From 76dfc98a86f4d3eff47e355f17953aad4d7ff013 Mon Sep 17 00:00:00 2001
From: tajniak81 <13187254+tajniak81@users.noreply.github.com>
Date: Sun, 18 Oct 2026 19:33:29 +0200
Subject: [PATCH] Group voice and video calls with MatrixRTC and LiveKit

Every call in the web client now goes through MatrixRTC with a LiveKit
SFU, the model Element Call and Element X use; the legacy 1:1 m.call.*
calls are gone. In a room of two the other person is rung and can answer
or decline; in a bigger room a banner offers to join the call. Calls show
a grid of participant tiles with mute, camera, screen sharing and leave,
and media is end-to-end encrypted in encrypted rooms.

Server:
- MSC4140 delayed events (send/state with a delay, plus the
  delayed_events list/restart/cancel/send API), stored and scheduled, so
  a member whose client drops off is taken out of the call.
- POST /user/{userId}/openid/request_token, which lk-jwt-service uses to
  hand out LiveKit tokens.
- org.matrix.msc4143.rtc_foci in /.well-known/matrix/client, configured
  under client_api.rtc.
- Room presets let members send call membership state.
- Migration 0014 for both SQL dialects.

Deploy: LiveKit and lk-jwt-service in compose (calls.yml) and the helm
chart. Docs: docs/calls.md, configuration and deployment.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 apps/web/README.md                            |  24 +-
 apps/web/cmd/warp-web/main.go                 |   4 +-
 apps/web/internal/host/host.go                |  29 +
 apps/web/internal/host/host_test.go           |  32 +
 apps/web/package.json                         |   1 +
 apps/web/src/components/CallTile.vue          |  58 ++
 apps/web/src/components/CallView.vue          | 286 +++---
 apps/web/src/layouts/ClientShell.vue          |   9 +-
 apps/web/src/matrix/client.ts                 |   3 +
 apps/web/src/matrix/timeline.ts               |  45 +-
 apps/web/src/stores/call.ts                   | 880 ++++++++++++------
 apps/web/src/stores/chat.ts                   |   5 +-
 apps/web/src/views/RoomView.vue               |  42 +-
 apps/web/vite.config.ts                       |   2 +
 deploy/compose/calls.yml                      | 117 +++
 deploy/compose/docker-compose.yml             |   8 +-
 deploy/helm/warp/templates/_helpers.tpl       |  29 +
 deploy/helm/warp/templates/deployment.yaml    |   4 +
 deploy/helm/warp/templates/livekit-jwt.yaml   | 107 +++
 deploy/helm/warp/values.yaml                  |  47 +
 docs/README.md                                |   1 +
 docs/calls.md                                 | 171 ++++
 docs/configuration.md                         |   5 +-
 docs/deployment.md                            |  15 +
 pnpm-lock.yaml                                |  94 ++
 server/internal/clientapi/clientapi.go        |  25 +
 server/internal/clientapi/clientapi_test.go   |  81 +-
 server/internal/clientapi/delayed.go          | 259 ++++++
 server/internal/clientapi/delayed_test.go     | 300 ++++++
 server/internal/clientapi/openid.go           | 106 +++
 server/internal/clientapi/openid_test.go      |  61 ++
 server/internal/clientapi/rooms.go            |  21 +
 server/internal/clientapi/rtc.go              |  51 +
 server/internal/clientapi/voip_test.go        |  24 +
 server/internal/config/config.go              |  48 +
 .../internal/delayedevents/delayedevents.go   | 463 +++++++++
 server/internal/httputil/errors.go            |   5 +
 server/internal/roomserver/create.go          |   8 +
 server/internal/setup/routes.go               |  18 +-
 server/internal/setup/rtc_test.go             |  87 ++
 server/internal/setup/server.go               |  32 +
 server/internal/storage/delayed.go            | 110 +++
 server/internal/storage/delayed_test.go       | 147 +++
 .../migrations/0014_delayed_events_openid.sql |  50 +
 .../migrations/0014_delayed_events_openid.sql |  50 +
 server/internal/storage/sqlstore/delayed.go   | 273 ++++++
 server/internal/storage/sqlstore/sqlstore.go  |  10 +
 server/internal/storage/storage.go            |   8 +
 warp.yaml.example                             |  26 +-
 49 files changed, 3849 insertions(+), 432 deletions(-)
 create mode 100644 apps/web/src/components/CallTile.vue
 create mode 100644 deploy/compose/calls.yml
 create mode 100644 deploy/helm/warp/templates/livekit-jwt.yaml
 create mode 100644 docs/calls.md
 create mode 100644 server/internal/clientapi/delayed.go
 create mode 100644 server/internal/clientapi/delayed_test.go
 create mode 100644 server/internal/clientapi/openid.go
 create mode 100644 server/internal/clientapi/openid_test.go
 create mode 100644 server/internal/clientapi/rtc.go
 create mode 100644 server/internal/delayedevents/delayedevents.go
 create mode 100644 server/internal/setup/rtc_test.go
 create mode 100644 server/internal/storage/delayed.go
 create mode 100644 server/internal/storage/delayed_test.go
 create mode 100644 server/internal/storage/postgres/migrations/0014_delayed_events_openid.sql
 create mode 100644 server/internal/storage/sqlite/migrations/0014_delayed_events_openid.sql
 create mode 100644 server/internal/storage/sqlstore/delayed.go

diff --git a/apps/web/README.md b/apps/web/README.md
index be9e82a..1de27b6 100644
--- a/apps/web/README.md
+++ b/apps/web/README.md
@@ -63,12 +63,24 @@ that one origin.
   them asks you to acknowledge it; a reset since you *verified* them says
   their sessions are no longer trusted, with Verify again or Withdraw
   verification.
-- Voice and video calls in a room with one other person (Matrix 1:1 VoIP,
-  WebRTC between the browsers): ringing, answer with or without video,
-  mute, camera on and off, screen sharing, and a panel that stays up while
-  you move between rooms and expands to fill the window. In an encrypted
-  room the call signalling is encrypted too. Calls outside one network
-  need a TURN server; see `client_api.turn` in the server configuration.
+- Voice and video calls in any room, all through a LiveKit SFU (MatrixRTC,
+  the Element Call model; the old Matrix 1:1 VoIP is not used). Voice and
+  video call buttons in the room header. In a room with one other person
+  the call rings them: an incoming-call card with ring tone, answer, answer
+  without video and decline, and "Calling…" with a ringback tone for the
+  caller until they answer, decline or a minute passes. A call of two shows
+  the other person large and you in the corner; a bigger one is a grid
+  with a tile per person, their camera or screen, and a ring around
+  whoever is speaking. Mute, camera, screen sharing, leave, and a panel
+  that stays up while you move between rooms. A "Join call" banner while
+  one is going on in a room you're not in it. In an encrypted room the media
+  is end-to-end encrypted with per-participant keys. The room list says
+  when a room has a call going on, and the timeline says when one started
+  and ended. It needs `client_api.rtc` on the server and a LiveKit JWT
+  service; see [docs/calls.md](../../docs/calls.md). warp-web proxies
+  `/.well-known/matrix/client` for this, and `-call-origins`
+  (`WARP_WEB_CALL_ORIGINS`) lets the browser reach the JWT service and
+  LiveKit through the Content-Security-Policy.
 - Encryption setup in Settings: cross-signing keys, secret storage and a
   key backup in one step, behind a recovery key shown once. A new session
   verifies itself with the recovery key (or another session) and restores
diff --git a/apps/web/cmd/warp-web/main.go b/apps/web/cmd/warp-web/main.go
index 9e20ff9..e0e56f8 100644
--- a/apps/web/cmd/warp-web/main.go
+++ b/apps/web/cmd/warp-web/main.go
@@ -54,6 +54,8 @@ func run() error {
 		"base URL of the homeserver, proxied for the client (WARP_WEB_HOMESERVER)")
 	public := flag.String("public-homeserver", env("WARP_WEB_PUBLIC_HOMESERVER", ""),
 		"public URL of the homeserver; when set, the browser calls it directly and nothing is proxied (WARP_WEB_PUBLIC_HOMESERVER)")
+	callOrigins := flag.String("call-origins", env("WARP_WEB_CALL_ORIGINS", ""),
+		"space-separated origins of the LiveKit JWT service and SFU the browser may connect to for group calls (WARP_WEB_CALL_ORIGINS)")
 	logFormat := flag.String("log-format", env("WARP_WEB_LOG_FORMAT", "text"), "text or json (WARP_WEB_LOG_FORMAT)")
 	showVersion := flag.Bool("version", false, "print the version and exit")
 	flag.Parse()
@@ -74,7 +76,7 @@ func run() error {
 	}
 	slog.SetDefault(logger)
 
-	opts := host.Options{Logger: logger, Version: version}
+	opts := host.Options{Logger: logger, Version: version, CallOrigins: strings.Fields(*callOrigins)}
 	mode, target := "proxy", *homeserver
 	if *public != "" {
 		u, err := parseURL("public-homeserver", *public)
diff --git a/apps/web/internal/host/host.go b/apps/web/internal/host/host.go
index 82f4faf..ec1aba4 100644
--- a/apps/web/internal/host/host.go
+++ b/apps/web/internal/host/host.go
@@ -41,6 +41,11 @@ type Options struct {
 	Logger *slog.Logger
 	// Transport overrides the proxy's round tripper, for tests.
 	Transport http.RoundTripper
+	// CallOrigins are origins outside the homeserver the browser may
+	// connect to for group calls: the LiveKit JWT service and the LiveKit
+	// SFU's WebSocket, e.g. https://livekit-jwt.example and
+	// wss://livekit.example. They are added to the CSP's connect-src.
+	CallOrigins []string
 }
 
 // proxiedPrefixes are the parts of the homeserver a Matrix client uses: the
@@ -48,6 +53,10 @@ type Options struct {
 // are not reachable through warp-web.
 var proxiedPrefixes = []string{"/_matrix/client/", "/_matrix/media/"}
 
+// wellKnownClientPath is proxied too: it is where the client finds the
+// group call backend (org.matrix.msc4143.rtc_foci).
+const wellKnownClientPath = "/.well-known/matrix/client"
+
 // Config is the body of /config.json, which the client reads on start.
 type Config struct {
 	// HomeserverURL is where the client sends Matrix requests; empty
@@ -78,6 +87,22 @@ func New(opts Options) (http.Handler, error) {
 		cfg.HomeserverURL = strings.TrimRight(u.String(), "/")
 		connect += " " + u.Scheme + "://" + u.Host
 	}
+	for _, raw := range opts.CallOrigins {
+		u, err := url.Parse(strings.TrimRight(raw, "/"))
+		if err != nil || u.Host == "" || u.Path != "" || u.RawQuery != "" ||
+			(u.Scheme != "http" && u.Scheme != "https" && u.Scheme != "ws" && u.Scheme != "wss") {
+			return nil, errors.New("host: a call origin must be an http(s) or ws(s) origin, got " + raw)
+		}
+		connect += " " + u.Scheme + "://" + u.Host
+		// LiveKit falls back from its WebSocket to an HTTP request on
+		// the same host to find out why a connection failed.
+		switch u.Scheme {
+		case "ws":
+			connect += " http://" + u.Host
+		case "wss":
+			connect += " https://" + u.Host
+		}
+	}
 	body, err := json.Marshal(cfg)
 	if err != nil {
 		return nil, err
@@ -167,6 +192,10 @@ func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		_, _ = w.Write([]byte("ok\n"))
 		return
 
