
+    it.text = trimmed
+    return true
+  }
+
+  // Move `id` to the head of its session queue (the "send next" affordance).
+  // No-op returning false if the item isn't found; a single-item or
+  // already-head move succeeds (idempotent) and returns true.
+  function promote(sessionId, id) {
+    const q = queues.get(sessionId)
+    if (!q) return false
+    const i = q.findIndex((it) => it.id === id)
+    if (i < 0) return false
+    if (i === 0) return true
+    const [it] = q.splice(i, 1)
+    q.unshift(it)
+    return true
+  }
+
+  // Pop and return the head item ({id,text}) of sessionId's queue, or null
+  // when the queue is empty/unknown. This is the single "send one on turn
+  // end" primitive — the renderer calls it exactly once per turn completion.
+  function drain(sessionId) {
+    const q = queues.get(sessionId)
+    if (!q || q.length === 0) return null
+    return q.shift()
+  }
+
+  // Return a shallow copy of sessionId's queue (safe to render from; callers
+  // can't mutate the live array). Empty array for an unknown session.
+  function list(sessionId) {
+    const q = queues.get(sessionId)
+    return q ? q.map((it) => ({ id: it.id, text: it.text })) : []
+  }
+
+  function size(sessionId) {
+    const q = queues.get(sessionId)
+    return q ? q.length : 0
+  }
+
+  // Empty one session's queue. Returns the number of items dropped.
+  function clear(sessionId) {
+    const q = queues.get(sessionId)
+    if (!q) return 0
+    const n = q.length
+    queues.delete(sessionId)
+    return n
+  }
+
+  // Empty every session's queue (runtime crash / profile switch — the old
+  // session ids are a different namespace against the restarted daemon, so
+  // holding their queued text would send it into the void). Returns total
+  // items dropped across all sessions.
+  function clearAll() {
+    let n = 0
+    for (const q of queues.values()) n += q.length
+    queues.clear()
+    return n
+  }
+
+  return { enqueue, remove, update, promote, drain, list, size, clear, clearAll }
+}
+
+if (typeof module !== 'undefined' && module.exports) {
+  module.exports = { createMsgQueue }
+}
+if (typeof window !== 'undefined') {
+  window.__dshMsgQueueModel = { createMsgQueue }
+}

examples/desktop/src/renderer/renderer.js

@@ -99,6 +99,19 @@ const statusText = document.getElementById('status-text')
 const modelBadge = document.getElementById('model-badge')
 const profileSelect = document.getElementById('profile')
 const newSessionBtn = document.getElementById('new-session')
+const msgQueueStripEl = document.getElementById('msg-queue-strip')
+
+// Composer message queue (lane-msg-queue). The wire accepts one in-flight
+// prompt per session; a mid-turn Enter would otherwise fire a second
+// session/prompt that the daemon rejects. Instead we park the text in a
+// per-session FIFO (msg-queue-model.js) and auto-drain the head when the
+// turn completes. The model is a pure data structure; all DOM + wire timing
+// lives in this file (see §"message queue"). Guarded so a stripped build
+// without the module script simply disables queueing (send stays direct).
+const msgQueue = (typeof window !== 'undefined' && window.__dshMsgQueueModel
+  && typeof window.__dshMsgQueueModel.createMsgQueue === 'function')
+  ? window.__dshMsgQueueModel.createMsgQueue()
+  : null
 
 const state = {
   activeSessionId: null,
@@ -586,6 +599,9 @@ async function selectSession(id) {
   // their seed boundary. During live streaming we grow the same map when
   // subagent.started fires.
   installKnownForkMarkers(id)
+  // Per-session queue: repaint the strip for the session we just switched to.
+  // Strict isolation — the strip only ever shows the active session's queue.
+  renderMsgQueueStrip()
 }
 
 async function replayHistory(id) {
@@ -4856,6 +4872,11 @@ function onSessionEvent(sessionId, event) {
     // without a badge instead of one from the previous turn.
     const startData = event.data || event
     meta.currentTurnTrigger = (startData && startData.trigger) || null
+    // Arm the once-per-turn queue drain. turn/end and session.finished both
+    // signal completion (a clean turn emits turn/end; an errored/cancelled
+    // turn may arrive only as session.finished). Whichever fires first
+    // consumes this flag so the queue drains exactly one item per turn.
+    meta._turnDrainPending = true
     if (sessionId === state.activeSessionId) { state.inflightTurn = true; updateCancelButton(); updateCompactButton(); updateForkButtons() }
     renderSessionList()
   }
@@ -4864,6 +4885,11 @@ function onSessionEvent(sessionId, event) {
     meta.currentTurnTrigger = null
     if (sessionId === state.activeSessionId) { state.inflightTurn = false; updateCancelButton(); updateCompactButton(); updateForkButtons() }
     renderSessionList()
+    // Auto-drain one queued message for this session now that its turn is
+    // done. Fires for the exact turn-completion condition that re-enables
+    // Cancel; a cancelled turn ends with turn/end too, so the queue drains
+    // there just like a clean completion (queue survives Cancel by design).
+    void drainMsgQueueOnce(sessionId)
   }
   if (event.time && event.time > meta.lastEventTime) meta.lastEventTime = event.time
   // §1.1 trace bucket: non-boundary events get bucketed into
@@ -6071,9 +6097,133 @@ function onInterruptInvalidate({ interruptId, reason }) {
 
