Bump to v2026.10.2

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

USER_GUIDE.md

@@ -70,7 +70,13 @@ send. Use **Shift+Enter** to add a line break without sending.
 
 ## Formatting
 
-Messages support Markdown:
+Messages support Markdown. Prefer buttons to typing the syntax? Click the
+**Aa** button next to the emoji button in the composer to open a formatting
+toolbar — it inserts the markdown below into your message for you (select some
+text first to wrap it, or click a button again to take the formatting back
+off). It stays collapsed until you open it, and remembers your choice.
+
+Or type it yourself:
 
 - `**bold**`, `*italic*`, `~~strikethrough~~`
 - `` `inline code` `` and fenced code blocks (three backticks)

backend/app/main.py

@@ -58,8 +58,12 @@ async def lifespan(app: FastAPI) -> AsyncIterator[None]:
     # ASGITransport, used by the plain REST test fixtures -- only
     # TestClient's websocket_connect-based tests actually run lifespan).
     # The background listener task genuinely needs a running event loop
-    # though, so that part stays here.
+    # though, so that part stays here. run_forever() (not listen() directly)
-    listener_task = asyncio.create_task(app.state.broadcaster.listen())
+    # -- #76: a bare listen() here died permanently and silently the moment
+    # its Redis connection ever dropped (e.g. Redis itself restarting),
+    # with nothing to notice or reconnect; run_forever() supervises it and
+    # restarts on failure instead.
+    listener_task = asyncio.create_task(app.state.broadcaster.run_forever())
 
     yield
 

backend/app/ws/broadcaster.py

@@ -1,13 +1,26 @@
+import asyncio
+import contextlib
 import json
+import logging
 import uuid
 
 from redis.asyncio import Redis
 
 from app.ws.connection_manager import ConnectionManager
 
+logger = logging.getLogger(__name__)
+
 ROOM_CHANNEL_PREFIX = "room:"
 USER_CHANNEL_PREFIX = "user:"
 
+# #76: a run shorter than this before dying doesn't count as "stable" for
+# resetting the backoff in run_forever() below -- long enough that a real,
+# working connection has clearly settled in, short enough not to leave a
+# just-recovered listener exposed to a full backoff climb if Redis blips
+# again shortly after reconnecting.
+STABLE_RUN_SECONDS = 60
+MAX_BACKOFF_SECONDS = 30
+
 
 class Broadcaster:
     """Cross-instance message fan-out (ARCHITECTURE.md phase 5).
@@ -36,6 +49,43 @@ class Broadcaster:
     async def publish_to_user(self, user_id: uuid.UUID, payload: dict) -> None:
         await self._redis.publish(f"{USER_CHANNEL_PREFIX}{user_id}", json.dumps(payload))
 
+    async def run_forever(self) -> None:
+        """Supervises listen(), restarting it if it ever dies.
+
+        #76's real root cause, found after the per-message try/except below
+        turned out not to be enough: this is the *one* pubsub listener for
+        the whole process (see main.py's lifespan), created once at startup
+        with nothing watching over it afterward. A connection-level failure
+        -- Redis restarting, a network blip between the app and Redis --
+        raises from the `async for` iteration in listen() itself, outside
+        that per-message guard, and previously killed this task permanently
+        and silently: HTTP/REST and login kept working fine (neither
+        touches this), but live message delivery was gone for every room
+        and every user on this instance until the whole process was
+        restarted. Confirmed live in production: Redis got restarted by an
+        OS update, and `PUBSUB NUMPAT` against it afterward showed zero
+        pattern subscriptions across all 4 gunicorn workers -- every one of
+        them had silently lost its listener with nothing to bring it back.
+        """
+        backoff_seconds = 1.0
+        while True:
+            started_at = asyncio.get_event_loop().time()
+            try:
+                await self.listen()
+                logger.warning("Broadcaster.listen() exited without error -- restarting")
+            except asyncio.CancelledError:
+                raise
+            except Exception:
+                logger.error("Broadcaster.listen() failed -- restarting", exc_info=True)
+            ran_for = asyncio.get_event_loop().time() - started_at
+            # Sleep at the *current* backoff first, then grow it for next
+            # time -- computing the next value before sleeping would skip
+            # straight past the first (shortest) retry delay.
+            await asyncio.sleep(backoff_seconds)
+            backoff_seconds = (
+                1.0 if ran_for > STABLE_RUN_SECONDS else min(backoff_seconds * 2, MAX_BACKOFF_SECONDS)
+            )
+
     async def listen(self) -> None:
         pubsub = self._redis.pubsub()
         await pubsub.psubscribe(f"{ROOM_CHANNEL_PREFIX}*", f"{USER_CHANNEL_PREFIX}*")
@@ -43,14 +93,37 @@ class Broadcaster:
             async for message in pubsub.listen():
                 if message["type"] != "pmessage":
                     continue
-                channel = message["channel"]
+                # #76: this is the one pubsub listener for the whole process
-                payload = json.loads(message["data"])
+                # (see main.py's lifespan) -- ConnectionManager.broadcast/
-                if channel.startswith(ROOM_CHANNEL_PREFIX):
+                # send_to_user already guard against one dead socket taking
-                    room_id = uuid.UUID(channel.removeprefix(ROOM_CHANNEL_PREFIX))
+                # the rest of a single fan-out down, but this belt-and-
-                    await self._manager.broadcast(room_id, payload)
+                # suspenders catch is for anything else unexpected (a
-                elif channel.startswith(USER_CHANNEL_PREFIX):
+                # malformed payload, e.g.) doing the same. An uncaught
-                    user_id = uuid.UUID(channel.removeprefix(USER_CHANNEL_PREFIX))
+                # exception here previously meant *this whole async for*
-                    await self._manager.send_to_user(user_id, payload)
+                # loop died silently -- no more live delivery to any room on
+                # this instance, for anyone, until the process restarted.
+                try:
+                    channel = message["channel"]
+                    payload = json.loads(message["data"])
+                    if channel.startswith(ROOM_CHANNEL_PREFIX):
+                        room_id = uuid.UUID(channel.removeprefix(ROOM_CHANNEL_PREFIX))
+                        await self._manager.broadcast(room_id, payload)
+                    elif channel.startswith(USER_CHANNEL_PREFIX):
+                        user_id = uuid.UUID(channel.removeprefix(USER_CHANNEL_PREFIX))
+                        await self._manager.send_to_user(user_id, payload)
+                except Exception:
+                    logger.error("Error handling pubsub message on channel %s", message.get("channel"), exc_info=True)
         finally:
-            await pubsub.punsubscribe(f"{ROOM_CHANNEL_PREFIX}*", f"{USER_CHANNEL_PREFIX}*")
+            # #76: reached via a connection that's already dead just as
-            await pubsub.aclose()
+            # often as a clean shutdown (that's the whole failure mode
+            # run_forever() now recovers from) -- punsubscribe/aclose over
+            # a broken connection would themselves raise, masking whatever
+            # actually killed the loop above and, since run_forever() only
+            # starts backing off *after* listen() returns/raises, delaying
+            # the reconnect for no benefit (a fresh pubsub object is about
+            # to be created on retry regardless of whether this cleanup
+            # succeeded).
+            with contextlib.suppress(Exception):
+                await pubsub.punsubscribe(f"{ROOM_CHANNEL_PREFIX}*", f"{USER_CHANNEL_PREFIX}*")
+            with contextlib.suppress(Exception):
+                await pubsub.aclose()

backend/app/ws/chat.py

@@ -1,3 +1,4 @@
+import asyncio
 import uuid
 
 from fastapi import APIRouter, Depends, WebSocket, WebSocketDisconnect
@@ -31,6 +32,18 @@ router = APIRouter(tags=["ws"])
 