+	case p == wellKnownClientPath && h.proxy != nil:
+		h.proxy.ServeHTTP(w, r)
+		return
+
 	case strings.HasPrefix(p, "/_matrix/") || strings.HasPrefix(p, "/_warp/") || strings.HasPrefix(p, "/_synapse/"):
 		// A path that cleans to something else (dot segments, doubled
 		// slashes) is refused rather than normalised: what is allowed
diff --git a/apps/web/internal/host/host_test.go b/apps/web/internal/host/host_test.go
index fad83ab..211764e 100644
--- a/apps/web/internal/host/host_test.go
+++ b/apps/web/internal/host/host_test.go
@@ -304,3 +304,35 @@ func TestNewValidatesHomeserver(t *testing.T) {
 		}
 	}
 }
+
+func TestProxiesWellKnownClient(t *testing.T) {
+	up := newUpstream(t)
+	h := newHandler(t, up, true)
+	rec := do(h, http.MethodGet, "/.well-known/matrix/client", nil)
+	if rec.Code != 200 || len(up.hits) != 1 || up.hits[0].URL.Path != "/.well-known/matrix/client" {
+		t.Fatalf("status %d, hits %d", rec.Code, len(up.hits))
+	}
+	// The server delegation document stays private.
+	if rec := do(h, http.MethodGet, "/.well-known/matrix/server", nil); rec.Code == 200 && len(up.hits) > 1 {
+		t.Errorf("/.well-known/matrix/server was proxied")
+	}
+}
+
+func TestCallOriginsJoinConnectSrc(t *testing.T) {
+	up := newUpstream(t)
+	target, _ := url.Parse(up.srv.URL)
+	h, err := New(Options{Homeserver: target, Client: clientFS,
+		CallOrigins: []string{"https://livekit-jwt.warp.example/", "wss://livekit.warp.example"}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	rec := do(h, http.MethodGet, "/", nil)
+	want := "connect-src 'self' https://livekit-jwt.warp.example wss://livekit.warp.example https://livekit.warp.example;"
+	if csp := rec.Header().Get("Content-Security-Policy"); !strings.Contains(csp, want) {
+		t.Errorf("CSP %q", csp)
+	}
+
+	if _, err := New(Options{Homeserver: target, CallOrigins: []string{"https://x.example/path"}}); err == nil {
+		t.Error("a call origin with a path was accepted")
+	}
+}
diff --git a/apps/web/package.json b/apps/web/package.json
index 7e79c38..94487d9 100644
--- a/apps/web/package.json
+++ b/apps/web/package.json
@@ -13,6 +13,7 @@
   "dependencies": {
     "@warp/ui": "workspace:*",
     "jsqr": "1.4.0",
+    "livekit-client": "2.22.3",
     "matrix-js-sdk": "^44.0.0",
     "pinia": "^3.0.3",
     "qrcode-generator": "1.4.4",
diff --git a/apps/web/src/components/CallTile.vue b/apps/web/src/components/CallTile.vue
new file mode 100644
index 0000000..23b06cf
--- /dev/null
+++ b/apps/web/src/components/CallTile.vue
@@ -0,0 +1,58 @@
+<script setup lang="ts">
+import type { Track } from 'livekit-client'
+import { computed, onBeforeUnmount, ref, watch } from 'vue'
+import { WIcon } from '@warp/ui'
+import MxcAvatar from '@/components/MxcAvatar.vue'
+import type { Tile } from '@/stores/call'
+
+// One person in a group call: their screen or camera, else their avatar,
+// with their name, a muted microphone, and a ring while they speak.
+
+const props = defineProps<{ tile: Tile; compact?: boolean }>()
+
+const videoEl = ref<HTMLVideoElement>()
+const audioEl = ref<HTMLAudioElement>()
+
+const shown = computed(() => props.tile.screen ?? props.tile.camera)
+// Your own camera is mirrored, the way a mirror (and every call app) shows you.
+const mirrored = computed(() => props.tile.local && !props.tile.screen)
+
+function bind(el: HTMLMediaElement | undefined, track: Track | undefined, old: Track | undefined) {
+  if (!el) return
+  if (old && old !== track) old.detach(el)
+  if (track) track.attach(el)
+}
+
+watch([videoEl, shown], ([el, track], [, old]) => bind(el, track, old), { flush: 'post', immediate: true })
+watch([audioEl, () => props.tile.audio], ([el, track], [, old]) => bind(el, track, old), { flush: 'post', immediate: true })
+
+onBeforeUnmount(() => {
+  if (videoEl.value) shown.value?.detach(videoEl.value)
+  if (audioEl.value) props.tile.audio?.detach(audioEl.value)
+})
+</script>
+
+<template>
+  <div
+    :class="[
+      'relative flex min-h-0 items-center justify-center overflow-hidden rounded-md bg-[#1d2126] transition-shadow',
+      tile.speaking ? 'shadow-[0_0_0_3px_#3fb68b]' : '',
+    ]"
+  >
+    <audio v-if="tile.audio" ref="audioEl" autoplay class="hidden" />
+    <video
+      v-show="shown"
+      ref="videoEl"
+      autoplay
+      playsinline
+      muted
+      :class="['h-full w-full', tile.screen ? 'object-contain' : 'object-cover', mirrored && '-scale-x-100']"
+    />
+    <MxcAvatar v-if="!shown" :name="tile.name" :mxc="tile.avatarMxc" :size="compact ? 48 : 88" />
+    <div class="absolute bottom-2 left-2 flex max-w-[calc(100%-1rem)] items-center gap-1 rounded-sm bg-[#000000a6] px-2 py-0.5">
+      <WIcon v-if="tile.micMuted" name="mic-off" :size="14" label="Muted" class="shrink-0 text-[#ff8a80]" />
+      <WIcon v-if="tile.screen" name="screen-share" :size="14" label="Sharing their screen" class="shrink-0" />
+      <span class="caption truncate text-[#eceeee]">{{ tile.local ? `${tile.name} (you)` : tile.name }}</span>
+    </div>
+  </div>
+</template>
diff --git a/apps/web/src/components/CallView.vue b/apps/web/src/components/CallView.vue
index e145282..98c0f06 100644
--- a/apps/web/src/components/CallView.vue
+++ b/apps/web/src/components/CallView.vue
@@ -1,108 +1,74 @@
 <script setup lang="ts">
-import type { CallFeed } from 'matrix-js-sdk/lib/webrtc/callFeed'
-import { computed, onBeforeUnmount, ref, watch, watchEffect } from 'vue'
+import { computed, onBeforeUnmount, ref, watch } from 'vue'
 import { useRouter } from 'vue-router'
-import { WIcon } from '@warp/ui'
+import { WIcon, WSpinner } from '@warp/ui'
 import type { IconName } from '@warp/ui'
+import CallTile from '@/components/CallTile.vue'
 import MxcAvatar from '@/components/MxcAvatar.vue'
 import { formatDuration } from '@/lib/format'
-import { useCall } from '@/stores/call'
+import { useCall, type Tile } from '@/stores/call'
 
-// The call on screen: a ringing card for an incoming call, else a panel in
-// the corner that a video call can expand to fill the window. It sits above
-// every view, so a call goes on while you move between rooms.
+// The call on screen: a ringing card for a call coming in, else the call
+// you're in. A call of two shows the other person large and you in the
+// corner; a bigger one is a grid. The panel shrinks to the corner so the
+// call goes on while you read and write in your rooms, and sits above
+// every view.
 
 const call = useCall()
 const router = useRouter()
-const expanded = ref(false)
-
-function feedVideo(feed: CallFeed | undefined): MediaStream | undefined {
-  if (!feed || feed.isVideoMuted() || !feed.stream.getVideoTracks().length) return undefined
-  return feed.stream
-}
-
-const view = computed(() => {
-  void call.version
-  const c = call.call
-  if (!c) return null
-  const remoteCamera = feedVideo(c.remoteUsermediaFeed)
-  const remoteScreen = c.remoteScreensharingStream
-  const localCamera = feedVideo(c.localUsermediaFeed)
-  const localScreen = c.localScreensharingStream
-  // Their screen beats their camera on the big stage; whatever is left of
-  // theirs or yours goes in the small picture.
-  const main = remoteScreen ?? remoteCamera
-  const pip = remoteScreen && remoteCamera ? remoteCamera : (localScreen ?? localCamera)
-  return {
-    main,
-    pip,
-    pipMirrored: pip !== undefined && pip === localCamera,
-    remoteAudio: c.remoteUsermediaStream,
-    micMuted: c.isMicrophoneMuted(),
-    cameraOn: Boolean(localCamera),
-    sharing: c.isScreensharing(),
-    remoteOnHold: c.isRemoteOnHold(),
-    localOnHold: c.isLocalOnHold(),
-    roomId: c.roomId,
-  }
-})
-
-const stage = computed(() => call.phase !== 'ringing' && Boolean(view.value?.main || view.value?.pip || call.isVideo))
-const canShare = typeof navigator !== 'undefined' && Boolean(navigator.mediaDevices?.getDisplayMedia)
-
-const status = computed(() => {
-  const v = view.value
-  switch (call.phase) {
-    case 'ringing':
-      return call.isVideo ? 'Incoming video call' : 'Incoming voice call'
-    case 'calling':
-      return 'Calling…'
-    case 'connecting':
-      return 'Connecting…'
-    case 'connected':
-      if (v?.localOnHold) return 'You’re on hold'
-      if (v?.remoteOnHold) return 'On hold'
-      return formatDuration(call.length)
-    case 'ended':
-      return call.endReason
-    default:
-      return ''
-  }
-})
-
-// Streams go to the media elements by hand: srcObject is not an attribute.
-const mainEl = ref<HTMLVideoElement>()
-const pipEl = ref<HTMLVideoElement>()
-const audioEl = ref<HTMLAudioElement>()
-
-function bind(el: HTMLMediaElement | undefined, stream: MediaStream | undefined) {
-  if (!el || el.srcObject === (stream ?? null)) return
-  el.srcObject = stream ?? null
-  if (stream) void el.play().catch(() => undefined)
-}
-watchEffect(() => bind(mainEl.value, view.value?.main), { flush: 'post' })
-watchEffect(() => bind(pipEl.value, view.value?.pip), { flush: 'post' })
-watchEffect(() => bind(audioEl.value, view.value?.remoteAudio), { flush: 'post' })
+const expanded = ref(true)
 
 watch(
-  () => call.call,
-  (c) => {
-    if (!c) expanded.value = false
+  () => call.roomId,
+  (rid) => {
+    // Video calls and group calls open full size; a voice call between
+    // two people starts as the panel in the corner.
+    if (rid) expanded.value = call.video || !call.callee
   },
 )
 