 // -- send / cancel -----------------------------------------------------------
 
+// -- message queue ----------------------------------------------------------
+//
+// Renders the strip above the composer for the ACTIVE session's queue. The
+// strip is hidden when the queue is empty; each queued message is one chip
+// with truncated text (click to inline-edit), a "send next" (promote) button,
+// and a delete (×). A "queued N" counter badge leads the row. Per-session:
+// selectSession + every mutation calls this, so switching sessions shows that
+// session's queue and nothing bleeds across sessions.
+
+const MSG_QUEUE_CHIP_MAX = 48
+
+// Truncate for the chip label. Kept in sync with MSG_QUEUE_CHIP_MAX; the full
+// text lives on the chip's title attribute so hover reveals the whole thing.
+function truncateQueueText(text) {
+  const t = String(text || '')
+  return t.length > MSG_QUEUE_CHIP_MAX ? t.slice(0, MSG_QUEUE_CHIP_MAX - 1) + '…' : t
+}
+
+// Swap a chip's static label for an inline <input> seeded with the full text.
+// Enter / blur commits via msgQueue.update (blank ⇒ delete, matching the
+// model's "never keep a blank" rule); Escape re-renders to cancel.
+function beginQueueChipEdit(sessionId, id, chipEl, fullText) {
+  if (!chipEl) return
+  const input = document.createElement('input')
+  input.type = 'text'
+  input.className = 'msg-queue-chip-edit'
+  input.value = fullText
+  let done = false
+  const commit = (save) => {
+    if (done) return
+    done = true
+    if (save) {
+      const v = input.value.trim()
+      if (!v) msgQueue.remove(sessionId, id)
+      else msgQueue.update(sessionId, id, v)
+    }
+    renderMsgQueueStrip()
+  }
+  input.addEventListener('keydown', (e) => {
+    if (e.key === 'Enter') { e.preventDefault(); commit(true) }
+    else if (e.key === 'Escape') { e.preventDefault(); commit(false) }
+  })
+  input.addEventListener('blur', () => commit(true))
+  chipEl.textContent = ''
+  chipEl.appendChild(input)
+  input.focus()
+}
+
+function makeQueueChip(sessionId, item) {
+  const chip = document.createElement('span')
+  chip.className = 'msg-queue-chip'
+  chip.dataset.queueId = String(item.id)
+
+  const label = document.createElement('button')
+  label.type = 'button'
+  label.className = 'msg-queue-chip-text'
+  label.textContent = truncateQueueText(item.text)
+  label.title = item.text + '\n(click to edit)'
+  label.addEventListener('click', () => beginQueueChipEdit(sessionId, item.id, chip, item.text))
+
+  // "send next" — promote to head so the next drain sends this item first.
+  const promoteBtn = document.createElement('button')
+  promoteBtn.type = 'button'
+  promoteBtn.className = 'msg-queue-chip-btn msg-queue-chip-promote'
+  promoteBtn.title = 'Send this one next'
+  promoteBtn.setAttribute('aria-label', 'Send this message next')
+  promoteBtn.textContent = '↑'
+  promoteBtn.addEventListener('click', () => { msgQueue.promote(sessionId, item.id); renderMsgQueueStrip() })
+
+  const delBtn = document.createElement('button')
+  delBtn.type = 'button'
+  delBtn.className = 'msg-queue-chip-btn msg-queue-chip-del'
+  delBtn.title = 'Remove from queue'
+  delBtn.setAttribute('aria-label', 'Remove queued message')
+  delBtn.textContent = '×'
+  delBtn.addEventListener('click', () => { msgQueue.remove(sessionId, item.id); renderMsgQueueStrip() })
+
+  chip.append(label, promoteBtn, delBtn)
+  return chip
+}
+
+function renderMsgQueueStrip() {
+  if (!msgQueueStripEl || !msgQueue) return
+  const sid = state.activeSessionId
+  const items = sid ? msgQueue.list(sid) : []
+  msgQueueStripEl.textContent = ''
+  if (items.length === 0) {
+    msgQueueStripEl.hidden = true
+    return
+  }
+  msgQueueStripEl.hidden = false
+
+  const badge = document.createElement('span')