 WS_UNAUTHENTICATED = 4401
 
+# #76: comfortably under the ~60s idle-connection timeout common to reverse
+# proxies/load balancers sitting in front of this endpoint, and short enough
+# that the frontend's own zombie-detection watchdog (useChatSocket.ts) can
+# notice a dead connection and reconnect well within a session -- a socket
+# can go silently dead (no close frame at all, e.g. a laptop sleeping or a
+# NAT dropping an idle mapping) without this, and no live message reaches it
+# again until *something* else finally triggers a close, which used to be
+# "switch rooms and back" purely by accident (that remounts the message
+# list, which refetches history over plain REST -- unrelated to the socket
+# itself actually recovering).
+WS_PING_INTERVAL_SECONDS = 30
+
 
 class ClientEnvelope(BaseModel):
     type: str
@@ -124,7 +137,18 @@ async def chat_endpoint(websocket: WebSocket, db: AsyncSession = Depends(get_db)
 
     try:
         while True:
-            raw = await websocket.receive_json()
+            try:
+                raw = await asyncio.wait_for(
+                    websocket.receive_json(), timeout=WS_PING_INTERVAL_SECONDS
+                )
+            except asyncio.TimeoutError:
+                # Nothing received in a while -- ping rather than assume the
+                # connection's still good. A genuinely dead socket fails this
+                # send (raising, caught below same as any other disconnect);
+                # a merely quiet one just gets proded and the loop continues
+                # waiting.
+                await websocket.send_json({"type": "ping"})
+                continue
             try:
                 try:
                     envelope = ClientEnvelope.model_validate(raw)
@@ -146,6 +170,14 @@ async def chat_endpoint(websocket: WebSocket, db: AsyncSession = Depends(get_db)
                     joined_rooms.add(envelope.room_id)
                     await websocket.send_json({"type": "joined", "room_id": str(envelope.room_id)})
 
+                elif envelope.type == "pong":
+                    # #76: the client's reply to our "ping" above -- nothing
+                    # to do with it. Its only purpose is resetting the
+                    # frontend's own liveness watchdog; the timeout on the
+                    # receive_json() above already gets reset by receiving
+                    # any frame at all, this one included.
+                    pass
+
                 elif envelope.type == "leave":
                     if envelope.room_id is None:
                         await websocket.send_json({"type": "error", "detail": "room_id required"})

backend/app/ws/connection_manager.py

@@ -1,8 +1,11 @@
+import logging
 import uuid
 from collections import defaultdict
 
 from fastapi import WebSocket
 
+logger = logging.getLogger(__name__)
+
 
 class ConnectionManager:
     """Local, single-process WebSocket socket registry.
@@ -43,8 +46,22 @@ class ConnectionManager:
 
     async def broadcast(self, room_id: uuid.UUID, payload: dict) -> None:
         for websocket in list(self._rooms.get(room_id, ())):
-            await websocket.send_json(payload)
+            # #76: one dead/racing socket (e.g. its own disconnect cleanup
+            # hasn't finished removing it from _rooms yet) must not take the
+            # rest of this broadcast down with it -- this runs inside
+            # Broadcaster.listen()'s single, never-restarted per-process
+            # pubsub loop, so an unhandled exception here previously meant
+            # one bad socket silently killed *live delivery for every room
+            # on this instance*, not just the one socket, until the process
+            # was restarted.
+            try:
+                await websocket.send_json(payload)
+            except Exception:
+                logger.warning("Dropping dead socket during broadcast to room %s", room_id, exc_info=True)
 
     async def send_to_user(self, user_id: uuid.UUID, payload: dict) -> None:
         for websocket in list(self._users.get(user_id, ())):
-            await websocket.send_json(payload)
+            try:
+                await websocket.send_json(payload)
+            except Exception:
+                logger.warning("Dropping dead socket sending to user %s", user_id, exc_info=True)

backend/pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "ds-chat"
-version = "2026.9.4"
+version = "2026.10.2"
 description = "DS Chat backend service"
 license = { text = "AGPL-3.0-or-later" }
 requires-python = ">=3.11"

backend/tests/test_broadcaster_supervision.py

@@ -0,0 +1,61 @@
+import asyncio
+
+import pytest
+
+from app.ws.broadcaster import Broadcaster
+
+
+async def test_run_forever_restarts_after_listen_raises(monkeypatch):
+    # #76: listen() dying (a dropped Redis connection, most commonly -- e.g.
+    # Redis itself restarting) must not permanently kill live delivery for
+    # the whole process. run_forever() has to notice and restart it, not
+    # just let the background task disappear silently while everything else
+    # (login, REST endpoints) keeps working fine.
+    broadcaster = Broadcaster(redis=None, manager=None)
+    calls = 0
+
+    async def fake_listen():
+        nonlocal calls
+        calls += 1
+        if calls < 3:
+            raise ConnectionError("redis went away")
+        # Stop the loop once the retry behavior below is proven, rather
+        # than looping forever in a test.
+        raise asyncio.CancelledError()
+
+    monkeypatch.setattr(broadcaster, "listen", fake_listen)
+    sleep_calls = []
+
+    async def fake_sleep(seconds):
+        sleep_calls.append(seconds)
+
+    monkeypatch.setattr(asyncio, "sleep", fake_sleep)
+
+    with pytest.raises(asyncio.CancelledError):
+        await broadcaster.run_forever()
+
+    assert calls == 3
+    # Slept once after each of the first two failures (exponential:
+    # 1s, then 2s) -- not after the third, which is the CancelledError
+    # that stops the loop before reaching the sleep.
+    assert sleep_calls == [1.0, 2.0]
+
+
+async def test_run_forever_does_not_swallow_cancellation(monkeypatch):
+    # A genuine shutdown (the app's own lifespan cancels this task) must
+    # propagate immediately, not get treated as just another failure to
+    # retry after a backoff.
+    broadcaster = Broadcaster(redis=None, manager=None)
+
+    async def fake_listen():
+        raise asyncio.CancelledError()
+
+    monkeypatch.setattr(broadcaster, "listen", fake_listen)
+
+    async def fail_if_called(seconds):
+        raise AssertionError("should not sleep/retry on cancellation")
+
+    monkeypatch.setattr(asyncio, "sleep", fail_if_called)
+
+    with pytest.raises(asyncio.CancelledError):
+        await broadcaster.run_forever()

backend/tests/test_ws_chat.py

@@ -109,6 +109,24 @@ def test_history_tiebreaks_identical_timestamps_by_id(ws_client):
     assert [m["content"] for m in history] == [m["content"] for m in expected_order]
 
 
+def test_ws_sends_heartbeat_ping(ws_client, monkeypatch):
+    # #76: with nothing else sent on the connection, a "ping" must arrive
+    # proactively once the idle timeout elapses -- shrunk here so the test
+    # doesn't actually wait the real 30s. Replying "pong" (the frontend's
+    # own behavior) must be accepted silently and leave the connection
+    # fully usable afterward, not treated as an unknown message type.
+    monkeypatch.setattr("app.ws.chat.WS_PING_INTERVAL_SECONDS", 0.05)
+    username = _unique("alice")
+    _register(ws_client, username=username)
+    room = ws_client.post("/api/rooms", json={"name": _unique("general")}).json()
+
+    with ws_client.websocket_connect("/ws/chat") as ws:
+        assert ws.receive_json() == {"type": "ping"}
+        ws.send_json({"type": "pong"})
+        ws.send_json({"type": "join", "room_id": room["id"]})
+        assert ws.receive_json() == {"type": "joined", "room_id": room["id"]}
+
+
 def test_ws_message_without_join_errors(ws_client):
     _register(ws_client, username=_unique("alice"))
     room = ws_client.post("/api/rooms", json={"name": _unique("general")}).json()

frontend/package.json

@@ -1,14 +1,15 @@
 {
   "name": "frontend",
   "private": true,
-  "version": "2026.9.4",
+  "version": "2026.10.2",
   "license": "AGPL-3.0-or-later",
   "type": "module",
   "scripts": {
     "dev": "vite",
     "build": "tsc -b && vite build",
     "lint": "oxlint",
-    "preview": "vite preview"
+    "preview": "vite preview",
+    "test": "vitest run"
   },
   "dependencies": {
     "markdown-to-jsx": "^9.10.2",
@@ -18,13 +19,16 @@
     "vite-plugin-pwa": "^1.3.0"
   },
   "devDependencies": {
+    "@testing-library/react": "^16.3.3",
     "@types/node": "^24.13.3",
     "@types/react": "^19.2.17",
     "@types/react-dom": "^19.2.3",
     "@vitejs/plugin-react": "^6.0.4",
+    "jsdom": "^30.1.1",
     "oxlint": "^1.75.0",
     "typescript": "~6.0.2",
     "vite": "^8.2.0",
+    "vitest": "^5.0.2",
     "workbox-cacheable-response": "^7.4.1",
     "workbox-expiration": "^7.4.1",
     "workbox-precaching": "^7.4.1",