-function onKey(e: KeyboardEvent) {
-  if (e.key === 'Escape' && expanded.value) expanded.value = false
-}
-window.addEventListener('keydown', onKey)
-onBeforeUnmount(() => window.removeEventListener('keydown', onKey))
+const remotes = computed(() => call.tiles.filter((t) => !t.local))
+const self = computed(() => call.tiles.find((t) => t.local))
+/** A call of two: the other person on the stage, you in the corner. */
+const pair = computed(() => remotes.value.length === 1)
+/** Ringing them, nobody here yet. */
+const calling = computed(() => call.ringingOut && remotes.value.length === 0)
 
-function openRoom() {
-  const roomId = view.value?.roomId
-  if (!roomId) return
-  expanded.value = false
-  router.push({ name: 'room', params: { roomId } })
-}
+// Whoever shares their screen takes the stage; otherwise the person
+// speaking comes first, so the panel in the corner shows them.
+const ordered = computed(() => {
+  const rank = (t: Tile) => (t.screen ? 0 : t.speaking && !t.local ? 1 : t.local ? 3 : 2)
+  return [...call.tiles].sort((a, b) => rank(a) - rank(b))
+})
+const shown = computed(() => (expanded.value ? ordered.value : ordered.value.slice(0, 1)))
+// The rest still have to be heard while the panel shows only one.
+const hidden = computed(() => (expanded.value ? [] : ordered.value.slice(1).filter((t) => t.audio)))
+
+const columns = computed(() => {
+  const n = shown.value.length
+  if (n <= 1) return 'grid-cols-1'
+  if (n <= 4) return 'grid-cols-1 sm:grid-cols-2'
+  if (n <= 9) return 'grid-cols-2 lg:grid-cols-3'
+  return 'grid-cols-2 md:grid-cols-3 xl:grid-cols-4'
+})
+
+const status = computed(() => {
+  switch (call.phase) {
+    case 'joining':
+      return calling.value ? 'Calling…' : 'Joining…'
+    case 'reconnecting':
+      return 'Reconnecting…'
+    default: {
+      if (calling.value) return 'Calling…'
+      const time = formatDuration(call.length)
+      if (call.callee) return time
+      const n = call.tiles.length
+      return n === 1 ? `Only you so far · ${time}` : `${n} people · ${time}`
+    }
+  }
+})
+
+const canShare = typeof navigator !== 'undefined' && Boolean(navigator.mediaDevices?.getDisplayMedia)
 
 interface Control {
   icon: IconName
@@ -113,23 +79,28 @@ interface Control {
 }
 
 const controls = computed<Control[]>(() => {
-  const v = view.value
-  if (!v) return []
-  if (call.phase === 'ringing') {
-    const list: Control[] = [{ icon: 'phone-off', label: 'Decline', action: call.decline, tone: 'danger' }]
-    if (call.isVideo) list.push({ icon: 'phone', label: 'Answer without video', action: () => call.answer(false) })
-    list.push({ icon: call.isVideo ? 'video' : 'phone', label: 'Answer', action: () => call.answer(), tone: 'accept' })
-    return list
-  }
-  if (call.phase === 'ended') return [{ icon: 'close', label: 'Close', action: call.hangup }]
   const list: Control[] = [
-    { icon: v.micMuted ? 'mic-off' : 'mic', label: v.micMuted ? 'Unmute' : 'Mute', action: call.toggleMic, on: v.micMuted },
-    { icon: v.cameraOn ? 'video' : 'video-off', label: v.cameraOn ? 'Turn camera off' : 'Turn camera on', action: call.toggleCamera, on: !v.cameraOn && call.isVideo },
+    { icon: call.micOn ? 'mic' : 'mic-off', label: call.micOn ? 'Mute' : 'Unmute', action: () => call.toggle('mic'), on: !call.micOn },
+    {
+      icon: call.cameraOn ? 'video' : 'video-off',
+      label: call.cameraOn ? 'Turn camera off' : 'Turn camera on',
+      action: () => call.toggle('camera'),
+      on: !call.cameraOn,
+    },
   ]
   if (canShare && call.phase === 'connected') {
-    list.push({ icon: 'screen-share', label: v.sharing ? 'Stop sharing' : 'Share screen', action: call.toggleScreenShare, on: v.sharing })
+    list.push({ icon: 'screen-share', label: call.sharing ? 'Stop sharing' : 'Share screen', action: () => call.toggle('screen'), on: call.sharing })
   }
-  list.push({ icon: 'phone-off', label: 'Hang up', action: call.hangup, tone: 'danger' })
+  list.push({ icon: 'phone-off', label: calling.value ? 'Cancel call' : 'Leave call', action: () => void call.leave(), tone: 'danger' })
+  return list
+})
+
+const ringControls = computed<Control[]>(() => {
+  const c = call.incoming
+  if (!c) return []
+  const list: Control[] = [{ icon: 'phone-off', label: 'Decline', action: () => void call.decline(), tone: 'danger' }]
+  if (c.video) list.push({ icon: 'phone', label: 'Answer without video', action: () => void call.answer(false) })
+  list.push({ icon: c.video ? 'video' : 'phone', label: 'Answer', action: () => void call.answer(), tone: 'accept' })
   return list
 })
 
@@ -139,37 +110,70 @@ function controlClass(c: Control): string {
   if (c.on) return 'bg-[#eceeee] text-[#111418] hover:bg-[#ffffff]'
   return 'bg-[#ffffff1f] text-[#eceeee] hover:bg-[#ffffff33]'
 }
+
+function openRoom() {
+  const roomId = call.roomId
+  if (!roomId) return
+  expanded.value = false
+  router.push({ name: 'room', params: { roomId } })
+}
+
+function onKey(e: KeyboardEvent) {
+  if (e.key === 'Escape' && expanded.value) expanded.value = false
+}
+window.addEventListener('keydown', onKey)
+onBeforeUnmount(() => window.removeEventListener('keydown', onKey))
 </script>
 
 <template>
   <section
-    v-if="call.call && view"
+    v-if="call.incoming && !call.joined"
+    class="fixed right-4 bottom-4 left-4 z-40 flex flex-col overflow-hidden rounded-lg bg-[#111418] text-[#eceeee] shadow-float sm:left-auto sm:w-[360px]"
+    :aria-label="`Call from ${call.incoming.callerName}`"
+    role="alertdialog"
+  >
+    <div class="flex items-center gap-3 px-4 pt-4">
+      <MxcAvatar :name="call.incoming.callerName" :mxc="call.incoming.callerAvatarMxc" :size="48" />
+      <div class="min-w-0 flex-1">
+        <span class="body-strong block truncate">{{ call.incoming.callerName }}</span>
+        <span class="small block truncate text-[#eceeeeb3]">{{ call.incoming.video ? 'Incoming video call' : 'Incoming voice call' }}</span>
+      </div>
+    </div>
+    <div class="flex items-center justify-center gap-3 px-4 pt-3 pb-4">
+      <button
+        v-for="c in ringControls"
+        :key="c.label"
+        type="button"
+        :class="['flex h-12 w-12 cursor-pointer items-center justify-center rounded-full border-0 transition-colors', controlClass(c)]"
+        :aria-label="c.label"
+        :title="c.label"
+        @click="c.action()"
+      >
+        <WIcon :name="c.icon" :size="22" />
+      </button>
+    </div>
+  </section>
+
+  <section
+    v-if="call.roomId"
     :class="[
       'fixed z-40 flex flex-col overflow-hidden bg-[#111418] text-[#eceeee] shadow-float',
       expanded ? 'inset-0' : 'right-4 bottom-4 left-4 rounded-lg sm:left-auto sm:w-[360px]',
     ]"
-    :aria-label="`Call with ${call.peerName}`"
-    :role="call.phase === 'ringing' ? 'alertdialog' : 'region'"
+    :aria-label="`Call: ${call.title}`"
+    role="region"
   >
-    <audio ref="audioEl" autoplay class="hidden" />
-
-    <div v-if="stage" :class="['relative bg-[#000000]', expanded ? 'min-h-0 flex-1' : 'aspect-video']">
-      <video v-show="view.main" ref="mainEl" autoplay playsinline muted class="h-full w-full object-contain" />
-      <div v-if="!view.main" class="absolute inset-0 flex items-center justify-center">
-        <MxcAvatar :name="call.peerName" :mxc="call.peerAvatarMxc" :size="expanded ? 120 : 72" />
-      </div>
-      <video
-        v-show="view.pip"
-        ref="pipEl"
-        autoplay
-        playsinline
-        muted
-        :class="['absolute right-3 bottom-3 w-1/4 min-w-24 rounded-md bg-[#000000] object-cover shadow-float', view.pipMirrored && '-scale-x-100']"
-      />
+    <div class="flex items-center gap-3 px-4 pt-3">
+      <button type="button" class="min-w-0 flex-1 cursor-pointer border-0 bg-transparent p-0 text-left text-[#eceeee]" @click="openRoom">
+        <span class="body-strong flex items-center gap-2 truncate">
+          {{ call.title }}
+          <WIcon v-if="call.encrypted" name="lock" :size="14" label="End-to-end encrypted" class="shrink-0 text-[#3fb68b]" />
+        </span>
+        <span class="small block truncate text-[#eceeeeb3] tabular-nums" aria-live="polite">{{ status }}</span>
+      </button>
       <button
-        v-if="call.isVideo || view.main"
         type="button"
-        class="absolute top-2 right-2 flex h-9 w-9 cursor-pointer items-center justify-center rounded-full border-0 bg-[#00000080] text-[#eceeee] hover:bg-[#000000b3]"
+        class="flex h-9 w-9 cursor-pointer items-center justify-center rounded-full border-0 bg-[#ffffff1f] text-[#eceeee] hover:bg-[#ffffff33]"
         :aria-label="expanded ? 'Shrink' : 'Expand'"
         :title="expanded ? 'Shrink' : 'Expand'"
         @click="expanded = !expanded"
@@ -178,12 +182,34 @@ function controlClass(c: Control): string {
       </button>
     </div>
 