+  badge.className = 'msg-queue-count'
+  badge.textContent = `queued ${items.length}`
+  msgQueueStripEl.appendChild(badge)
+
+  // Only the head is a promote target worth showing an active arrow on, but
+  // we render the affordance on every non-head chip; the head chip's arrow is
+  // greyed (already next) via the .is-head class.
+  for (let i = 0; i < items.length; i++) {
+    const chip = makeQueueChip(sid, items[i])
+    if (i === 0) chip.classList.add('is-head')
+    msgQueueStripEl.appendChild(chip)
+  }
+}
+
 async function send() {
   const text = inputEl.value.trim()
   if (!text) return
+  // Mid-turn Enter: the active session already has a prompt in flight (the
+  // wire accepts only one at a time). Park this text in the session's queue
+  // and clear the composer as if sent — it auto-drains on turn/end. Only
+  // applies when there's an active session AND a turn is running; a fresh
+  // "+" session or an idle session falls through to the normal send path.
+  if (msgQueue && state.activeSessionId && state.inflightTurn) {
+    const sid = state.activeSessionId
+    const meta = state.sessions.get(sid)
+    if (meta && !meta.hasUserMessage) {
+      meta.hasUserMessage = true
+      if (!meta.title) meta.title = text.slice(0, 40)
+    }
+    msgQueue.enqueue(sid, text)
+    inputEl.value = ''
+    renderMsgQueueStrip()
+    return
+  }
   if (!state.activeSessionId) {
     const { id } = await window.dsh.newSession()
     ensureSession(id, { title: text.slice(0, 40), hasUserMessage: true })
@@ -6091,22 +6241,66 @@ async function send() {
     }
   }
   const sid = state.activeSessionId
-  // Optimistic bubble — the server echoes user/message shortly after, and the
-  // event handler adopts this element in place instead of re-rendering.
-  appendMessage({ role: 'user', text, optimistic: true })
-  updateEmptyStateVisibility()
-  inputEl.value = ''
-  sendBtn.disabled = true
-  state.inflightTurn = true; updateCancelButton(); updateCompactButton(); updateForkButtons()
+  await dispatchPrompt(sid, text, { clearComposer: true })
+}
+
+// The shared "actually send a prompt" tail: optimistic bubble + inflight
+// flag + sendPrompt, with the existing error surface. Extracted from send()
+// so the queue's auto-drain sends a parked message through the exact same
+// path a live Enter takes. `opts.clearComposer` empties the textarea (live
+// send); the drain path leaves it alone (the user may be mid-typing the next
+// message). The optimistic bubble + inflight flag only apply when `sid` is
+// the active session — a drain firing for a background session's turn/end
+// must not paint into the foreground stream (the echoed user/message renders
+// when that session is next viewed).
+async function dispatchPrompt(sid, text, opts = {}) {
+  const isActive = sid === state.activeSessionId
+  if (isActive) {
+    // Optimistic bubble — the server echoes user/message shortly after, and
+    // the event handler adopts this element in place instead of re-rendering.
+    appendMessage({ role: 'user', text, optimistic: true })
+    updateEmptyStateVisibility()
+    if (opts.clearComposer) inputEl.value = ''
+    sendBtn.disabled = true
+    state.inflightTurn = true; updateCancelButton(); updateCompactButton(); updateForkButtons()
+  }
+  const meta = state.sessions.get(sid)
+  if (meta) meta.running = true
   try {
     await window.dsh.sendPrompt(sid, text)
   } catch (err) {
+    // Surface the error on the stream (matches the live-send path). We do
+    // NOT clear the rest of the queue — a failed drain leaves the remaining
+    // items parked so the user can retry / edit rather than losing them.
     appendSystem(`error: ${err.message}`)
   } finally {
-    sendBtn.disabled = false
+    if (isActive) sendBtn.disabled = false
   }
 }
 