frontend/src/components/Composer.css

@@ -105,6 +105,34 @@
   cursor: not-allowed;
 }
 
+.composer-format-toggle {
+  width: 36px;
+  height: 36px;
+  flex: none;
+  border-radius: var(--radius);
+  background: transparent;
+  color: var(--ds-muted);
+  border: 1px solid var(--ds-border);
+  font-size: 0.82rem;
+  font-weight: 700;
+  line-height: 1;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  cursor: pointer;
+}
+
+.composer-format-toggle:hover:not(:disabled),
+.composer-format-toggle-open {
+  color: var(--ds-text);
+  border-color: var(--ds-accent);
+}
+
+.composer-format-toggle:disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+}
+
 .composer-attach-wrap {
   position: relative;
   flex: none;

frontend/src/components/Composer.tsx

@@ -15,10 +15,13 @@ import { getUploadLimit } from '../api/uploads'
 import { useCustomEmoji } from '../context/CustomEmojiContext'
 import { EMOJI_SHORTCODES, SHORTCODE_BY_GLYPH } from '../lib/emojiShortcodes'
 import { formatFileSize } from '../lib/fileSize'
+import { getFormattingToolbarOpen, setFormattingToolbarOpen } from '../lib/formattingToolbarPref'
+import { applyFormat, type FormatAction } from '../lib/markdownFormat'
 import { getRecentEmoji, recordEmojiUsed } from '../lib/recentEmoji'
 import type { MyRoomItem, RoomMember } from '../types'
 import { EmojiPicker } from './EmojiPicker'
 import { EmojiShortcodeAutocomplete, type EmojiShortcodeMatch } from './EmojiShortcodeAutocomplete'
+import { FormattingToolbar } from './FormattingToolbar'
 import { MentionAutocomplete } from './MentionAutocomplete'
 import { RoomReferenceAutocomplete } from './RoomReferenceAutocomplete'
 import './Composer.css'
@@ -136,6 +139,7 @@ export function Composer({ roomId, roomName, isDm, members, rooms, disabled, arc
   const [emojiActiveIndex, setEmojiActiveIndex] = useState(0)
   const [dragActive, setDragActive] = useState(false)
   const [attachMenuOpen, setAttachMenuOpen] = useState(false)
+  const [toolbarOpen, setToolbarOpen] = useState(getFormattingToolbarOpen)
   const { byShortcode: customEmojiByShortcode } = useCustomEmoji()
   const textareaRef = useRef<HTMLTextAreaElement>(null)
   const fileInputRef = useRef<HTMLInputElement>(null)
@@ -449,6 +453,29 @@ export function Composer({ roomId, roomName, isDm, members, rooms, disabled, arc
     })
   }
 
+  function toggleToolbar() {
+    const next = !toolbarOpen
+    setToolbarOpen(next)
+    setFormattingToolbarOpen(next)
+  }
+
+  // #75: the toolbar only ever edits the textarea's plain markdown text --
+  // nothing about what gets sent changes.
+  function applyFormatAction(action: FormatAction) {
+    const el = textareaRef.current
+    if (!el) return
+    const result = applyFormat(
+      { value, start: el.selectionStart ?? value.length, end: el.selectionEnd ?? value.length },
+      action,
+    )
+    setValue(result.value)
+    requestAnimationFrame(() => {
+      el.focus()
+      el.setSelectionRange(result.start, result.end)
+      autoGrow()
+    })
+  }
+
   function insertEmoji(emoji: string) {
     const el = textareaRef.current
     setEmojiPickerOpen(false)
@@ -517,6 +544,9 @@ export function Composer({ roomId, roomName, isDm, members, rooms, disabled, arc
         </div>
       )}
       {uploadError && <div className="composer-status composer-error">{uploadError}</div>}
+      {toolbarOpen && (
+        <FormattingToolbar id="composer-formatting-toolbar" disabled={isDisabled} onAction={applyFormatAction} />
+      )}
       <div className="composer-box">
         <input
           ref={photoInputRef}
@@ -589,6 +619,18 @@ export function Composer({ roomId, roomName, isDm, members, rooms, disabled, arc
             />
           )}
         </div>
+        <button
+          type="button"
+          className={`composer-format-toggle${toolbarOpen ? ' composer-format-toggle-open' : ''}`}
+          onClick={toggleToolbar}
+          disabled={isDisabled}
+          aria-label="Formatting options"
+          aria-expanded={toolbarOpen}
+          aria-controls="composer-formatting-toolbar"
+          title="Formatting options"
+        >
+          Aa
+        </button>
         <div className="composer-textarea-wrap">
           <textarea
             ref={textareaRef}

frontend/src/components/FormattingToolbar.css

@@ -0,0 +1,41 @@
+.formatting-toolbar {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: center;
+  /* Spacing, not divider lines, between groups -- a border on every group
+     after the first leaves a dangling line at the start of the second row
+     whenever the toolbar wraps on a narrow screen. */
+  gap: 2px 14px;
+}
+
+.formatting-toolbar-group {
+  display: flex;
+  gap: 2px;
+}
+
+.formatting-toolbar-btn {
+  min-width: 30px;
+  height: 30px;
+  padding: 0 6px;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  background: transparent;
+  border: none;
+  border-radius: 6px;
+  color: var(--ds-muted);
+  font-size: 0.82rem;
+  line-height: 1;
+  text-decoration: none;
+  cursor: pointer;
+}
+
+.formatting-toolbar-btn:hover:not(:disabled) {
+  background: var(--ds-surface-2);
+  color: var(--ds-text);
+}
+
+.formatting-toolbar-btn:disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+}

frontend/src/components/FormattingToolbar.test.tsx

@@ -0,0 +1,55 @@
+import { cleanup, fireEvent, render, screen } from '@testing-library/react'
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import type { FormatAction } from '../lib/markdownFormat'
+import { FormattingToolbar } from './FormattingToolbar'
+
+afterEach(cleanup)
+
+const EXPECTED: [string, FormatAction][] = [
+  ['Bold', { kind: 'inline', marker: '**' }],
+  ['Italic', { kind: 'inline', marker: '*' }],
+  ['Strikethrough', { kind: 'inline', marker: '~~' }],
+  ['Inline code', { kind: 'inline', marker: '`' }],
+  ['Code block', { kind: 'codeBlock' }],
+  ['Link', { kind: 'link' }],
+  ['Quote', { kind: 'prefix', prefix: 'quote' }],
+  ['Bulleted list', { kind: 'prefix', prefix: 'bullet' }],
+  ['Numbered list', { kind: 'prefix', prefix: 'ordered' }],
+  ['Heading 1', { kind: 'heading', level: 1 }],
+  ['Heading 2', { kind: 'heading', level: 2 }],
+  ['Heading 3', { kind: 'heading', level: 3 }],
+  ['Subscript', { kind: 'inline', marker: '~' }],
+  ['Superscript', { kind: 'inline', marker: '^' }],
+]
+
+describe('FormattingToolbar', () => {
+  it.each(EXPECTED)('%s button calls onAction with its action', (label, action) => {
+    const onAction = vi.fn()
+    render(<FormattingToolbar id="t" onAction={onAction} />)
+    fireEvent.click(screen.getByRole('button', { name: label }))
+    expect(onAction).toHaveBeenCalledTimes(1)
+    expect(onAction).toHaveBeenCalledWith(action)
+  })
+
+  it('disables every button when disabled, but leaves the help link usable', () => {
+    render(<FormattingToolbar id="t" disabled onAction={vi.fn()} />)
+    const buttons = screen.getAllByRole('button') as HTMLButtonElement[]
+    expect(buttons).toHaveLength(EXPECTED.length)
+    expect(buttons.every((b) => b.disabled)).toBe(true)
+    expect(screen.getByRole('link', { name: 'Formatting help' })).toBeTruthy()
+  })
+
+  it('opens help in a new tab so the draft in the composer is not lost', () => {
+    render(<FormattingToolbar id="t" onAction={vi.fn()} />)
+    const help = screen.getByRole('link', { name: 'Formatting help' })
+    expect(help.getAttribute('href')).toBe('/help#formatting')
+    expect(help.getAttribute('target')).toBe('_blank')
+    expect(help.getAttribute('rel')).toContain('noopener')
+  })
+
+  it('keeps focus in the textarea by cancelling mousedown on buttons', () => {
+    render(<FormattingToolbar id="t" onAction={vi.fn()} />)
+    // fireEvent returns false when the event's default was prevented.
+    expect(fireEvent.mouseDown(screen.getByRole('button', { name: 'Bold' }))).toBe(false)
+  })
+})