-    <div class="flex items-center gap-3 px-4 pt-4">
-      <MxcAvatar v-if="!stage" :name="call.peerName" :mxc="call.peerAvatarMxc" :size="48" />
-      <button type="button" class="min-w-0 flex-1 cursor-pointer border-0 bg-transparent p-0 text-left text-[#eceeee]" @click="openRoom">
-        <span class="body-strong block truncate">{{ call.peerName }}</span>
-        <span class="small block truncate text-[#eceeeeb3] tabular-nums" aria-live="polite">{{ status }}</span>
-      </button>
+    <div :class="['relative px-4 pt-3', expanded ? 'min-h-0 flex-1' : '']">
+      <!-- Joining, or ringing someone who hasn't come yet. -->
+      <div
+        v-if="call.phase === 'joining' || calling"
+        :class="['flex flex-col items-center justify-center gap-4', expanded ? 'h-full' : 'aspect-video']"
+      >
+        <MxcAvatar v-if="call.callee" :name="call.callee.name" :mxc="call.callee.avatarMxc" :size="expanded ? 120 : 72" />
+        <WSpinner v-else :size="32" />
+      </div>
+
+      <!-- Two of you: them on the stage, you in the corner. -->
+      <div v-else-if="pair && remotes[0]" :class="['relative', expanded ? 'h-full' : 'aspect-video']">
+        <CallTile :tile="remotes[0]" :compact="!expanded" class="h-full w-full" />
+        <CallTile
+          v-if="self"
+          :tile="self"
+          compact
+          class="absolute right-3 bottom-3 aspect-video w-1/4 min-w-28 shadow-float"
+        />
+      </div>
+
+      <!-- More: a grid, or whoever is speaking when shrunk. -->
+      <template v-else>
+        <div :class="['grid gap-2', expanded ? `h-full auto-rows-fr ${columns}` : 'aspect-video grid-cols-1']">
+          <CallTile v-for="t in shown" :key="t.id" :tile="t" :compact="!expanded" />
+        </div>
+        <CallTile v-for="t in hidden" :key="t.id" :tile="t" class="hidden" />
+      </template>
     </div>
 
     <div class="flex items-center justify-center gap-3 px-4 pt-3 pb-4">
@@ -193,7 +219,7 @@ function controlClass(c: Control): string {
         type="button"
         :class="['flex h-12 w-12 cursor-pointer items-center justify-center rounded-full border-0 transition-colors', controlClass(c)]"
         :aria-label="c.label"
-        :aria-pressed="c.on === undefined || c.tone ? undefined : c.on"
+        :aria-pressed="c.tone ? undefined : c.on"
         :title="c.label"
         @click="c.action()"
       >
diff --git a/apps/web/src/layouts/ClientShell.vue b/apps/web/src/layouts/ClientShell.vue
index dbcb71c..becf360 100644
--- a/apps/web/src/layouts/ClientShell.vue
+++ b/apps/web/src/layouts/ClientShell.vue
@@ -83,6 +83,13 @@ watchEffect(() => {
   document.title = `${n ? `(${n}) ` : ''}${name ? `${name} · ` : ''}Warp`
 })
 
+// A room with a call going on says so in the list, instead of its last message.
+function callPreview(roomId: string): string {
+  if (call.roomId === roomId) return 'You’re in the call'
+  const n = call.inCall(roomId)
+  return n === 1 ? 'Call in progress: 1 person' : `Call in progress: ${n} people`
+}
+
 const ownName = computed(() => profile.displayName || localpart(session.userId))
 </script>
 
@@ -166,7 +173,7 @@ const ownName = computed(() => profile.displayName || localpart(session.userId))
           :key="r.roomId"
           :name="r.name"
           :avatar-mxc="r.avatarMxc"
-          :preview="r.preview"
+          :preview="call.inCall(r.roomId) ? callPreview(r.roomId) : r.preview"
           :time="formatListTime(r.ts)"
           :unread="r.unread"
           :mention="r.highlight > 0"
diff --git a/apps/web/src/matrix/client.ts b/apps/web/src/matrix/client.ts
index 2a6c42e..954114a 100644
--- a/apps/web/src/matrix/client.ts
+++ b/apps/web/src/matrix/client.ts
@@ -68,6 +68,9 @@ export async function startClient(creds: Credentials): Promise<MatrixClient> {
     accessToken: creds.accessToken,
     timelineSupport: true,
     useAuthorizationHeader: true,
+    // Calls are MatrixRTC with LiveKit (stores/call.ts); the SDK's own
+    // 1:1 VoIP, and its polling for TURN servers, stay off.
+    disableVoip: true,
     cryptoCallbacks,
     // Emoji (SAS), and QR codes both ways: shown here, or scanned with
     // the camera.
diff --git a/apps/web/src/matrix/timeline.ts b/apps/web/src/matrix/timeline.ts
index 7defb3f..f5faa79 100644
--- a/apps/web/src/matrix/timeline.ts
+++ b/apps/web/src/matrix/timeline.ts
@@ -114,6 +114,7 @@ function describeCall(ev: MatrixEvent, room: Room): string | null {
     case EventType.CallInvite:
       return `${sender} started a ${isVideoCallInvite(ev) ? 'video' : 'voice'} call`
     case EventType.CallReject:
+    case EventType.RTCDecline:
       return `${sender} declined the call`
     case EventType.CallHangup:
       switch (ev.getContent().reason) {
@@ -131,6 +132,47 @@ function describeCall(ev: MatrixEvent, room: Room): string | null {
   }
 }
 
+/**
+ * Whether a call.member state event (MatrixRTC) says its device is in the
+ * call. Leaving is an empty event; the legacy form lists memberships.
+ */
+export function isActiveCallMember(content: Record<string, unknown>): boolean {
+  if (Object.keys(content).length === 0) return false
+  if (Array.isArray(content.memberships)) return content.memberships.length > 0
+  return true
+}
+
+/**
+ * Follows who is in a room's group call along the timeline, to say when
+ * it started and ended. Each device in the call has a call.member state
+ * event of its own; a member refreshing theirs says nothing.
+ */
+class CallTracker {
+  private readonly inCall = new Set<string>()
+
+  constructor(room: Room) {
+    const start = room.getLiveTimeline().getState(Direction.Backward)
+    for (const ev of start?.getStateEvents(EventType.GroupCallMemberPrefix) ?? []) {
+      if (isActiveCallMember(ev.getContent())) this.inCall.add(ev.getStateKey() ?? '')
+    }
+  }
+
+  describe(ev: MatrixEvent, room: Room): string | null {
+    const key = ev.getStateKey() ?? ''
+    const was = this.inCall.has(key)
+    const now = isActiveCallMember(ev.getContent())
+    if (was === now) return null
+    const sender = nameOf(room, ev.getSender() ?? '')
+    if (now) {
+      const first = this.inCall.size === 0
+      this.inCall.add(key)
+      return first ? `${sender} started a call` : `${sender} joined the call`
+    }
+    this.inCall.delete(key)
+    return this.inCall.size === 0 ? 'The call ended' : `${sender} left the call`
+  }
+}
+
 /** A one-line description of a state change, or null to leave it out. */
 function describeState(ev: MatrixEvent, room: Room): string | null {
   const sender = nameOf(room, ev.getSender() ?? '')
@@ -285,6 +327,7 @@ export function buildTimeline(c: MatrixClient, room: Room): TimelineItem[] {
   const items: TimelineItem[] = []
   let lastTs = 0
   let prev: MessageItem | null = null
+  const calls = new CallTracker(room)
 
   for (const ev of events) {
     const type = ev.getType()
@@ -310,7 +353,7 @@ export function buildTimeline(c: MatrixClient, room: Room): TimelineItem[] {
         }
         continue
       }
-      const text = describeState(ev, room)
+      const text = type === EventType.GroupCallMemberPrefix ? calls.describe(ev, room) : describeState(ev, room)
       if (text) {
         items.push({ kind: 'notice', key, ts, text })
         prev = null
diff --git a/apps/web/src/stores/call.ts b/apps/web/src/stores/call.ts
index bcec574..5d8c463 100644
--- a/apps/web/src/stores/call.ts
+++ b/apps/web/src/stores/call.ts
@@ -1,7 +1,26 @@
-import { CallEvent, CallFeedEvent, createNewMatrixCall, type MatrixCall, type MatrixClient } from 'matrix-js-sdk'
-import { CallDirection, CallErrorCode, CallParty, CallState, CallType, type CallError } from 'matrix-js-sdk/lib/webrtc/call'
-import { CallEventHandlerEvent } from 'matrix-js-sdk/lib/webrtc/callEventHandler'
-import type { CallFeed } from 'matrix-js-sdk/lib/webrtc/callFeed'
+import {
+  ClientEvent,
+  EventType,
+  MatrixEventEvent,
+  RelationType,
+  RoomEvent as MatrixRoomEvent,
+  SyncState,
+  type IRoomTimelineData,
+  type MatrixClient,
+  type MatrixEvent,
+  type Room as MatrixRoom,
+} from 'matrix-js-sdk'
+import { MatrixRTCSessionEvent, MatrixRTCSessionManagerEvents, type MatrixRTCSession } from 'matrix-js-sdk/lib/matrixrtc'
+import {
+  BaseKeyProvider,
+  createKeyMaterialFromBuffer,
+  DisconnectReason,
+  isE2EESupported,
+  Room,
+  RoomEvent,
+  Track,
+  type Participant,
+} from 'livekit-client'
 import { defineStore } from 'pinia'
 import { computed, ref, shallowRef } from 'vue'
 import { errorMessage } from '@/lib/format'
@@ -9,332 +28,665 @@ import { client } from '@/matrix/client'
 import { startTone, stopTone } from '@/matrix/tones'
 import { useToasts } from '@/stores/toasts'
 
-// Voice and video calls between two people: Matrix's 1:1 VoIP (m.call.*
-// events in the room, WebRTC between the browsers), which the SDK runs.
-// In an encrypted room the call events are encrypted like any other; the
-// media itself is always encrypted by WebRTC (DTLS-SRTP).
+// Voice and video calls, all of them: MatrixRTC (MSC4143) with a LiveKit
+// SFU, the way Element Call does them. A call between two people is the
+// same thing as a call between ten, with a ring on top.
 //
-// One call at a time. A call that comes in while one is going is answered
-// "busy", as a phone would.
+// Who is in a room's call is Matrix state (one
+// org.matrix.msc3401.call.member event per device), which the SDK's
+// MatrixRTC session keeps; the media goes through LiveKit, whose token the
+// LiveKit JWT service hands out for an OpenID token from the homeserver.
+// The session also schedules a delayed "left" with the homeserver (MSC4140)
+// and keeps pushing it back, so a member whose browser crashes or loses
+// its connection drops out of the call on its own.
+//
+// Starting a call in a room with one other person rings them: the first
+// member sends an org.matrix.msc4075.rtc.notification, and the other side
+// answers by joining or declines with org.matrix.msc4310.rtc.decline.
+//
+// In an encrypted room the media is end-to-end encrypted too: each member
+// makes its own key, shares it with the others over encrypted to-device
+// messages, and LiveKit encrypts every frame with it (encryptMedia).
+//
+// One call at a time.
 