+// Drain exactly one queued message for `sessionId` and send it — guarded so
+// it fires at most once per turn even when both turn/end and
+// session.finished arrive for the same turn. The `_turnDrainPending` flag is
+// armed on turn/start and consumed here. ONE item per turn completion, so
+// each queued follow-up waits for its own turn to finish (the head's
+// turn/end drains the next head, and so on). Runs after the completion
+// handler has flipped inflightTurn off, so dispatchPrompt re-arms it for the
+// drained send.
+async function drainMsgQueueOnce(sessionId) {
+  if (!msgQueue) return
+  const meta = state.sessions.get(sessionId)
+  // Guard: only the first completion signal for this turn drains. Absent a
+  // meta (defensive) we still allow one drain.
+  if (meta) {
+    if (!meta._turnDrainPending) return
+    meta._turnDrainPending = false
+  }
+  const next = msgQueue.drain(sessionId)
+  renderMsgQueueStrip()
+  if (!next) return
+  await dispatchPrompt(sessionId, next.text, { clearComposer: false })
+}
+
 async function cancel() {
   if (!state.activeSessionId) return
   try {
@@ -6171,6 +6365,11 @@ window.dsh.onNotify(({ method, params }) => {
     if (params.sessionId === state.activeSessionId) { state.inflightTurn = false; updateCancelButton(); updateForkButtons() }
     // Refresh listing so title/lastEventTime catch up.
     void refreshSessionList()
+    // Drain-once: if this session's turn ended via session.finished without a
+    // clean turn/end (error/cancel paths), the guard fires the single drain
+    // here. If turn/end already drained, `_turnDrainPending` is false and this
+    // is a no-op.
+    void drainMsgQueueOnce(params.sessionId)
   } else if (method === 'subagent.started') {
     // Grow the tree eagerly: register the child session with a placeholder
     // parent link, refresh the sidebar, and drop a fork marker on the parent
@@ -6615,6 +6814,19 @@ window.dsh.onInitialized((info) => {
   titleEl.textContent = 'New chat'
   updateEmptyStateVisibility()
   updateCancelButton()
+  // Runtime crash / profile switch = a fresh session namespace (the old
+  // session ids can never come back). Any messages still queued against the
+  // dead runtime's sessions would send into the void, so wipe every queue
+  // and — if we actually dropped anything — drop a one-line notice so the
+  // user knows their parked follow-ups didn't survive the restart. Mirrors
+  // the interrupt-invalidate posture (stale-against-restart state is a trap).
+  if (msgQueue) {
+    const dropped = msgQueue.clearAll()
+    if (dropped > 0) {
+      appendSystem(`runtime restarted — cleared ${dropped} queued message${dropped === 1 ? '' : 's'}`)
+    }
+    renderMsgQueueStrip()
+  }
   // New runtime = unknown compact support; button falls back to greyed
   // until the first successful call proves the daemon accepts the method
   // (or a MethodNotFound flips it to `false`).
@@ -8211,6 +8423,14 @@ window.__dshRenderer = {
     sessionIds: Array.from(state.sessions.keys()),
     replayingId: state.replayingId,
   }),
+  // Message queue (lane-msg-queue) seam: expose the send entry point, the
+  // pure queue handle, and the strip renderer so renderer-level tests and QA
+  // scripts can walk the enqueue-on-inflight + auto-drain wiring without a
+  // real wire round-trip. `getMsgQueue` returns the live model instance.
+  send,
+  getMsgQueue: () => msgQueue,
+  listMsgQueue: (sid) => (msgQueue ? msgQueue.list(sid) : []),
+  renderMsgQueueStrip,
 }
 