frontend/src/components/FormattingToolbar.tsx

@@ -0,0 +1,104 @@
+import type { ReactNode } from 'react'
+import type { FormatAction, InlineMarker } from '../lib/markdownFormat'
+import './FormattingToolbar.css'
+
+interface FormattingToolbarProps {
+  id: string
+  disabled?: boolean
+  onAction: (action: FormatAction) => void
+}
+
+interface ToolbarButton {
+  label: string
+  // Shows the syntax the button inserts -- the toolbar doubles as the
+  // "quick guide" for people who'd rather learn to type it themselves.
+  title: string
+  content: ReactNode
+  action: FormatAction
+}
+
+const inline = (marker: InlineMarker): FormatAction => ({ kind: 'inline', marker })
+
+const GROUPS: ToolbarButton[][] = [
+  [
+    { label: 'Bold', title: 'Bold: **text**', content: <b>B</b>, action: inline('**') },
+    { label: 'Italic', title: 'Italic: *text*', content: <i>I</i>, action: inline('*') },
+    { label: 'Strikethrough', title: 'Strikethrough: ~~text~~', content: <s>S</s>, action: inline('~~') },
+  ],
+  [
+    { label: 'Inline code', title: 'Inline code: `code`', content: '</>', action: inline('`') },
+    { label: 'Code block', title: 'Code block: ``` on its own lines', content: '{ }', action: { kind: 'codeBlock' } },
+  ],
+  [
+    {
+      label: 'Link',
+      title: 'Link: [text](url)',
+      content: (
+        <svg width="15" height="15" viewBox="0 0 20 20" fill="none" aria-hidden="true">
+          <path
+            d="M8.5 11.5a3 3 0 0 0 4.2 0l2.6-2.6a3 3 0 0 0-4.2-4.2l-.9.9M11.5 8.5a3 3 0 0 0-4.2 0l-2.6 2.6a3 3 0 0 0 4.2 4.2l.9-.9"
+            stroke="currentColor"
+            strokeWidth="1.6"
+            strokeLinecap="round"
+            strokeLinejoin="round"
+          />
+        </svg>
+      ),
+      action: { kind: 'link' },
+    },
+    { label: 'Quote', title: 'Quote: > text', content: '“', action: { kind: 'prefix', prefix: 'quote' } },
+  ],
+  [
+    { label: 'Bulleted list', title: 'Bulleted list: - item', content: '•', action: { kind: 'prefix', prefix: 'bullet' } },
+    { label: 'Numbered list', title: 'Numbered list: 1. item', content: '1.', action: { kind: 'prefix', prefix: 'ordered' } },
+  ],
+  [
+    { label: 'Heading 1', title: 'Heading 1: # text', content: 'H1', action: { kind: 'heading', level: 1 } },
+    { label: 'Heading 2', title: 'Heading 2: ## text', content: 'H2', action: { kind: 'heading', level: 2 } },
+    { label: 'Heading 3', title: 'Heading 3: ### text', content: 'H3', action: { kind: 'heading', level: 3 } },
+  ],
+  [
+    { label: 'Subscript', title: 'Subscript: ~text~ (no spaces)', content: 'x₂', action: inline('~') },
+    { label: 'Superscript', title: 'Superscript: ^text^ (no spaces)', content: 'x²', action: inline('^') },
+  ],
+]
+
+export function FormattingToolbar({ id, disabled, onAction }: FormattingToolbarProps) {
+  return (
+    <div id={id} className="formatting-toolbar" role="toolbar" aria-label="Formatting">
+      {GROUPS.map((group) => (
+        <div key={group[0].label} className="formatting-toolbar-group">
+          {group.map((button) => (
+            <button
+              key={button.label}
+              type="button"
+              className="formatting-toolbar-btn"
+              title={button.title}
+              aria-label={button.label}
+              disabled={disabled}
+              // Keeps focus (and the selection) in the textarea -- a click
+              // on a button would otherwise blur it, and on mobile dismiss
+              // the keyboard.
+              onMouseDown={(e) => e.preventDefault()}
+              onClick={() => onAction(button.action)}
+            >
+              {button.content}
+            </button>
+          ))}
+        </div>
+      ))}
+      {/* A new tab on purpose: the draft lives in Composer's own state, so
+          navigating this one away would lose it. */}
+      <a
+        className="formatting-toolbar-btn formatting-toolbar-help"
+        href="/help#formatting"
+        target="_blank"
+        rel="noopener noreferrer"
+        title="Formatting help (opens in a new tab)"
+        aria-label="Formatting help"
+      >
+        ?
+      </a>
+    </div>
+  )
+}

frontend/src/hooks/useDesktopRoomBridge.test.ts

@@ -0,0 +1,68 @@
+import { renderHook } from '@testing-library/react'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import * as desktopBridge from '../lib/desktopBridge'
+import { useDesktopRoomBridge } from './useDesktopRoomBridge'
+
+describe('useDesktopRoomBridge', () => {
+  beforeEach(() => {
+    vi.spyOn(desktopBridge, 'notifyRoomOpened')
+    vi.spyOn(desktopBridge, 'notifyUnreadCount')
+  })
+
+  afterEach(() => {
+    vi.restoreAllMocks()
+  })
+
+  it('calls roomOpened once when entering a room', () => {
+    renderHook(({ roomId, count }) => useDesktopRoomBridge(roomId, count), {
+      initialProps: { roomId: 'room-1', count: 0 },
+    })
+    expect(desktopBridge.notifyRoomOpened).toHaveBeenCalledTimes(1)
+  })
+
+  it('does not call roomOpened again on a rerender with the same roomId', () => {
+    const { rerender } = renderHook(({ roomId, count }) => useDesktopRoomBridge(roomId, count), {
+      initialProps: { roomId: 'room-1', count: 0 },
+    })
+    expect(desktopBridge.notifyRoomOpened).toHaveBeenCalledTimes(1)
+
+    // Unrelated rerender -- unreadRoomCount changed, roomId did not.
+    rerender({ roomId: 'room-1', count: 3 })
+    rerender({ roomId: 'room-1', count: 3 })
+    expect(desktopBridge.notifyRoomOpened).toHaveBeenCalledTimes(1)
+  })
+
+  it('calls roomOpened again on a genuine transition to a different room', () => {
+    const { rerender } = renderHook(({ roomId, count }) => useDesktopRoomBridge(roomId, count), {
+      initialProps: { roomId: 'room-1', count: 0 },
+    })
+    rerender({ roomId: 'room-2', count: 0 })
+    expect(desktopBridge.notifyRoomOpened).toHaveBeenCalledTimes(2)
+  })
+
+  it('does not call roomOpened when there is no room id', () => {
+    renderHook(({ roomId, count }) => useDesktopRoomBridge(roomId, count), {
+      initialProps: { roomId: undefined as string | undefined, count: 0 },
+    })
+    expect(desktopBridge.notifyRoomOpened).not.toHaveBeenCalled()
+  })
+
+  it('sends the unread count whenever it changes, independent of roomOpened', () => {
+    const { rerender } = renderHook(({ roomId, count }) => useDesktopRoomBridge(roomId, count), {
+      initialProps: { roomId: undefined as string | undefined, count: 0 },
+    })
+    expect(desktopBridge.notifyUnreadCount).toHaveBeenCalledWith(0)
+
+    rerender({ roomId: undefined, count: 2 })
+    expect(desktopBridge.notifyUnreadCount).toHaveBeenCalledWith(2)
+    expect(desktopBridge.notifyRoomOpened).not.toHaveBeenCalled()
+  })
+})
+
+describe('desktop bridge functions with no window.dsDesktop', () => {
+  it('remain optional -- calling them does not throw when the bridge is absent', () => {
+    expect(window.dsDesktop).toBeUndefined()
+    expect(() => desktopBridge.notifyRoomOpened()).not.toThrow()
+    expect(() => desktopBridge.notifyUnreadCount(5)).not.toThrow()
+  })
+})