-export type CallPhase = 'ringing' | 'calling' | 'connecting' | 'connected' | 'ended'
+/** A person (well, a device) in the call. */
+export interface Tile {
+  /** The LiveKit identity: "@user:server:DEVICE". */
+  id: string
+  userId: string
+  name: string
+  avatarMxc?: string
+  local: boolean
+  camera?: Track
+  screen?: Track
+  /** A remote microphone, to play. Your own is never played back. */
+  audio?: Track
+  micMuted: boolean
+  speaking: boolean
+}
 
-/** How long the ended call stays on screen, saying why. */
-const endedLingerMs = 2500
+export type CallPhase = 'joining' | 'connected' | 'reconnecting'
+
+/** A call ringing for you. */
+export interface IncomingCall {
+  roomId: string
+  /** The notification event, which a decline refers to. */
+  eventId: string
+  callerId: string
+  callerName: string
+  callerAvatarMxc?: string
+  roomName: string
+  video: boolean
+  /** When the ring stops on its own (ms since the epoch). */
+  expiresAt: number
+}
+
+/** The MatrixRTC transport this client publishes: LiveKit via the JWT service. */
+interface LivekitTransport {
+  type: 'livekit'
+  livekit_service_url: string
+  livekit_alias: string
+  [key: string]: unknown
+}
+
+/** How long a call rings, unless the notification says less. */
+const ringLifetimeMs = 60_000
+/** The most a received notification may ring for, whatever it says. */
+const maxRingMs = 120_000
+
+/**
+ * Feeds the per-participant keys MatrixRTC hands out to LiveKit's frame
+ * encryption. Each key belongs to one participant and index; there is no
+ * shared key and no ratcheting, the same settings as Element Call, so the
+ * two can be in one call.
+ */
+class MatrixKeyProvider extends BaseKeyProvider {
+  constructor() {
+    super({ ratchetWindowSize: 0, keyringSize: 256 })
+  }
+
+  async setParticipantKey(key: Uint8Array, index: number, identity: string) {
+    const material = await createKeyMaterialFromBuffer(key.buffer.slice(key.byteOffset, key.byteOffset + key.byteLength) as ArrayBuffer)
+    this.onSetEncryptionKey(material, identity, index)
+  }
+}
+
+/** The user of a LiveKit identity lk-jwt-service made: "@alice:example.org:DEVICE". */
+function identityUser(identity: string): string {
+  // The device is after the last colon; a server name may itself have a port.
+  const i = identity.lastIndexOf(':')
+  return i > 0 ? identity.slice(0, i) : identity
+}
+
+/** How many people (not devices) are in a session. */
+function countMembers(session: MatrixRTCSession): number {
+  return new Set(session.memberships.map((m) => m.userId)).size
+}
+
+/** The other person in a room of two, or undefined. */
+function otherOfTwo(room: MatrixRoom, me: string): string | undefined {
+  if (room.getJoinedMemberCount() !== 2) return undefined
+  return room.getJoinedMembers().find((m) => m.userId !== me)?.userId
+}
 
 export const useCall = defineStore('call', () => {
-  const call = shallowRef<MatrixCall | null>(null)
+  /** The room whose call this client is in. */
+  const roomId = ref<string | null>(null)
+  const phase = ref<CallPhase | null>(null)
   /** Bumps on every change the call view shows. */
   const version = ref(0)
-  /** Seconds since the call connected. */
+  /** How many people are in each room's call, for every room with one. */
+  const active = ref<Record<string, number>>({})
+  const lk = shallowRef<Room | null>(null)
+  /** Media is end-to-end encrypted. */
+  const encrypted = ref(false)
+  /** Joined with the camera on. */
+  const video = ref(false)
+  /** Seconds since you joined. */
   const length = ref(0)
-  /** Why the call ended, once it has. */
-  const endReason = ref('')
+  /** We rang someone and they haven't come yet. */
+  const ringingOut = ref(false)
+  /** A call ringing for you. */
+  const incoming = ref<IncomingCall | null>(null)
+
   let attached: MatrixClient | null = null
-  let clearTimer = 0
-  /** The call got as far as connecting media, at some point. */
-  let connected = false
-  /** The feeds whose mute state is listened to. */
-  let feeds: CallFeed[] = []
-
-  const phase = computed<CallPhase | null>(() => {
-    void version.value
-    const c = call.value
-    if (!c) return null
-    switch (c.state) {
-      case CallState.Ringing:
-        return 'ringing'
-      case CallState.Fledgling:
-      case CallState.WaitLocalMedia:
-      case CallState.CreateOffer:
-      case CallState.InviteSent:
-        return c.direction === CallDirection.Inbound ? 'connecting' : 'calling'
-      case CallState.CreateAnswer:
-      case CallState.Connecting:
-        return 'connecting'
-      case CallState.Connected:
-        return 'connected'
-      default:
-        return 'ended'
-    }
-  })
-
-  const isVideo = computed(() => {
-    void version.value
-    return call.value?.type === CallType.Video
-  })
-
-  const peerName = computed(() => {
-    void version.value
-    const c = call.value
-    if (!c) return ''
-    const member = c.getOpponentMember()
-    if (member) return member.name
-    const room = attached?.getRoom(c.roomId)
-    return room?.name ?? c.invitee ?? ''
-  })
-
-  const peerAvatarMxc = computed(() => {
-    void version.value
-    return call.value?.getOpponentMember()?.getMxcAvatarUrl() ?? undefined
-  })
+  let session: MatrixRTCSession | null = null
+  let keyProvider: MatrixKeyProvider | null = null
+  let lengthTimer = 0
+  let ringOutTimer = 0
+  let ringInTimer = 0
+  /** The ring notification we sent, which a decline refers to. */
+  let sentNotification: string | null = null
+  const watched = new Map<string, MatrixRTCSession>()
 
   function bump() {
     version.value++
   }
 
-  // A feed muting its camera or microphone is not a change in the call's
-  // feeds, so each feed is listened to as well.
-  function watchFeeds(c: MatrixCall | null) {
-    for (const f of feeds) {
-      f.off(CallFeedEvent.MuteStateChanged, bump)
-      f.off(CallFeedEvent.NewStream, bump)
-    }
-    feeds = c ? c.getFeeds() : []
-    for (const f of feeds) {
-      f.on(CallFeedEvent.MuteStateChanged, bump)
-      f.on(CallFeedEvent.NewStream, bump)
-    }
+  const joined = computed(() => roomId.value !== null)
+
+  /** Whether this browser can take part in calls at all. */
+  function supported(): boolean {
+    return typeof window !== 'undefined' && 'RTCPeerConnection' in window
   }
 
-  function onFeeds() {
-    watchFeeds(call.value)
-    bump()
-  }
+  // --- Tones --------------------------------------------------------------
 
   function tones() {
-    const p = phase.value
-    if (p === 'ringing') startTone('ring')
-    else if (p === 'calling') startTone('ringback')
+    if (incoming.value && !joined.value) startTone('ring')
+    else if (ringingOut.value) startTone('ringback')
     else stopTone()
   }
 
-  function onState(state: CallState) {
-    if (state === CallState.Connected) connected = true
+  // --- Who is in which room's call ----------------------------------------
+
+  function refresh(rid: string) {
+    const s = watched.get(rid)
+    const n = s ? countMembers(s) : 0
+    const next = { ...active.value }
+    if (n > 0) next[rid] = n
+    else delete next[rid]
+    active.value = next
+    // The caller gave up, or someone else answered for you.
+    if (incoming.value?.roomId === rid && n === 0) clearIncoming()
+    // Someone came: stop ringing them.
+    if (rid === roomId.value && ringingOut.value && n > 1) stopRingingOut()
+  }
+
+  function watchSession(rid: string, s: MatrixRTCSession) {
+    if (watched.get(rid) === s) return
+    watched.get(rid)?.off(MatrixRTCSessionEvent.MembershipsChanged, onMemberships)
+    watched.set(rid, s)
+    s.on(MatrixRTCSessionEvent.MembershipsChanged, onMemberships)
+    refresh(rid)
+    // Memberships are parsed asynchronously: a call already going on when
+    // the room loads only shows up once that is done.
+    void s.initialMembershipCalculated.then(() => {
+      refresh(rid)
+      bump()
+    })
+  }
+
+  /** Follows the call of every room the client knows. */
+  function watchRoom(room: MatrixRoom) {
+    if (!attached) return
+    watchSession(room.roomId, attached.matrixRTC.getRoomSession(room))
+  }
+
+  function watchAllRooms() {
+    for (const r of attached?.getRooms() ?? []) watchRoom(r)
+  }
+
+  function onSync(state: SyncState) {
+    if (state === SyncState.Prepared) watchAllRooms()
+  }
+
+  function onMemberships() {
+    for (const rid of watched.keys()) refresh(rid)
     bump()
-    tones()
   }
 
-  function onLength(seconds: number) {
-    length.value = seconds
+  function onSessionStarted(rid: string, s: MatrixRTCSession) {
+    watchSession(rid, s)
   }
 