 // `⌘.` (Ctrl-. on non-Mac) toggles every trace-event-row

examples/desktop/src/renderer/style.css

@@ -3673,6 +3673,78 @@ textarea:focus-visible {
   cursor: pointer;
 }
 .composer-model-warn a:hover { color: var(--accent); }
+
+/* Message queue strip (lane-msg-queue). Sits above the composer frame, shown
+   only when the active session has queued mid-turn messages. One chip per
+   queued message + a leading "queued N" counter. Chip grammar mirrors the
+   composer chip pills (999px radius, muted surface, 11.5px label) so it reads
+   as part of the composer, not a separate widget. */
+.msg-queue-strip {
+  display: flex; align-items: center; flex-wrap: wrap;
+  gap: 6px;
+  margin: 0 4px 6px 4px;
+  padding: 4px 2px;
+}
+.msg-queue-count {
+  display: inline-flex; align-items: center;
+  padding: 2px 8px;
+  border-radius: 999px;
+  background: var(--accent-soft);
+  color: var(--accent);
+  font-size: 10.5px; font-weight: 600;
+  letter-spacing: 0.03em;
+  text-transform: uppercase;
+  flex: 0 0 auto;
+}
+.msg-queue-chip {
+  display: inline-flex; align-items: center; gap: 2px;
+  padding: 2px 4px 2px 8px;
+  border-radius: 999px;
+  background: var(--surface-2);
+  border: 1px solid var(--border);
+  max-width: 280px;
+  transition: border-color 120ms ease, background 120ms ease;
+}
+.msg-queue-chip:hover { border-color: var(--accent); }
+.msg-queue-chip-text {
+  border: none; background: transparent;
+  padding: 0; margin: 0;
+  color: var(--text-secondary);
+  font: inherit; font-size: 11.5px; line-height: 1.4;
+  max-width: 200px;
+  overflow: hidden; text-overflow: ellipsis; white-space: nowrap;
+  cursor: text;
+}
+.msg-queue-chip-text:hover { color: var(--text); }
+.msg-queue-chip-edit {
+  border: 1px solid var(--accent);
+  border-radius: var(--radius-sm);
+  background: var(--surface);
+  color: var(--text);
+  font: inherit; font-size: 11.5px; line-height: 1.4;
+  padding: 1px 6px;
+  min-width: 180px;
+  outline: none;
+}
+.msg-queue-chip-btn {
+  display: inline-flex; align-items: center; justify-content: center;
+  width: 18px; height: 18px;
+  padding: 0; border: none;
+  border-radius: 999px;
+  background: transparent;
+  color: var(--text-tertiary);
+  font-size: 13px; line-height: 1;
+  cursor: pointer;
+  transition: background 120ms ease, color 120ms ease;
+}
+.msg-queue-chip-btn:hover { background: var(--surface-hover); color: var(--text); }
+.msg-queue-chip-del:hover { color: var(--err); }
+/* The head chip is already "next" — dim its promote arrow so the affordance
+   reads as inert without removing it (keeps chip layout stable). */
+.msg-queue-chip.is-head .msg-queue-chip-promote {
+  opacity: 0.35;
+  pointer-events: none;
+}
 .composer-chip--mode {
   color: var(--text-secondary);
 }