frontend/src/hooks/useDesktopRoomBridge.ts

@@ -0,0 +1,26 @@
+import { useEffect } from 'react'
+import { notifyRoomOpened, notifyUnreadCount } from '../lib/desktopBridge'
+
+// Tells the Electron desktop wrapper (a) when the user has genuinely
+// entered a room, so it can clear that room's tray indicator, and (b) the
+// current unread-room count, so the tray badge stays accurate. Both are
+// no-ops in every browser build (see desktopBridge.ts).
+//
+// roomOpened must fire only on a genuine transition to a real room id --
+// never merely because the window was shown, focused, restored, or opened
+// from the tray, and never when no room is open at all. Depending on just
+// the id (a primitive, not the room object) is what makes this safe to
+// call from a component that rerenders often: an unrelated rerender that
+// leaves activeRoomId unchanged doesn't rerun the effect, so there's no
+// separate de-duplication to get wrong here -- it falls out of React's own
+// effect-dependency comparison.
+export function useDesktopRoomBridge(activeRoomId: string | undefined, unreadRoomCount: number): void {
+  useEffect(() => {
+    if (!activeRoomId) return
+    notifyRoomOpened()
+  }, [activeRoomId])
+
+  useEffect(() => {
+    notifyUnreadCount(unreadRoomCount)
+  }, [unreadRoomCount])
+}

frontend/src/lib/desktopBridge.ts

@@ -15,6 +15,12 @@ declare global {
   interface Window {
     dsDesktop?: {
       setUnreadCount?(unreadRoomCount: number): void
+      // Tells the tray/dock icon the user has genuinely entered a room --
+      // the desktop wrapper's own signal to clear that room's tray
+      // indicator. Deliberately not fired just because the window was
+      // shown/focused/restored, or opened from the tray: none of those mean
+      // the user actually looked at the room the unread message is in.
+      roomOpened?(): void
       showNotification?(notification: DesktopNotificationRequest): void
       onNotificationClick?(callback: (roomId: string) => void): () => void
     }
@@ -38,6 +44,16 @@ export function isDesktopClickListenerSupported(): boolean {
   return typeof window.dsDesktop?.onNotificationClick === 'function'
 }
 
+// Both no-op silently if the bridge or this specific method isn't present,
+// same as showDesktopNotification below -- callers never need to guard.
+export function notifyRoomOpened(): void {
+  window.dsDesktop?.roomOpened?.()
+}
+
+export function notifyUnreadCount(unreadRoomCount: number): void {
+  window.dsDesktop?.setUnreadCount?.(unreadRoomCount)
+}
+
 // No-ops silently if the bridge or this specific method isn't present --
 // callers don't need to guard, matching the rest of this module's
 // capability-detect-per-method philosophy (see #49's "feature-test each

frontend/src/lib/formattingToolbarPref.test.ts

@@ -0,0 +1,31 @@
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { getFormattingToolbarOpen, setFormattingToolbarOpen } from './formattingToolbarPref'
+
+afterEach(() => {
+  localStorage.clear()
+  vi.restoreAllMocks()
+})
+
+describe('formatting toolbar preference', () => {
+  it('is collapsed by default', () => {
+    expect(getFormattingToolbarOpen()).toBe(false)
+  })
+
+  it('remembers being opened and closed', () => {
+    setFormattingToolbarOpen(true)
+    expect(getFormattingToolbarOpen()).toBe(true)
+    setFormattingToolbarOpen(false)
+    expect(getFormattingToolbarOpen()).toBe(false)
+  })
+
+  it('falls back to collapsed when storage is unavailable', () => {
+    vi.spyOn(Storage.prototype, 'getItem').mockImplementation(() => {
+      throw new Error('blocked')
+    })
+    vi.spyOn(Storage.prototype, 'setItem').mockImplementation(() => {
+      throw new Error('blocked')
+    })
+    expect(getFormattingToolbarOpen()).toBe(false)
+    expect(() => setFormattingToolbarOpen(true)).not.toThrow()
+  })
+})

frontend/src/lib/formattingToolbarPref.ts

@@ -0,0 +1,21 @@
+const KEY = 'ds-chat-formatting-toolbar-open'
+
+// Collapsed unless the user has opened it before -- and remembered, because
+// Composer remounts on every room switch and would otherwise snap shut each
+// time.
+export function getFormattingToolbarOpen(): boolean {
+  try {
+    return localStorage.getItem(KEY) === 'true'
+  } catch {
+    return false
+  }
+}
+
+export function setFormattingToolbarOpen(open: boolean): void {
+  try {
+    localStorage.setItem(KEY, String(open))
+  } catch {
+    // storage unavailable (private browsing, quota) -- the toolbar just
+    // won't remember its state, not fatal.
+  }
+}