-  function onError(err: CallError) {
-    // The hangup that follows says the rest.
-    if (err.code === CallErrorCode.NoUserMedia) {
-      forgetFailedMedia()
-      useToasts().error(isVideo.value ? 'Can’t use your camera or microphone. Check that the browser may use them.' : 'Can’t use your microphone. Check that the browser may use it.')
-    } else {
-      useToasts().error(`Call failed: ${errorMessage(err)}`)
+  function onSessionEnded(rid: string) {
+    refresh(rid)
+  }
+
+  // --- Ringing ------------------------------------------------------------
+
+  /**
+   * A ring notification or a decline arriving live. A ring counts when it
+   * is someone else's, still within its lifetime, mentions you (or the
+   * room), and you aren't in that call already.
+   */
+  function onTimeline(ev: MatrixEvent, room: MatrixRoom | undefined, toStart: boolean | undefined, _removed: boolean, data: IRoomTimelineData) {
+    if (toStart || !data?.liveEvent || !room) return
+    // In an encrypted room this is still ciphertext; onDecrypted has it.
+    if (ev.isEncrypted() && ev.isBeingDecrypted()) return
+    onCallEvent(ev, room)
+  }
+
+  /** An encrypted ring or decline, once it can be read: only recent ones count. */
+  function onDecrypted(ev: MatrixEvent) {
+    if (ev.isDecryptionFailure() || Date.now() - ev.getTs() > maxRingMs) return
+    const room = attached?.getRoom(ev.getRoomId() ?? '')
+    if (room) onCallEvent(ev, room)
+  }
+
+  /** Event IDs already acted on, so a ring isn't taken twice. */
+  const seen = new Set<string>()
+
+  function onCallEvent(ev: MatrixEvent, room: MatrixRoom) {
+    if (!attached) return
+    const type = ev.getType()
+    if (type !== EventType.RTCNotification && type !== EventType.RTCDecline) return
+    const id = ev.getId()
+    if (id) {
+      if (seen.has(id)) return
+      seen.add(id)
     }
-  }
-
-  function onHangup(c: MatrixCall) {
-    if (c !== call.value) return
-    endReason.value = describeHangup(c, connected)
-    bump()
-    stopTone()
-    window.clearTimeout(clearTimer)
-    clearTimer = window.setTimeout(() => {
-      if (call.value === c) release()
-    }, endedLingerMs)
-  }
-
-  function onReplaced(newCall: MatrixCall) {
-    // Both of you called at once: the SDK keeps one of the two calls.
-    show(newCall)
-  }
-
-  function listen(c: MatrixCall, on: boolean) {
-    const m = on ? 'on' : 'off'
-    c[m](CallEvent.State, onState)
-    c[m](CallEvent.FeedsChanged, onFeeds)
-    c[m](CallEvent.LocalHoldUnhold, bump)
-    c[m](CallEvent.RemoteHoldUnhold, bump)
-    c[m](CallEvent.LengthChanged, onLength)
-    c[m](CallEvent.Error, onError)
-    c[m](CallEvent.Hangup, onHangup)
-    c[m](CallEvent.Replaced, onReplaced)
-  }
-
-  function show(c: MatrixCall) {
-    if (call.value) listen(call.value, false)
-    window.clearTimeout(clearTimer)
-    call.value = c
-    connected = false
-    length.value = 0
-    endReason.value = ''
-    listen(c, true)
-    watchFeeds(c)
-    bump()
-    tones()
-  }
-
-  function release() {
-    if (call.value) listen(call.value, false)
-    watchFeeds(null)
-    window.clearTimeout(clearTimer)
-    call.value = null
-    stopTone()
-    bump()
-  }
-
-  function onIncoming(incoming: MatrixCall) {
-    if (call.value && phase.value !== 'ended') {
-      incoming.hangup(CallErrorCode.UserBusy, false)
+    const me = attached.getUserId() ?? ''
+    if (type === EventType.RTCNotification) {
+      if (ev.getSender() === me || roomId.value === room.roomId) return
+      const content = ev.getContent()
+      const mentions = content['m.mentions'] as { user_ids?: string[]; room?: boolean } | undefined
+      if (!mentions?.room && !mentions?.user_ids?.includes(me)) return
+      // A ring for a call of two; in a bigger room the banner says enough.
+      if (content.notification_type !== 'ring' && !otherOfTwo(room, me)) return
+      const sentAt = typeof content.sender_ts === 'number' ? Math.min(content.sender_ts, ev.getTs()) : ev.getTs()
+      const lifetime = Math.min(typeof content.lifetime === 'number' ? content.lifetime : ringLifetimeMs, maxRingMs)
+      const expiresAt = sentAt + lifetime
+      if (expiresAt <= Date.now()) return
+      if (joined.value) return // Busy: you see the banner when you're free.
+      const caller = room.getMember(ev.getSender() ?? '')
+      incoming.value = {
+        roomId: room.roomId,
+        eventId: ev.getId() ?? '',
+        callerId: ev.getSender() ?? '',
+        callerName: caller?.name ?? ev.getSender() ?? '',
+        callerAvatarMxc: caller?.getMxcAvatarUrl() ?? undefined,
+        roomName: room.name,
+        video: content['m.call.intent'] !== 'audio',
+        expiresAt,
+      }
+      window.clearTimeout(ringInTimer)
+      ringInTimer = window.setTimeout(clearIncoming, expiresAt - Date.now())
+      tones()
       return
     }
-    show(incoming)
-    // Hung up (or answered elsewhere) before we did anything.
-    if (incoming.callHasEnded()) onHangup(incoming)
+    if (type === EventType.RTCDecline) {
+      const target = ev.getContent()['m.relates_to']?.event_id
+      if (!target) return
+      // You declined on another of your devices: stop ringing here.
+      if (ev.getSender() === me && incoming.value?.eventId === target) {
+        clearIncoming()
+        return
+      }
+      // The one person you rang said no.
+      if (target === sentNotification && ringingOut.value && room.roomId === roomId.value) {
+        useToasts().info(`${room.getMember(ev.getSender() ?? '')?.name ?? 'They'} declined the call.`)
+        void leave()
+      }
+    }
+  }
+
+  function clearIncoming() {
+    window.clearTimeout(ringInTimer)
+    incoming.value = null
+    tones()
+  }
+
+  function stopRingingOut() {
+    window.clearTimeout(ringOutTimer)
+    ringingOut.value = false
+    tones()
+  }
+
+  function onNotificationSent(sent: { event_id: string; lifetime?: number }) {
+    sentNotification = sent.event_id
+  }
+
+  /** Answers the call ringing for you. */
+  async function answer(withVideo = true) {
+    const call = incoming.value
+    if (!call) return
+    clearIncoming()
+    await join(call.roomId, withVideo && call.video)
+  }
+
+  /** Declines the call ringing for you. The caller stops ringing when it's the two of you. */
+  async function decline() {
+    const call = incoming.value
+    if (!call) return
+    clearIncoming()
+    try {
+      await client().sendEvent(call.roomId, EventType.RTCDecline, {
+        'm.relates_to': { rel_type: RelationType.Reference, event_id: call.eventId },
+      })
+    } catch (e) {
+      console.error('call: decline: ', e)
+    }
   }
 
   /** Starts listening for calls on the running client. */
   function attach() {
     const c = client()
     if (attached === c) return
-    if (attached) attached.off(CallEventHandlerEvent.Incoming, onIncoming)
-    release()
+    if (attached) {
+      attached.matrixRTC.off(MatrixRTCSessionManagerEvents.SessionStarted, onSessionStarted)
+      attached.matrixRTC.off(MatrixRTCSessionManagerEvents.SessionEnded, onSessionEnded)
+      attached.off(ClientEvent.Room, watchRoom)
+      attached.off(ClientEvent.Sync, onSync)
+      attached.off(MatrixRoomEvent.Timeline, onTimeline)
+      attached.off(MatrixEventEvent.Decrypted, onDecrypted)
+    }
+    for (const s of watched.values()) s.off(MatrixRTCSessionEvent.MembershipsChanged, onMemberships)
+    watched.clear()
+    active.value = {}
+    clearIncoming()
+    void leave()
     attached = c
-    c.on(CallEventHandlerEvent.Incoming, onIncoming)
+    c.matrixRTC.on(MatrixRTCSessionManagerEvents.SessionStarted, onSessionStarted)
+    c.matrixRTC.on(MatrixRTCSessionManagerEvents.SessionEnded, onSessionEnded)
+    c.on(ClientEvent.Room, watchRoom)
+    c.on(ClientEvent.Sync, onSync)
+    c.on(MatrixRoomEvent.Timeline, onTimeline)
+    c.on(MatrixEventEvent.Decrypted, onDecrypted)
+    watchAllRooms()
   }
 
-  /** Whether this browser can make calls at all. */
-  function supported(): boolean {
-    return Boolean(attached?.supportsVoip())
-  }
+  // --- Joining ------------------------------------------------------------
 
-  async function place(roomId: string, invitee: string | undefined, video: boolean) {
-    if (call.value && phase.value !== 'ended') {
-      useToasts().error('You’re already in a call.')
-      return
+  /** The LiveKit JWT service to use: the one the call already uses, else this server's. */
+  async function chooseTransport(s: MatrixRTCSession, rid: string): Promise<LivekitTransport> {
+    const oldest = s.memberships[0]
+    const theirs = oldest?.getTransport(oldest)
+    if (theirs && theirs.type === 'livekit' && typeof theirs.livekit_service_url === 'string') {
+      return { type: 'livekit', livekit_service_url: theirs.livekit_service_url, livekit_alias: rid }
     }
-    const c = createNewMatrixCall(client(), roomId, { invitee })
-    if (!c) {
-      useToasts().error('This browser can’t make calls.')
-      return
-    }
-    show(c)
+    const c = client()
+    // The homeserver lists its backends (MSC4143); a server that predates
+    // the endpoint has them in its discovery document instead.
+    let foci: unknown
     try {
-      if (video) await c.placeVideoCall()
-      else await c.placeVoiceCall()
-    } catch (e) {
-      // The SDK has hung up already and said why through CallEvent.Error.
-      console.error('call: ', e)
+      foci = await c._unstable_getRTCTransports()
+    } catch {
+      const res = await fetch(`${c.baseUrl.replace(/\/$/, '')}/.well-known/matrix/client`)
+      if (!res.ok) throw new Error('This server doesn’t offer calls.')
+      const doc = (await res.json()) as Record<string, unknown>
+      foci = doc['org.matrix.msc4143.rtc_foci']
     }
+    const focus = Array.isArray(foci)
+      ? (foci as Record<string, unknown>[]).find((f) => f?.type === 'livekit' && typeof f.livekit_service_url === 'string')
+      : undefined
+    if (!focus) throw new Error('This server doesn’t offer calls.')
+    return { type: 'livekit', livekit_service_url: String(focus.livekit_service_url), livekit_alias: rid }
   }
 