examples/desktop/test/msg-queue-model.test.js

@@ -0,0 +1,145 @@
+// Unit tests for msg-queue-model.js — the per-session FIFO backing the
+// composer's mid-turn message queue. Pure data structure, no DOM.
+
+'use strict'
+
+const test = require('node:test')
+const assert = require('node:assert/strict')
+
+const { createMsgQueue } = require('../src/renderer/msg-queue-model.js')
+
+test('enqueue returns a monotonic id and list preserves FIFO order', () => {
+  const q = createMsgQueue()
+  const a = q.enqueue('s1', 'first')
+  const b = q.enqueue('s1', 'second')
+  const c = q.enqueue('s1', 'third')
+  assert.ok(a < b && b < c, 'ids are monotonic')
+  assert.deepEqual(q.list('s1').map((x) => x.text), ['first', 'second', 'third'])
+})
+
+test('enqueue trims text and rejects empty / whitespace-only', () => {
+  const q = createMsgQueue()
+  assert.equal(q.enqueue('s1', ''), null)
+  assert.equal(q.enqueue('s1', '   '), null)
+  assert.equal(q.enqueue('s1', '\n\t '), null)
+  const id = q.enqueue('s1', '  hi  ')
+  assert.ok(id)
+  assert.equal(q.list('s1')[0].text, 'hi', 'stored text is trimmed')
+  assert.equal(q.size('s1'), 1, 'rejected blanks never entered the queue')
+})
+
+test('enqueue with null sessionId is a no-op', () => {
+  const q = createMsgQueue()
+  assert.equal(q.enqueue(null, 'x'), null)
+  assert.equal(q.enqueue(undefined, 'x'), null)
+})
+
+test('drain pops the head and returns null when empty/unknown', () => {
+  const q = createMsgQueue()
+  assert.equal(q.drain('s1'), null, 'unknown session drains to null')
+  q.enqueue('s1', 'one')
+  q.enqueue('s1', 'two')
+  assert.equal(q.drain('s1').text, 'one', 'head first')
+  assert.equal(q.drain('s1').text, 'two')
+  assert.equal(q.drain('s1'), null, 'emptied queue drains to null')
+})
+
+test('drain-once semantics: one call removes exactly one item', () => {
+  const q = createMsgQueue()
+  q.enqueue('s1', 'a')
+  q.enqueue('s1', 'b')
+  q.enqueue('s1', 'c')
+  const first = q.drain('s1')
+  assert.equal(first.text, 'a')
+  assert.equal(q.size('s1'), 2, 'the other two wait for their own turn ends')
+  assert.deepEqual(q.list('s1').map((x) => x.text), ['b', 'c'])
+})
+
+test('remove drops a specific item by id; returns false when absent', () => {
+  const q = createMsgQueue()
+  const a = q.enqueue('s1', 'a')
+  const b = q.enqueue('s1', 'b')
+  assert.equal(q.remove('s1', a), true)
+  assert.deepEqual(q.list('s1').map((x) => x.text), ['b'])
+  assert.equal(q.remove('s1', a), false, 'already gone')
+  assert.equal(q.remove('nope', b), false, 'unknown session')
+})
+
+test('update rewrites text, trims, and rejects blank', () => {
+  const q = createMsgQueue()
+  const id = q.enqueue('s1', 'old')
+  assert.equal(q.update('s1', id, '  new  '), true)
+  assert.equal(q.list('s1')[0].text, 'new')
+  assert.equal(q.update('s1', id, '   '), false, 'blank edit rejected')
+  assert.equal(q.list('s1')[0].text, 'new', 'text unchanged after rejected edit')
+  assert.equal(q.update('s1', 9999, 'x'), false, 'unknown id')
+})
+
+test('promote moves an item to the head so the next drain sends it', () => {
+  const q = createMsgQueue()
+  q.enqueue('s1', 'a')
+  const b = q.enqueue('s1', 'b')
+  q.enqueue('s1', 'c')
+  assert.equal(q.promote('s1', b), true)
+  assert.deepEqual(q.list('s1').map((x) => x.text), ['b', 'a', 'c'])
+  assert.equal(q.drain('s1').text, 'b', 'promoted item drains first')
+})
+
+test('promote is idempotent on the head and single-item queues', () => {
+  const q = createMsgQueue()
+  const a = q.enqueue('s1', 'a')
+  assert.equal(q.promote('s1', a), true, 'single item head promote succeeds')
+  assert.deepEqual(q.list('s1').map((x) => x.text), ['a'])
+  const b = q.enqueue('s1', 'b')
+  assert.equal(q.promote('s1', a), true, 'already-head promote succeeds')
+  assert.deepEqual(q.list('s1').map((x) => x.text), ['a', 'b'])
+  assert.equal(q.promote('s1', 4242), false, 'unknown id fails')
+})
+
+test('per-session isolation: operations never cross sessions', () => {
+  const q = createMsgQueue()
+  const a1 = q.enqueue('s1', 's1-a')
+  q.enqueue('s2', 's2-a')
+  q.enqueue('s2', 's2-b')
+  assert.equal(q.size('s1'), 1)
+  assert.equal(q.size('s2'), 2)
+  // drain s1 leaves s2 untouched
+  assert.equal(q.drain('s1').text, 's1-a')
+  assert.equal(q.size('s2'), 2, 's2 unaffected by s1 drain')
+  // remove/promote keyed on the wrong session is a no-op
+  assert.equal(q.remove('s2', a1), false, 's1 id not found in s2')
+  assert.equal(q.promote('s2', a1), false)
+  assert.deepEqual(q.list('s2').map((x) => x.text), ['s2-a', 's2-b'])
+})
+
+test('clear empties one session and returns the count dropped', () => {
+  const q = createMsgQueue()
+  q.enqueue('s1', 'a')
+  q.enqueue('s1', 'b')
+  q.enqueue('s2', 'c')
+  assert.equal(q.clear('s1'), 2)
+  assert.equal(q.size('s1'), 0)
+  assert.equal(q.size('s2'), 1, 'other session survives a targeted clear')
+  assert.equal(q.clear('unknown'), 0)
+})
+
+test('clearAll wipes every session (crash / profile switch) and totals the drop', () => {
+  const q = createMsgQueue()
+  q.enqueue('s1', 'a')
+  q.enqueue('s1', 'b')
+  q.enqueue('s2', 'c')
+  assert.equal(q.clearAll(), 3)
+  assert.equal(q.size('s1'), 0)
+  assert.equal(q.size('s2'), 0)
+  assert.deepEqual(q.list('s1'), [])
+})
+
+test('list returns copies — mutating the result cannot corrupt the queue', () => {
+  const q = createMsgQueue()
+  q.enqueue('s1', 'a')
+  const snap = q.list('s1')
+  snap[0].text = 'HACKED'
+  snap.push({ id: 999, text: 'injected' })
+  assert.equal(q.list('s1')[0].text, 'a', 'internal item untouched')
+  assert.equal(q.size('s1'), 1, 'internal length untouched')
+})