frontend/src/lib/markdownFormat.test.ts

@@ -0,0 +1,139 @@
+import { describe, expect, it } from 'vitest'
+import { applyFormat, type FormatAction, type InlineMarker, type TextState } from './markdownFormat'
+
+// ⟦ and ⟧ mark the selection, so cases read as plain strings -- an empty
+// pair (⟦⟧) is a bare cursor.
+const L = '⟦'
+const R = '⟧'
+
+function parse(s: string): TextState {
+  const start = s.indexOf(L)
+  const end = s.indexOf(R) - 1
+  return { value: s.replace(L, '').replace(R, ''), start, end }
+}
+
+function render({ value, start, end }: TextState): string {
+  return value.slice(0, start) + L + value.slice(start, end) + R + value.slice(end)
+}
+
+function fmt(s: string, action: FormatAction): string {
+  return render(applyFormat(parse(s), action))
+}
+
+const inline = (marker: InlineMarker): FormatAction => ({ kind: 'inline', marker })
+
+describe('inline wrap', () => {
+  it('wraps the selection and keeps the inner text selected', () => {
+    expect(fmt('say ⟦hi⟧ now', inline('**'))).toBe('say **⟦hi⟧** now')
+  })
+
+  it('inserts an empty pair with the cursor between when nothing is selected', () => {
+    expect(fmt('say ⟦⟧now', inline('**'))).toBe('say **⟦⟧**now')
+  })
+
+  it('unwraps when the markers sit just outside the selection', () => {
+    expect(fmt('say **⟦hi⟧** now', inline('**'))).toBe('say ⟦hi⟧ now')
+  })
+
+  it('unwraps when the selection includes the markers', () => {
+    expect(fmt('say ⟦**hi**⟧ now', inline('**'))).toBe('say ⟦hi⟧ now')
+  })
+
+  it('keeps markers outside leading/trailing whitespace in the selection', () => {
+    expect(fmt('a⟦ hi ⟧b', inline('**'))).toBe('a **⟦hi⟧** b')
+  })
+
+  it('italic on a bold selection adds italic rather than stripping bold', () => {
+    expect(fmt('x **⟦hi⟧** y', inline('*'))).toBe('x ***⟦hi⟧*** y')
+  })
+
+  it('removes just bold from bold+italic', () => {
+    expect(fmt('x ***⟦hi⟧*** y', inline('**'))).toBe('x *⟦hi⟧* y')
+  })
+
+  it('removes just italic from bold+italic', () => {
+    expect(fmt('x ***⟦hi⟧*** y', inline('*'))).toBe('x **⟦hi⟧** y')
+  })
+
+  it('strikethrough toggles off without being confused by subscript', () => {
+    expect(fmt('x ~~⟦hi⟧~~ y', inline('~~'))).toBe('x ⟦hi⟧ y')
+    expect(fmt('a ⟦hi⟧ b', inline('~'))).toBe('a ~⟦hi⟧~ b')
+  })
+
+  it('handles inline code and superscript', () => {
+    expect(fmt('run ⟦ls⟧', inline('`'))).toBe('run `⟦ls⟧`')
+    expect(fmt('x⟦2⟧', inline('^'))).toBe('x^⟦2⟧^')
+  })
+
+  it.each(['**', '*', '~~', '~', '`', '^'] as InlineMarker[])('%s: applying twice restores the original', (marker) => {
+    const original = parse('a ⟦b⟧ c')
+    const once = applyFormat(original, inline(marker))
+    expect(once.value).not.toBe(original.value)
+    expect(applyFormat(once, inline(marker))).toEqual(original)
+  })
+})
+
+describe('line prefixes', () => {
+  it('prefixes the current line and moves the cursor with it', () => {
+    expect(fmt('hello⟦⟧', { kind: 'prefix', prefix: 'quote' })).toBe('> hello⟦⟧')
+    expect(fmt('one\ntw⟦⟧o', { kind: 'prefix', prefix: 'quote' })).toBe('one\n> tw⟦⟧o')
+  })
+
+  it('starts a list on a blank line', () => {
+    expect(fmt('⟦⟧', { kind: 'prefix', prefix: 'bullet' })).toBe('- ⟦⟧')
+  })
+
+  it('prefixes every selected line, then toggles them back off', () => {
+    const bullet: FormatAction = { kind: 'prefix', prefix: 'bullet' }
+    expect(fmt('⟦a\nb⟧', bullet)).toBe('⟦- a\n- b⟧')
+    expect(fmt('⟦- a\n- b⟧', bullet)).toBe('⟦a\nb⟧')
+  })
+
+  it('numbers lines sequentially, skipping blank lines, and renumbers existing numbers', () => {
+    const ordered: FormatAction = { kind: 'prefix', prefix: 'ordered' }
+    expect(fmt('⟦a\n\nb⟧', ordered)).toBe('⟦1. a\n\n2. b⟧')
+    expect(fmt('⟦1. a\nb⟧', ordered)).toBe('⟦1. a\n2. b⟧')
+    expect(fmt('⟦1. a\n2. b⟧', ordered)).toBe('⟦a\nb⟧')
+  })
+
+  it('does not include a line the selection only touches at its very start', () => {
+    expect(fmt('a\n⟦b\n⟧c', { kind: 'prefix', prefix: 'bullet' })).toBe('a\n⟦- b⟧\nc')
+  })
+})
+
+describe('headings', () => {
+  it('adds, replaces, and toggles off the heading level', () => {
+    expect(fmt('title⟦⟧', { kind: 'heading', level: 2 })).toBe('## title⟦⟧')
+    expect(fmt('⟦# hi⟧', { kind: 'heading', level: 2 })).toBe('⟦## hi⟧')
+    expect(fmt('⟦## hi⟧', { kind: 'heading', level: 1 })).toBe('⟦# hi⟧')
+    expect(fmt('⟦## hi⟧', { kind: 'heading', level: 2 })).toBe('⟦hi⟧')
+  })
+})
+
+describe('code block', () => {
+  it('inserts an empty fenced block with the cursor on the blank line', () => {
+    expect(fmt('⟦⟧', { kind: 'codeBlock' })).toBe('```\n⟦⟧\n```')
+  })
+
+  it('puts the fences on their own lines when the selection is mid-line', () => {
+    expect(fmt('see ⟦x = 1⟧ here', { kind: 'codeBlock' })).toBe('see \n```\n⟦x = 1⟧\n```\n here')
+  })
+
+  it('does not double the newline when the selection already ends with one', () => {
+    expect(fmt('⟦a\n⟧b', { kind: 'codeBlock' })).toBe('```\n⟦a⟧\n```\nb')
+  })
+})
+
+describe('link', () => {
+  it('wraps the selection and selects the placeholder url', () => {
+    expect(fmt('see ⟦docs⟧', { kind: 'link' })).toBe('see [docs](⟦url⟧)')
+  })
+
+  it('treats a selected url as the target and leaves the cursor in the text brackets', () => {
+    expect(fmt('⟦https://example.com⟧', { kind: 'link' })).toBe('[⟦⟧](https://example.com)')
+  })
+
+  it('inserts a placeholder link with its text selected when nothing is selected', () => {
+    expect(fmt('a ⟦⟧', { kind: 'link' })).toBe('a [⟦link text⟧](url)')
+  })
+})