-  /** Answers the ringing call; a video call with the camera off when `video` is false. */
-  async function answer(video = true) {
-    const c = call.value
-    if (!c || phase.value !== 'ringing') return
-    stopTone()
+  /** A LiveKit URL and token, from the JWT service, for an OpenID token. */
+  async function livekitToken(transport: LivekitTransport, rid: string): Promise<{ url: string; jwt: string }> {
+    const c = client()
+    const openid = await c.getOpenIdToken()
+    const res = await fetch(`${transport.livekit_service_url.replace(/\/$/, '')}/sfu/get`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ room: rid, openid_token: openid, device_id: c.getDeviceId() }),
+    })
+    if (!res.ok) throw new Error(`The call service refused to let you in (${res.status}).`)
+    const body = (await res.json()) as { url?: string; jwt?: string }
+    if (!body.url || !body.jwt) throw new Error('The call service gave an unusable answer.')
+    return { url: body.url, jwt: body.jwt }
+  }
+
+  function listen(r: Room) {
+    r.on(RoomEvent.ParticipantConnected, bump)
+      .on(RoomEvent.ParticipantDisconnected, bump)
+      .on(RoomEvent.TrackSubscribed, bump)
+      .on(RoomEvent.TrackUnsubscribed, bump)
+      .on(RoomEvent.TrackMuted, bump)
+      .on(RoomEvent.TrackUnmuted, bump)
+      .on(RoomEvent.LocalTrackPublished, bump)
+      .on(RoomEvent.LocalTrackUnpublished, bump)
+      .on(RoomEvent.ActiveSpeakersChanged, bump)
+      .on(RoomEvent.ParticipantEncryptionStatusChanged, bump)
+      .on(RoomEvent.Reconnecting, () => {
+        phase.value = 'reconnecting'
+      })
+      .on(RoomEvent.Reconnected, () => {
+        phase.value = 'connected'
+      })
+      .on(RoomEvent.Disconnected, (reason?: DisconnectReason) => {
+        if (lk.value !== r) return
+        if (reason !== DisconnectReason.CLIENT_INITIATED) useToasts().error('You were disconnected from the call.')
+        void leave()
+      })
+  }
+
+  function onEncryptionKey(key: Uint8Array, index: number, _membership: unknown, backendIdentity: string) {
+    void keyProvider?.setParticipantKey(key, index, backendIdentity)
+  }
+
+  function onMembershipError(e: unknown) {
+    useToasts().error(`The call stopped working: ${errorMessage(e)}`)
+    void leave()
+  }
+
+  /**
+   * Joins the call in a room, or starts one. Starting a call in a room of
+   * two rings the other person.
+   */
+  async function join(rid: string, withVideo: boolean) {
+    if (roomId.value === rid) return
+    if (roomId.value) await leave()
+    const c = client()
+    const room = c.getRoom(rid)
+    if (!room) return
+    if (incoming.value?.roomId === rid) clearIncoming()
+
+    roomId.value = rid
+    phase.value = 'joining'
+    video.value = withVideo
+    length.value = 0
+    sentNotification = null
+    bump()
+    const s = c.matrixRTC.getRoomSession(room)
+    watchSession(rid, s)
+    session = s
+    const e2ee = room.hasEncryptionStateEvent()
+    encrypted.value = e2ee
+    const me = c.getUserId()!
+    const ringing = countMembers(s) === 0 && otherOfTwo(room, me) !== undefined
     try {
-      await c.answer(true, video && c.type === CallType.Video)
+      if (e2ee && !isE2EESupported()) {
+        throw new Error('This browser can’t encrypt call media, and this room is end-to-end encrypted.')
+      }
+      const transport = await chooseTransport(s, rid)
+      const { url, jwt } = await livekitToken(transport, rid)
+      if (roomId.value !== rid) return
+
+      keyProvider = e2ee ? new MatrixKeyProvider() : null
+      const r = new Room({
+        adaptiveStream: true,
+        dynacast: true,
+        e2ee: keyProvider
+          ? { keyProvider, worker: new Worker(new URL('livekit-client/e2ee-worker', import.meta.url), { type: 'module' }) }
+          : undefined,
+      })
+      lk.value = r
+      listen(r)
+      if (keyProvider) await r.setE2EEEnabled(true)
+
+      // The Matrix side: announce ourselves (and schedule our own delayed
+      // leave), ring the other person if we're the first, and in an
+      // encrypted room start sharing media keys.
+      const deviceId = c.getDeviceId()!
+      s.on(MatrixRTCSessionEvent.EncryptionKeyChanged, onEncryptionKey)
+      s.on(MatrixRTCSessionEvent.MembershipManagerError, onMembershipError)
+      s.on(MatrixRTCSessionEvent.DidSendCallNotification, onNotificationSent)
+      s.join({ userId: me, deviceId, memberId: `${me}:${deviceId}` }, [transport], {
+        manageMediaKeys: e2ee,
+        callIntent: withVideo ? 'video' : 'audio',
+        notificationType: ringing ? 'ring' : countMembers(s) === 0 ? 'notification' : undefined,
+        notificationLifetimeMs: ringLifetimeMs,
+      })
+      if (e2ee) s.reemitEncryptionKeys()
+      if (ringing) {
+        ringingOut.value = true
+        ringOutTimer = window.setTimeout(() => {
+          if (!ringingOut.value || roomId.value !== rid) return
+          useToasts().info('No answer.')
+          void leave()
+        }, ringLifetimeMs)
+        tones()
+      }
+
+      await r.connect(url, jwt)
+      if (roomId.value !== rid) {
+        await r.disconnect()
+        return
+      }
+      phase.value = 'connected'
+      window.clearInterval(lengthTimer)
+      const since = Date.now()
+      lengthTimer = window.setInterval(() => (length.value = Math.floor((Date.now() - since) / 1000)), 1000)
+      bump()
+      try {
+        await r.localParticipant.setMicrophoneEnabled(true)
+      } catch (e) {
+        useToasts().error(`Can’t use your microphone: ${errorMessage(e)}`)
+      }
+      if (withVideo) {
+        try {
+          await r.localParticipant.setCameraEnabled(true)
+        } catch (e) {
+          useToasts().error(`Can’t use your camera: ${errorMessage(e)}`)
+        }
+      }
+      // Browsers only play audio after a gesture; joining was one.
+      await r.startAudio().catch(() => undefined)
+      bump()
     } catch (e) {
       console.error('call: ', e)
+      useToasts().error(errorMessage(e))
+      await leave()
     }
   }
 
-  function decline() {
-    const c = call.value
-    if (!c) return
-    if (phase.value === 'ringing') c.reject()
-    else hangup()
-  }
-
-  function hangup() {
-    const c = call.value
-    if (!c) return
-    if (phase.value === 'ended') release()
-    else c.hangup(CallErrorCode.UserHangup, false)
-  }
-
-  async function toggleMic() {
-    const c = call.value
-    if (!c) return
-    await c.setMicrophoneMuted(!c.isMicrophoneMuted())
+  /** Leaves the call this client is in. */
+  async function leave() {
+    const s = session
+    const r = lk.value
+    session = null
+    lk.value = null
+    keyProvider = null
+    sentNotification = null
+    window.clearInterval(lengthTimer)
+    stopRingingOut()
+    const rid = roomId.value
+    roomId.value = null
+    phase.value = null
     bump()
+    if (s) {
+      s.off(MatrixRTCSessionEvent.EncryptionKeyChanged, onEncryptionKey)
+      s.off(MatrixRTCSessionEvent.MembershipManagerError, onMembershipError)
+      s.off(MatrixRTCSessionEvent.DidSendCallNotification, onNotificationSent)
+    }
+    await Promise.allSettled([r?.disconnect(), s?.leave(5000)])
+    if (rid) refresh(rid)
   }
 
-  async function toggleCamera() {
-    const c = call.value
-    if (!c) return
-    await c.setLocalVideoMuted(!c.isLocalVideoMuted())
-    bump()
-  }
+  // --- What the view shows ------------------------------------------------
 
-  async function toggleScreenShare() {
-    const c = call.value
-    if (!c) return
+  const tiles = computed<Tile[]>(() => {
+    void version.value
+    const r = lk.value
+    const rid = roomId.value
+    if (!r || !rid) return []
+    const room = attached?.getRoom(rid)
+    const speakers = new Set(r.activeSpeakers.map((p) => p.identity))
+    const tile = (p: Participant, local: boolean): Tile => {
+      const userId = identityUser(p.identity)
+      const member = room?.getMember(userId)
+      const cam = p.getTrackPublication(Track.Source.Camera)
+      const screen = p.getTrackPublication(Track.Source.ScreenShare)
+      const mic = p.getTrackPublication(Track.Source.Microphone)
+      return {
+        id: p.identity,
+        userId,
+        name: member?.name ?? userId,
+        avatarMxc: member?.getMxcAvatarUrl() ?? undefined,
+        local,
+        camera: cam?.track && !cam.isMuted ? cam.track : undefined,
+        screen: screen?.track && !screen.isMuted ? screen.track : undefined,
+        audio: !local && mic?.track ? mic.track : undefined,
+        micMuted: !mic || mic.isMuted,
+        speaking: speakers.has(p.identity),
+      }
+    }
+    return [tile(r.localParticipant, true), ...[...r.remoteParticipants.values()].map((p) => tile(p, false))]
+  })
+
+  /** The room's name, or for a call of two, the other person's. */
+  const title = computed(() => {
+    void version.value
+    const rid = roomId.value
+    const room = rid ? attached?.getRoom(rid) : undefined
+    if (!room) return ''
+    const other = otherOfTwo(room, attached?.getUserId() ?? '')
+    return other ? (room.getMember(other)?.name ?? room.name) : room.name
+  })
+
+  /** The person you're calling, for the "ringing" screen of a call of two. */
+  const callee = computed(() => {
+    void version.value
+    const rid = roomId.value
+    const room = rid ? attached?.getRoom(rid) : undefined
+    const other = room ? otherOfTwo(room, attached?.getUserId() ?? '') : undefined
+    const member = other ? room?.getMember(other) : undefined
+    return member ? { name: member.name, avatarMxc: member.getMxcAvatarUrl() ?? undefined } : null
+  })
+
+  const micOn = computed(() => {
+    void version.value
+    return lk.value?.localParticipant.isMicrophoneEnabled ?? false
+  })
+  const cameraOn = computed(() => {
+    void version.value
+    return lk.value?.localParticipant.isCameraEnabled ?? false
+  })
+  const sharing = computed(() => {
+    void version.value
+    return lk.value?.localParticipant.isScreenShareEnabled ?? false
+  })
+
+  async function toggle(what: 'mic' | 'camera' | 'screen') {
+    const p = lk.value?.localParticipant
+    if (!p) return
     try {
-      await c.setScreensharingEnabled(!c.isScreensharing())
+      if (what === 'mic') await p.setMicrophoneEnabled(!p.isMicrophoneEnabled)
+      else if (what === 'camera') await p.setCameraEnabled(!p.isCameraEnabled)
+      else await p.setScreenShareEnabled(!p.isScreenShareEnabled, { audio: true })
     } catch (e) {
-      useToasts().error(`Can’t share your screen: ${errorMessage(e)}`)
+      // Cancelling the browser's screen picker is not an error worth a toast.
+      if (!(e instanceof DOMException && e.name === 'NotAllowedError' && what === 'screen')) {
+        useToasts().error(errorMessage(e))
+      }
     }
     bump()
   }
 