examples/desktop/test/renderer-collisions.test.js

@@ -143,6 +143,12 @@ const NON_IIFE_ALLOWLIST = new Set([
   'intervention-timeline.js',
   'compact-config-model.js',
   'subagent-drilldown.js',
+  // lane-msg-queue (2026-07-20) composer message queue: dual-exported pure
+  // FIFO model — module.exports for node --test, window.__dshMsgQueueModel
+  // for the renderer. Same shape as compact-config-model.js; preloadPure
+  // require()s it so it must not be IIFE-wrapped. Sole top-level binding is
+  // `function createMsgQueue`, unique across the shared scope.
+  'msg-queue-model.js',
 ])
 
 function listRendererScripts() {

examples/desktop/test/renderer-harness.js

@@ -419,6 +419,7 @@ async function loadRenderer(customStubs = {}, options = {}) {
     ['tool-cards.js', '__dshToolCards'],
     ['widgets.js', '__dshWidgets'],
     ['capabilities.js', '__dshCapabilities'],
+    ['msg-queue-model.js', '__dshMsgQueueModel'],
   ]
   for (const [file, key] of preloadPure) {
     const p = path.join(__dirname, '..', 'src', 'renderer', file)

examples/desktop/test/renderer-msg-queue.test.js

@@ -0,0 +1,196 @@
+// Renderer-level tests for the composer message queue (lane-msg-queue).
+//
+// Covers the wiring the pure msg-queue-model.js tests can't reach:
+//   - send() enqueues instead of sendPrompt when a turn is in flight
+//   - the queue strip renders/hides per the active session's queue
+//   - turn/end auto-drains exactly ONE queued item through sendPrompt
+//   - session.finished drains once too, and doesn't double-drain with turn/end
+//   - per-session isolation: a background session's turn/end never touches
+//     the foreground session's composer
+//   - runtime restart (onInitialized) clears every queue
+//
+// The harness loads the whole renderer against a DOM stub and exposes the
+// send entry point + queue handle via window.__dshRenderer.
+
+'use strict'
+
+const test = require('node:test')
+const assert = require('node:assert/strict')
+const { loadRenderer } = require('./renderer-harness.js')
+
+// Drive an in-flight turn on `sid` and make it active, returning refs.
+async function activeInflight(renderer, document, sid = 's1') {
+  renderer.ensureSession(sid, { title: 'sess', header: {}, hasUserMessage: true })
+  await renderer.selectSession(sid)
+  renderer.onSessionEvent(sid, { type: 'turn/start', seq: 1 })
+  return { input: document.getElementById('input') }
+}
+
+function sendCalls(dsh) {
+  return dsh.__calls.filter((c) => c[0] === 'sendPrompt')
+}
+
+test('send() enqueues instead of sendPrompt while a turn is in flight', async () => {
+  const { renderer, document, dsh } = await loadRenderer()
+  const { input } = await activeInflight(renderer, document)
+  const before = sendCalls(dsh).length
+  input.value = 'queued follow-up'
+  await renderer.send()
+  assert.equal(sendCalls(dsh).length, before, 'no sendPrompt fired mid-turn')
+  assert.deepEqual(renderer.listMsgQueue('s1').map((x) => x.text), ['queued follow-up'])
+  assert.equal(input.value, '', 'composer cleared as if sent')
+})
+
+test('whitespace-only mid-turn input never enqueues', async () => {
+  const { renderer, document } = await loadRenderer()
+  const { input } = await activeInflight(renderer, document)
+  input.value = '   '
+  await renderer.send()
+  assert.equal(renderer.listMsgQueue('s1').length, 0)
+})
+
+test('queue strip renders one chip per queued message + counter, hides when empty', async () => {
+  const { renderer, document } = await loadRenderer()
+  const { input } = await activeInflight(renderer, document)
+  const strip = document.getElementById('msg-queue-strip')
+  assert.equal(strip.hidden, true, 'hidden with an empty queue')
+  input.value = 'first'; await renderer.send()
+  input.value = 'second'; await renderer.send()
+  assert.equal(strip.hidden, false, 'shown once queued')
+  assert.equal(strip.querySelectorAll('.msg-queue-chip').length, 2)
+  const badge = strip.querySelector('.msg-queue-count')
+  assert.match(badge.textContent, /queued 2/)
+})
+
+test('turn/end auto-drains exactly one queued item through sendPrompt', async () => {
+  const { renderer, document, dsh } = await loadRenderer()
+  const { input } = await activeInflight(renderer, document)
+  input.value = 'one'; await renderer.send()
+  input.value = 'two'; await renderer.send()
+  const before = sendCalls(dsh).length
+  renderer.onSessionEvent('s1', { type: 'turn/end', seq: 2 })
+  // drain is async (dispatchPrompt awaits sendPrompt) — let microtasks settle.
+  await new Promise((r) => setTimeout(r, 5))
+  const after = sendCalls(dsh)
+  assert.equal(after.length - before, 1, 'exactly one drained send')
+  assert.equal(after[after.length - 1][2], 'one', 'FIFO: head sent first')
+  assert.deepEqual(renderer.listMsgQueue('s1').map((x) => x.text), ['two'],
+    'the second item waits for its own turn to finish')
+})
+
+test('a second turn/end drains the next item (one per completion)', async () => {
+  const { renderer, document, dsh } = await loadRenderer()
+  const { input } = await activeInflight(renderer, document)
+  input.value = 'one'; await renderer.send()
+  input.value = 'two'; await renderer.send()
+  renderer.onSessionEvent('s1', { type: 'turn/end', seq: 2 })
+  await new Promise((r) => setTimeout(r, 5))
+  // the drained 'one' send flipped inflightTurn back on; simulate its turn.
+  renderer.onSessionEvent('s1', { type: 'turn/start', seq: 3 })
+  renderer.onSessionEvent('s1', { type: 'turn/end', seq: 4 })
+  await new Promise((r) => setTimeout(r, 5))
+  const sent = sendCalls(dsh).map((c) => c[2])
+  assert.deepEqual(sent, ['one', 'two'], 'both drained in FIFO order across two turns')
+  assert.equal(renderer.listMsgQueue('s1').length, 0)