frontend/src/lib/markdownFormat.ts

@@ -0,0 +1,204 @@
+// #75: pure text transforms behind the composer's formatting toolbar. Each
+// takes the textarea's value plus its selection and returns the same shape,
+// so Composer just applies the result -- keeping this free of React/DOM is
+// what makes the fiddly selection math directly unit-testable.
+export interface TextState {
+  value: string
+  start: number
+  end: number
+}
+
+export type InlineMarker = '**' | '*' | '~~' | '`' | '~' | '^'
+
+export type FormatAction =
+  | { kind: 'inline'; marker: InlineMarker }
+  | { kind: 'prefix'; prefix: 'quote' | 'bullet' | 'ordered' }
+  | { kind: 'heading'; level: 1 | 2 | 3 }
+  | { kind: 'codeBlock' }
+  | { kind: 'link' }
+
+// Markers whose doubled form is a *different* format (`**` bold vs `*`
+// italic, `~~` strikethrough vs `~` subscript), so "is this already
+// wrapped?" has to look at how long the run of marker characters is rather
+// than just whether one is present.
+const DOUBLED_IS_DIFFERENT = new Set(['*', '~'])
+
+// A run of 3 `*` is bold+italic: bold (2) and italic (1) are both "present".
+function hasMarker(marker: string, run: number): boolean {
+  if (marker.length === 2) return run >= 2
+  return DOUBLED_IS_DIFFERENT.has(marker[0]) ? run % 2 === 1 : run >= 1
+}
+
+function applyInline(state: TextState, marker: InlineMarker): TextState {
+  const { value, start, end } = state
+  const ch = marker[0]
+  const m = marker.length
+  const sel = value.slice(start, end)
+
+  // Selection includes the markers themselves (e.g. the user selected the
+  // whole `**word**`) -- unwrap inside the selection.
+  if (sel.length > 0) {
+    let lead = 0
+    while (lead < sel.length && sel[lead] === ch) lead++
+    let trail = 0
+    while (trail < sel.length - lead && sel[sel.length - 1 - trail] === ch) trail++
+    const run = Math.min(lead, trail)
+    if (run > 0 && hasMarker(marker, run) && sel.length > 2 * m) {
+      const inner = sel.slice(m, sel.length - m)
+      return { value: value.slice(0, start) + inner + value.slice(end), start, end: start + inner.length }
+    }
+  }
+
+  // Markers sit just outside the selection. Skipped when the selection has
+  // edge whitespace: markers adjacent to it belong to neighbouring spans
+  // (`*a* and *b*` with " and " selected), not to this selection.
+  const edgeWhitespace = sel.length > 0 && (/^\s/.test(sel) || /\s$/.test(sel))
+  if (!edgeWhitespace) {
+    let before = 0
+    while (start - before - 1 >= 0 && value[start - before - 1] === ch) before++
+    let after = 0
+    while (end + after < value.length && value[end + after] === ch) after++
+    const run = Math.min(before, after)
+    if (run > 0 && hasMarker(marker, run)) {
+      return {
+        value: value.slice(0, start - m) + sel + value.slice(end + m),
+        start: start - m,
+        end: end - m,
+      }
+    }
+  }
+
+  // Nothing selected (or only whitespace): drop in an empty pair, cursor between.
+  if (sel.trim() === '') {
+    return {
+      value: value.slice(0, start) + marker + marker + value.slice(start),
+      start: start + m,
+      end: start + m,
+    }
+  }
+
+  // Markdown doesn't treat `** word**` as bold -- keep the markers hugging
+  // the text, outside any whitespace the selection happens to include.
+  const innerStart = start + (sel.length - sel.trimStart().length)
+  const innerEnd = end - (sel.length - sel.trimEnd().length)
+  return {
+    value:
+      value.slice(0, innerStart) + marker + value.slice(innerStart, innerEnd) + marker + value.slice(innerEnd),
+    start: innerStart + m,
+    end: innerEnd + m,
+  }
+}
+
+// The whole lines a selection touches. A selection that ends right after a
+// newline (i.e. at the very start of the next line) doesn't count that line.
+function lineBounds(value: string, start: number, end: number) {
+  const lineStart = start === 0 ? 0 : value.lastIndexOf('\n', start - 1) + 1
+  const effectiveEnd = end > start && value[end - 1] === '\n' ? end - 1 : end
+  const nextNewline = value.indexOf('\n', effectiveEnd)
+  return { lineStart, lineEnd: nextNewline === -1 ? value.length : nextNewline }
+}
+
+function transformLines(state: TextState, transform: (lines: string[]) => string[]): TextState {
+  const { value, start, end } = state
+  const { lineStart, lineEnd } = lineBounds(value, start, end)
+  const oldBlock = value.slice(lineStart, lineEnd)
+  const newBlock = transform(oldBlock.split('\n')).join('\n')
+  const next = value.slice(0, lineStart) + newBlock + value.slice(lineEnd)
+  if (start === end) {
+    const cursor = Math.max(lineStart, start + (newBlock.length - oldBlock.length))
+    return { value: next, start: cursor, end: cursor }
+  }
+  // Keep the affected lines selected so the same button toggles it back off.
+  return { value: next, start: lineStart, end: lineStart + newBlock.length }
+}
+
+const ORDERED_RE = /^\d+\. /
+
+function applyPrefix(state: TextState, kind: 'quote' | 'bullet' | 'ordered'): TextState {
+  const marker = kind === 'quote' ? '> ' : '- '
+  const has = (line: string) => (kind === 'ordered' ? ORDERED_RE.test(line) : line.startsWith(marker))
+  const strip = (line: string) => (kind === 'ordered' ? line.replace(ORDERED_RE, '') : line.slice(marker.length))
+
+  return transformLines(state, (lines) => {
+    // Blank lines inside a multi-line selection are paragraph breaks, not
+    // list items -- only a lone blank line (cursor on an empty line) gets one.
+    const multi = lines.length > 1
+    const skip = (line: string) => multi && line === ''
+    const targets = lines.filter((line) => !skip(line))
+    if (targets.length > 0 && targets.every(has)) {
+      return lines.map((line) => (has(line) ? strip(line) : line))
+    }
+    let n = 0
+    return lines.map((line) => {
+      if (skip(line)) return line
+      n++
+      if (kind === 'ordered') return `${n}. ${strip(line)}`
+      return has(line) ? line : marker + line
+    })
+  })
+}
+
+const HEADING_RE = /^#{1,6} /
+
+function applyHeading(state: TextState, level: 1 | 2 | 3): TextState {
+  const prefix = '#'.repeat(level) + ' '
+  return transformLines(state, (lines) => {
+    const multi = lines.length > 1
+    const skip = (line: string) => multi && line === ''
+    const targets = lines.filter((line) => !skip(line))
+    if (targets.length > 0 && targets.every((line) => line.startsWith(prefix))) {
+      return lines.map((line) => (line.startsWith(prefix) ? line.slice(prefix.length) : line))
+    }
+    return lines.map((line) => (skip(line) ? line : prefix + line.replace(HEADING_RE, '')))
+  })
+}
+
+// A fence only counts at the start of a line, so mid-line cursors get a
+// newline inserted first.
+function applyCodeBlock(state: TextState): TextState {
+  const { value, start, end } = state
+  const before = value.slice(0, start)
+  const after = value.slice(end)
+  const sel = value.slice(start, end).replace(/\n$/, '')
+  const lead = before.length > 0 && !before.endsWith('\n') ? '\n' : ''
+  const trail = after.length > 0 && !after.startsWith('\n') ? '\n' : ''
+  const next = `${before}${lead}\`\`\`\n${sel}\n\`\`\`${trail}${after}`
+  const innerStart = before.length + lead.length + 4
+  return { value: next, start: innerStart, end: innerStart + sel.length }
+}
+
+function applyLink(state: TextState): TextState {
+  const { value, start, end } = state
+  const sel = value.slice(start, end)
+  let text: string
+  let selStart: number
+  let selEnd: number
+  if (/^https?:\/\/\S+$/.test(sel)) {
+    text = `[](${sel})`
+    selStart = selEnd = start + 1
+  } else if (sel) {
+    text = `[${sel}](url)`
+    selStart = start + sel.length + 3
+    selEnd = selStart + 3
+  } else {
+    text = '[link text](url)'
+    selStart = start + 1
+    selEnd = selStart + 9
+  }
+  return { value: value.slice(0, start) + text + value.slice(end), start: selStart, end: selEnd }
+}
+
+export function applyFormat(state: TextState, action: FormatAction): TextState {
+  switch (action.kind) {
+    case 'inline':
+      return applyInline(state, action.marker)
+    case 'prefix':
+      return applyPrefix(state, action.prefix)
+    case 'heading':
+      return applyHeading(state, action.level)
+    case 'codeBlock':
+      return applyCodeBlock(state)
+    case 'link':
+      return applyLink(state)
+  }
+}

frontend/src/lib/roomIndicators.test.ts

@@ -0,0 +1,56 @@
+import { describe, expect, it } from 'vitest'
+import type { MyRoomItem } from '../types'
+import { clearRoomIndicators } from './roomIndicators'
+
+function makeRoom(overrides: Partial<MyRoomItem> & { id: string }): MyRoomItem {
+  return {
+    name: overrides.id,
+    description: null,
+    is_private: false,
+    is_dm: false,
+    is_archived: false,
+    owner_id: 'owner',
+    created_at: '2026-01-01T00:00:00Z',
+    role: 'member',
+    has_unread: false,
+    has_mention: false,
+    dm_partner: null,
+    email_notifications: false,
+    ...overrides,
+  }
+}
+
+describe('clearRoomIndicators', () => {
+  it('clears has_unread and has_mention on the matching room', () => {
+    const rooms = [makeRoom({ id: 'room-1', has_unread: true, has_mention: true })]
+    const result = clearRoomIndicators(rooms, 'room-1')
+    expect(result[0].has_unread).toBe(false)
+    expect(result[0].has_mention).toBe(false)
+  })
+
+  it('preserves unread state on every other room', () => {
+    const rooms = [
+      makeRoom({ id: 'room-1', has_unread: true, has_mention: true }),
+      makeRoom({ id: 'room-2', has_unread: true, has_mention: false }),
+      makeRoom({ id: 'room-3', has_unread: false, has_mention: false }),
+    ]
+    const result = clearRoomIndicators(rooms, 'room-1')
+    const room2 = result.find((r) => r.id === 'room-2')
+    const room3 = result.find((r) => r.id === 'room-3')
+    expect(room2?.has_unread).toBe(true)
+    expect(room3?.has_unread).toBe(false)
+  })
+
+  it('leaves untouched rooms as the same object reference', () => {
+    const room2 = makeRoom({ id: 'room-2', has_unread: true })
+    const rooms = [makeRoom({ id: 'room-1', has_unread: true }), room2]
+    const result = clearRoomIndicators(rooms, 'room-1')
+    expect(result[1]).toBe(room2)
+  })
+
+  it('is a no-op if the room id is not found', () => {
+    const rooms = [makeRoom({ id: 'room-1', has_unread: true })]
+    const result = clearRoomIndicators(rooms, 'does-not-exist')
+    expect(result[0].has_unread).toBe(true)
+  })
+})

frontend/src/lib/roomIndicators.ts

@@ -0,0 +1,9 @@
+import type { MyRoomItem } from '../types'
+
+// Pulled out of ChatShellPage as a pure function purely so it's directly
+// unit-testable without rendering the whole page -- behavior is unchanged.
+// Only touches the matching room; every other room's object reference (and
+// therefore its unread state) is left untouched.
+export function clearRoomIndicators(rooms: MyRoomItem[], roomId: string): MyRoomItem[] {
+  return rooms.map((r) => (r.id === roomId ? { ...r, has_unread: false, has_mention: false } : r))
+}

frontend/src/pages/ChatShellPage.tsx

@@ -1,4 +1,4 @@
-import { useCallback, useEffect, useState } from 'react'
+import { useCallback, useEffect, useMemo, useState } from 'react'
 import { useNavigate, useParams } from 'react-router-dom'
 import { NetworkError } from '../api/client'
 import { listMyRooms, listRoomMembers } from '../api/rooms'
@@ -12,7 +12,9 @@ import { Sidebar } from '../components/Sidebar'
 import { TopBar } from '../components/TopBar'
 import { useAuth } from '../context/AuthContext'
 import { useChatSocketContext } from '../context/ChatSocketContext'
+import { useDesktopRoomBridge } from '../hooks/useDesktopRoomBridge'
 import { MOBILE_BREAKPOINT, useWindowWidth } from '../hooks/useWindowWidth'
+import { clearRoomIndicators } from '../lib/roomIndicators'
 import type { MyRoomItem, RoomMember } from '../types'
 import './ChatShellPage.css'
 