+})
+
+test('turn/end + session.finished for one turn drains only once', async () => {
+  const { renderer, document, dsh, listeners } = await loadRenderer()
+  const { input } = await activeInflight(renderer, document)
+  input.value = 'one'; await renderer.send()
+  input.value = 'two'; await renderer.send()
+  const before = sendCalls(dsh).length
+  // Some daemons emit both boundaries for the same turn.
+  renderer.onSessionEvent('s1', { type: 'turn/end', seq: 2 })
+  await new Promise((r) => setTimeout(r, 5))
+  listeners.onNotify({ method: 'session.finished', params: { sessionId: 's1', status: 'ok' } })
+  await new Promise((r) => setTimeout(r, 5))
+  assert.equal(sendCalls(dsh).length - before, 1, 'drain-once guard held across both signals')
+  assert.deepEqual(renderer.listMsgQueue('s1').map((x) => x.text), ['two'])
+})
+
+test('session.finished alone (no turn/end) still drains once', async () => {
+  const { renderer, document, dsh, listeners } = await loadRenderer()
+  const { input } = await activeInflight(renderer, document)
+  input.value = 'only'; await renderer.send()
+  const before = sendCalls(dsh).length
+  listeners.onNotify({ method: 'session.finished', params: { sessionId: 's1', status: 'error' } })
+  await new Promise((r) => setTimeout(r, 5))
+  assert.equal(sendCalls(dsh).length - before, 1, 'error-path completion drained the head')
+})
+
+test('cancelled turn (turn/end after cancel) still drains — queue survives Cancel', async () => {
+  const { renderer, document, dsh } = await loadRenderer()
+  const { input } = await activeInflight(renderer, document)
+  input.value = 'after cancel'; await renderer.send()
+  // User cancels; the wire still closes the turn with turn/end.
+  const before = sendCalls(dsh).length
+  renderer.onSessionEvent('s1', { type: 'turn/end', seq: 2 })
+  await new Promise((r) => setTimeout(r, 5))
+  assert.equal(sendCalls(dsh).length - before, 1, 'queued follow-up sent on the cancelled turn end')
+})
+
+test('per-session isolation: a background turn/end never touches the active composer', async () => {
+  const { renderer, document, dsh } = await loadRenderer()
+  // s1 active + in flight, one queued item.
+  const { input } = await activeInflight(renderer, document, 's1')
+  input.value = 's1-queued'; await renderer.send()
+  // s2 exists, has its own in-flight turn + queue, but is NOT active.
+  renderer.ensureSession('s2', { title: 's2', header: {}, hasUserMessage: true, running: true })
+  renderer.getMsgQueue().enqueue('s2', 's2-queued')
+  // Arm s2's drain flag via a background turn/start (not the active session,
+  // so it doesn't touch the composer), then end it.
+  renderer.onSessionEvent('s2', { type: 'turn/start', seq: 8 })
+  const before = sendCalls(dsh).length
+  renderer.onSessionEvent('s2', { type: 'turn/end', seq: 9 })
+  await new Promise((r) => setTimeout(r, 5))
+  const sent = sendCalls(dsh).slice(before).map((c) => [c[1], c[2]])
+  assert.deepEqual(sent, [['s2', 's2-queued']], 'only s2 drained, sent against s2')
+  // s1's queue + composer untouched.
+  assert.deepEqual(renderer.listMsgQueue('s1').map((x) => x.text), ['s1-queued'])
+  const strip = document.getElementById('msg-queue-strip')
+  assert.equal(strip.querySelectorAll('.msg-queue-chip').length, 1, 'active strip still shows s1')
+})
+
+test('switching sessions shows the target session\'s queue (strict isolation)', async () => {
+  const { renderer, document } = await loadRenderer()
+  const { input } = await activeInflight(renderer, document, 's1')
+  input.value = 's1-only'; await renderer.send()
+  const strip = document.getElementById('msg-queue-strip')
+  assert.equal(strip.querySelectorAll('.msg-queue-chip').length, 1)
+  // Switch to a fresh idle session — its queue is empty, strip hides.
+  renderer.ensureSession('s2', { title: 's2', header: {}, hasUserMessage: true })
+  await renderer.selectSession('s2')
+  assert.equal(strip.hidden, true, 'empty queue on s2 hides the strip')
+  // Switch back — s1's queue is intact.
+  await renderer.selectSession('s1')
+  assert.equal(strip.querySelectorAll('.msg-queue-chip').length, 1)
+})
+
+test('runtime restart (onInitialized) clears every queue and posts a notice', async () => {
+  const { renderer, document, listeners } = await loadRenderer()
+  const { input } = await activeInflight(renderer, document, 's1')
+  input.value = 'doomed'; await renderer.send()
+  renderer.getMsgQueue().enqueue('s2', 'also doomed')
+  // Fire the initialize handshake (new daemon / profile switch).
+  listeners.onInitialized({ serverInfo: { name: 'echo', version: '1' }, protocolVersion: 1 })
+  await new Promise((r) => setTimeout(r, 5))
+  assert.equal(renderer.getMsgQueue().size('s1'), 0)
+  assert.equal(renderer.getMsgQueue().size('s2'), 0)
+  assert.match(renderer.getStreamText(), /cleared 2 queued messages/)
+})
+
+test('drained send re-arms inflightTurn so a follow-up Enter queues again', async () => {
+  const { renderer, document, dsh } = await loadRenderer()
+  const { input } = await activeInflight(renderer, document)
+  input.value = 'one'; await renderer.send()
+  input.value = 'two'; await renderer.send()
+  renderer.onSessionEvent('s1', { type: 'turn/end', seq: 2 })
+  await new Promise((r) => setTimeout(r, 5))
+  // 'one' is now in flight (dispatchPrompt set inflightTurn). A new Enter
+  // should queue behind 'two', not fire a second concurrent sendPrompt.
+  const before = sendCalls(dsh).length
+  input.value = 'three'; await renderer.send()
+  assert.equal(sendCalls(dsh).length, before, 'follow-up queued, not sent concurrently')
+  assert.deepEqual(renderer.listMsgQueue('s1').map((x) => x.text), ['two', 'three'])
+})