@@ -60,10 +62,13 @@ export function ChatShellPage() {
 
   const socket = useChatSocketContext()
 
-  const clearRoomIndicators = useCallback((id: string) => {
+  const handleRoomRead = useCallback((id: string) => {
-    setRooms((prev) => prev.map((r) => (r.id === id ? { ...r, has_unread: false, has_mention: false } : r)))
+    setRooms((prev) => clearRoomIndicators(prev, id))
   }, [])
 
+  const unreadRoomCount = useMemo(() => rooms.filter((r) => r.has_unread).length, [rooms])
+  useDesktopRoomBridge(activeRoom?.id, unreadRoomCount)
+
   useEffect(
     () =>
       socket.subscribe((envelope) => {
@@ -134,7 +139,7 @@ export function ChatShellPage() {
               onToggleInfo={() => setInfoOpen((v) => !v)}
               infoOpen={infoOpen}
               socket={socket}
-              onRoomRead={clearRoomIndicators}
+              onRoomRead={handleRoomRead}
             />
           ) : (
             !isMobile && (

frontend/src/pages/HelpPage.tsx

@@ -1,6 +1,6 @@
 import { useEffect, useMemo, useState } from 'react'
 import Markdown from 'markdown-to-jsx'
-import { Link } from 'react-router-dom'
+import { Link, useLocation } from 'react-router-dom'
 import { createMarkdownOptions, preprocessMarkdown } from '../components/MessageContent'
 import { TopBar } from '../components/TopBar'
 import './HelpPage.css'
@@ -20,6 +20,15 @@ export function HelpPage() {
     [content],
   )
 
+  // #75: the composer's "?" links straight to /help#formatting, but the guide
+  // is fetched after the page loads -- the browser's own scroll-to-hash has
+  // already run (and found nothing) by the time the headings exist.
+  const { hash } = useLocation()
+  useEffect(() => {
+    if (!markdownPreview || !hash) return
+    document.getElementById(hash.slice(1))?.scrollIntoView()
+  }, [markdownPreview, hash])
+
   useEffect(() => {
     let cancelled = false
     fetch(GUIDE_URL)

frontend/src/ws/useChatSocket.ts

@@ -10,6 +10,13 @@ interface UseChatSocketOptions {
 const RECONNECT_BASE_DELAY_MS = 1000
 const RECONNECT_MAX_DELAY_MS = 30000
 
+// #76: the backend pings every 30s (WS_PING_INTERVAL_SECONDS in chat.py) --
+// this needs to comfortably tolerate one missed ping plus ordinary network
+// jitter before declaring the connection dead, not fire on the very first
+// late beat.
+const ZOMBIE_TIMEOUT_MS = 65000
+const ZOMBIE_CHECK_INTERVAL_MS = 10000
+
 const desktopMode = isDesktopNotificationsSupported()
 
 // Room join/leave (live message delivery) depends only on visibility --
@@ -51,6 +58,16 @@ export function useChatSocket({ onUnauthenticated }: UseChatSocketOptions) {
   // live WebSocket delivery the user can't actually see will do the job.
   const desiredRoomsRef = useRef(new Set<string>())
   const isVisibleRef = useRef(isVisible())
+  // #76: last time *anything* arrived on the socket (a real message, a
+  // "ping", doesn't matter which) -- the only signal that a connection
+  // sitting at readyState OPEN is actually still alive rather than a
+  // zombie. Without this, a connection that dies without ever sending a
+  // close frame (laptop sleep, a NAT silently dropping an idle mapping)
+  // looks identical to a healthy-but-quiet one: onclose never fires, so the
+  // already-correct reconnect+rejoin logic below never runs, and new
+  // messages just stop arriving until something unrelated (e.g. switching
+  // rooms, which refetches history over plain REST) papers over it.
+  const lastActivityRef = useRef(Date.now())
 
   const sendRoomFrame = useCallback((type: 'join' | 'leave', roomId: string) => {
     const ws = socketRef.current
@@ -99,6 +116,7 @@ export function useChatSocket({ onUnauthenticated }: UseChatSocketOptions) {
         if (hasConnectedBefore) checkForUpdate()
         hasConnectedBefore = true
         reconnectDelay = RECONNECT_BASE_DELAY_MS
+        lastActivityRef.current = Date.now()
         setConnected(true)
         // Re-join whatever rooms were joined before a reconnect -- the
         // server has no memory of a dropped connection's prior state. Only
@@ -122,7 +140,17 @@ export function useChatSocket({ onUnauthenticated }: UseChatSocketOptions) {
 
       ws.onmessage = (event) => {
         if (socketRef.current !== ws) return
-        const envelope = JSON.parse(event.data) as ServerEnvelope
+        lastActivityRef.current = Date.now()
+        const parsed = JSON.parse(event.data)
+        // #76: the server's heartbeat -- purely transport-level, not a
+        // domain event, so it's answered and swallowed right here instead
+        // of being forwarded to subscribers (ServerEnvelope's own type
+        // doesn't include it for exactly that reason).
+        if (parsed.type === 'ping') {
+          ws.send(JSON.stringify({ type: 'pong' }))
+          return
+        }
+        const envelope = parsed as ServerEnvelope
         for (const handler of subscribersRef.current) handler(envelope)
       }
 
@@ -143,10 +171,9 @@ export function useChatSocket({ onUnauthenticated }: UseChatSocketOptions) {
         if (stopped) return
 
         // Unexpected close -- a deploy restarting the app server, a brief
-        // network blip, or (absent any app-level ping/pong) an idle
+        // network blip, or an idle connection getting recycled by a reverse
-        // connection getting recycled by a reverse proxy in front of it.
+        // proxy in front of it. Retry with exponential backoff instead of
-        // Retry with exponential backoff instead of leaving the chat
+        // leaving the chat silently dead until the user manually reloads.
-        // silently dead until the user manually reloads.
         reconnectTimer = setTimeout(connect, reconnectDelay)
         reconnectDelay = Math.min(reconnectDelay * 2, RECONNECT_MAX_DELAY_MS)
       }
@@ -154,9 +181,21 @@ export function useChatSocket({ onUnauthenticated }: UseChatSocketOptions) {
 
     connect()
 
+    // #76: catches the case onclose can't -- a connection that dies without
+    // ever sending a close frame at all (readyState stays OPEN forever) is
+    // otherwise invisible to this hook. Forcing a close here just routes it
+    // through the exact same onclose/reconnect/rejoin path as a normal
+    // disconnect, rather than needing separate recovery logic of its own.
+    const zombieCheckTimer = setInterval(() => {
+      if (Date.now() - lastActivityRef.current > ZOMBIE_TIMEOUT_MS) {
+        socketRef.current?.close()
+      }
+    }, ZOMBIE_CHECK_INTERVAL_MS)
+
     return () => {
       stopped = true
       if (reconnectTimer) clearTimeout(reconnectTimer)
+      clearInterval(zombieCheckTimer)
       socketRef.current?.close()
       socketRef.current = null
     }

frontend/vitest.config.ts

@@ -0,0 +1,13 @@
+import { defineConfig } from 'vitest/config'
+import react from '@vitejs/plugin-react'
+
+// Deliberately separate from vite.config.ts, not an extension of it -- that
+// file's VitePWA plugin does real build-time work (service worker
+// injection, manifest generation) that has nothing to do with running unit
+// tests and would just slow every test run down for no benefit.
+export default defineConfig({
+  plugins: [react()],
+  test: {
+    environment: 'jsdom',
+  },
+})