-  function toggleHold() {
-    const c = call.value
-    if (!c) return
-    c.setRemoteOnHold(!c.isRemoteOnHold())
-    bump()
+  /** How many people are in a room's call; 0 when there is none. */
+  function inCall(rid: string): number {
+    return active.value[rid] ?? 0
   }
 
   return {
-    call,
-    version,
-    length,
-    endReason,
+    roomId,
     phase,
-    isVideo,
-    peerName,
-    peerAvatarMxc,
-    attach,
+    version,
+    active,
+    joined,
+    encrypted,
+    video,
+    length,
+    ringingOut,
+    incoming,
+    tiles,
+    title,
+    callee,
+    micOn,
+    cameraOn,
+    sharing,
     supported,
-    place,
+    attach,
+    join,
+    leave,
     answer,
     decline,
-    hangup,
-    toggleMic,
-    toggleCamera,
-    toggleScreenShare,
-    toggleHold,
+    toggle,
+    inCall,
   }
 })
-
-/**
- * The SDK's media handler queues every request for the microphone and
- * camera behind the previous one, and never lets go of a request that
- * failed: once you said no, every later call would fail the same way until
- * the page reloads. Dropping the failed request lets the next call ask again.
- */
-function forgetFailedMedia() {
-  const handler = client().getMediaHandler() as unknown as { getMediaStreamPromise?: Promise<MediaStream> }
-  handler.getMediaStreamPromise = undefined
-}
-
-function describeHangup(c: MatrixCall, connected: boolean): string {
-  switch (c.hangupReason) {
-    case CallErrorCode.UserBusy:
-      return 'Busy'
-    case CallErrorCode.InviteTimeout:
-      return c.direction === CallDirection.Inbound ? 'Missed call' : 'No answer'
-    case CallErrorCode.AnsweredElsewhere:
-      return 'Answered in another session'
-    case CallErrorCode.IceFailed:
-      return 'Couldn’t connect'
-    case CallErrorCode.NoUserMedia:
-      return 'No microphone or camera'
-    case CallErrorCode.Replaced:
-      return 'Call replaced'
-    default:
-      if (!connected) {
-        const outbound = c.direction === CallDirection.Outbound
-        if (c.hangupParty === CallParty.Remote) return outbound ? 'Declined' : 'Missed call'
-        return outbound ? 'Call cancelled' : 'Declined'
-      }
-      return 'Call ended'
-  }
-}
diff --git a/apps/web/src/stores/chat.ts b/apps/web/src/stores/chat.ts
index 650e2f8..a9b835c 100644
--- a/apps/web/src/stores/chat.ts
+++ b/apps/web/src/stores/chat.ts
@@ -60,8 +60,9 @@ export function describeEvent(ev: MatrixEvent, me: string, room: Room, withSende
   // own placeholder text: never show that.
   if (ev.isDecryptionFailure()) return withSender ? `${senderName(ev, me, room)}: Can’t decrypt this message` : 'Can’t decrypt this message'
   if (type === EventType.RoomMessageEncrypted) return 'Encrypted message'
-  if (type === EventType.CallInvite) {
-    const text = isVideoCallInvite(ev) ? 'Video call' : 'Voice call'
+  if (type === EventType.CallInvite || type === EventType.RTCNotification) {
+    const video = type === EventType.CallInvite ? isVideoCallInvite(ev) : ev.getContent()['m.call.intent'] !== 'audio'
+    const text = video ? 'Video call' : 'Voice call'
     return withSender ? `${senderName(ev, me, room)}: ${text}` : text
   }
   if (type !== EventType.RoomMessage && type !== EventType.Sticker) return null
diff --git a/apps/web/src/views/RoomView.vue b/apps/web/src/views/RoomView.vue
index fafd860..8ec017d 100644
--- a/apps/web/src/views/RoomView.vue
+++ b/apps/web/src/views/RoomView.vue
@@ -54,19 +54,25 @@ const canSend = computed(() => {
 
 const infoOpen = ref(false)
 
-// Calls are between two people: offered in a room with just you and one
-// other person in it.
-const callee = computed(() => {
+// Calls, in any room with someone else in it: starting one in a room of
+// two rings the other person. One call at a time, wherever it is.
+const canCall = computed(() => {
   void chat.version
   const r = room.value
-  if (!r || r.getJoinedMemberCount() !== 2) return undefined
-  return r.getJoinedMembers().find((m) => m.userId !== me)?.userId
+  return Boolean(r) && membership.value === KnownMembership.Join && call.supported() && (r?.getJoinedMemberCount() ?? 0) > 1
 })
-const canCall = computed(() => Boolean(callee.value) && call.supported())
-// One call at a time, wherever it is.
-const inCall = computed(() => Boolean(call.call) && call.phase !== 'ended')
-function startCall(video: boolean) {
-  void call.place(props.roomId, callee.value, video)
+const inCall = computed(() => call.joined)
+// A call going on here that you're not in.
+const callHere = computed(() => call.inCall(props.roomId))
+const inThisCall = computed(() => call.roomId === props.roomId)
+const callPeople = computed(() => {
+  void call.version
+  void chat.version
+  const n = callHere.value
+  return n === 1 ? '1 person is' : `${n} people are`
+})
+function joinCall(video: boolean) {
+  void call.join(props.roomId, video)
 }
 
 // Someone in an encrypted room whose identity changed: said before you
@@ -294,13 +300,23 @@ const placeholder = computed(() => `Message ${summary.value?.name ?? 'this room'
         <span v-if="!encrypted" class="caption hidden items-center gap-1 text-ink-muted sm:flex">
           <WIcon name="shield-alert" :size="14" /> Not encrypted
         </span>
-        <template v-if="canCall">
-          <WIconButton icon="phone" label="Voice call" :disabled="inCall" @click="startCall(false)" />
-          <WIconButton icon="video" label="Video call" :disabled="inCall" @click="startCall(true)" />
+        <template v-if="canCall && !callHere">
+          <WIconButton icon="phone" label="Voice call" :disabled="inCall" @click="joinCall(false)" />
+          <WIconButton icon="video" label="Video call" :disabled="inCall" @click="joinCall(true)" />
         </template>
         <WIconButton icon="users" :label="infoOpen ? 'Hide room info' : 'Room info'" :aria-pressed="infoOpen" @click="infoOpen = !infoOpen" />
       </header>
 
+      <div v-if="callHere && canCall && !inThisCall" class="shrink-0 border-b border-line bg-surface px-4 py-2">
+        <WBanner tone="info" icon="video" title="A call is going on in this room">
+          <div class="flex flex-wrap items-center gap-2">
+            <span class="min-w-0 flex-1">{{ callPeople }} in it.</span>
+            <WButton size="sm" :disabled="inCall" @click="joinCall(false)">Join with audio</WButton>
+            <WButton size="sm" variant="primary" :disabled="inCall" @click="joinCall(true)">Join call</WButton>
+          </div>
+        </WBanner>
+      </div>
+
       <RoomTimeline :room="room" :is-direct="summary?.isDirect ?? false" />
 
       <div class="shrink-0 bg-surface-sunken px-4 pt-2 pb-4">
diff --git a/apps/web/vite.config.ts b/apps/web/vite.config.ts
index af84200..4ed93fa 100644
--- a/apps/web/vite.config.ts
+++ b/apps/web/vite.config.ts
@@ -26,6 +26,8 @@ export default defineConfig({
     proxy: {
       '/_matrix/client': { target: homeserver, changeOrigin: true },
       '/_matrix/media': { target: homeserver, changeOrigin: true },
+      // Where the client finds the group call backend (rtc_foci).
+      '/.well-known/matrix/client': { target: homeserver, changeOrigin: true },
     },
   },
 })
diff --git a/deploy/compose/calls.yml b/deploy/compose/calls.yml
new file mode 100644
index 0000000..a5215be
--- /dev/null
+++ b/deploy/compose/calls.yml
@@ -0,0 +1,117 @@
+# Calls for a local Warp: a LiveKit SFU and the LiveKit JWT service
+# (lk-jwt-service), layered over docker-compose.yml.
+#
+#   cd deploy/compose
+#   docker compose -f docker-compose.yml -f calls.yml --profile web up -d --build
+#
+# Then open http://localhost:8080 in a few browsers (or private windows),
+# sign in as different users, and press the voice or video call button in
+# a room: in a room of two it rings the other person.
+#
+# How the pieces find each other:
+#
+#   browser ── /.well-known/matrix/client ──▶ warp     rtc_foci: http://localhost:8070
+#   browser ── openid/request_token ────────▶ warp     an OpenID token
+#   browser ── POST /sfu/get ───────────────▶ jwt      {url, jwt} for the LiveKit room
+#   jwt ───── /_matrix/federation/v1/openid/userinfo ─▶ warp (https://<server_name>:8448)
+#   browser ── ws://localhost:7880 + UDP 7882 ─▶ livekit
+#
+# The JWT service checks a token by asking the user's homeserver over the
+# federation port, with TLS. To make that work with the default server name
+# "localhost", warp gets a federation listener on :8448 with a self-signed
+# certificate, and the JWT service and LiveKit share warp's network
+# namespace, so that "localhost" means warp for all three. This is a local
+# setup: in production, give each its own hostname and real certificates
+# (see docs/calls.md).
+
+services:
+  # Makes the self-signed certificate for warp's federation listener once.
+  calls-cert:
+    image: alpine:3.21
+    restart: "no"
+    entrypoint: ["/bin/sh", "-c"]
+    command:
+      - >-
+        test -f /tls/tls.crt ||
+        (apk add --no-cache openssl >/dev/null &&
+        openssl req -x509 -newkey rsa:2048 -nodes -days 3650
+        -subj "/CN=$${WARP_SERVER_NAME}" -addext "subjectAltName=DNS:$${WARP_SERVER_NAME}"
+        -keyout /tls/tls.key -out /tls/tls.crt &&
+        chmod 644 /tls/tls.key /tls/tls.crt)
+    environment:
+      WARP_SERVER_NAME: ${WARP_SERVER_NAME:-localhost}
+    volumes:
+      - warp-tls:/tls
+
+  warp:
+    depends_on:
+      calls-cert:
+        condition: service_completed_successfully
+    environment:
+      WARP_RTC_LIVEKIT_SERVICE_URL: ${WARP_LIVEKIT_JWT_PUBLIC_URL:-http://localhost:8070}
+      WARP_LISTEN_FEDERATION_ADDRESS: ":8448"
+      WARP_TLS_CERT_FILE: /tls/tls.crt
+      WARP_TLS_KEY_FILE: /tls/tls.key
+    volumes:
+      - warp-tls:/tls:ro
+    # LiveKit and the JWT service live in this container's network
+    # namespace, so their ports are published here.
+    ports:
+      - "8070:8070"       # lk-jwt-service
+      - "7880:7880"       # LiveKit signalling (WebSocket)
+      - "7881:7881"       # LiveKit media over TCP, the fallback
+      - "7882:7882/udp"   # LiveKit media over UDP
+
+  livekit:
+    image: livekit/livekit-server:v1.13.7
+    restart: unless-stopped
+    network_mode: service:warp
+    depends_on:
+      - warp
+    environment:
+      # node_ip is what LiveKit tells browsers to send media to. 127.0.0.1
+      # works for browsers on this machine; set LIVEKIT_NODE_IP to the
+      # machine's LAN address to call from other devices.
+      LIVEKIT_CONFIG: |
+        port: 7880
+        bind_addresses: [""]
+        rtc:
+          tcp_port: 7881
+          udp_port: 7882
+          use_external_ip: false
+          node_ip: ${LIVEKIT_NODE_IP:-127.0.0.1}
+        room:
+          auto_create: false
+        keys:
+          ${LIVEKIT_KEY:-warp}: ${LIVEKIT_SECRET:-warp-local-livekit-secret-change-me-0123456789}
+        logging:
+          level: info
+
+  livekit-jwt:
+    image: ghcr.io/element-hq/lk-jwt-service:0.8.0
+    restart: unless-stopped
+    network_mode: service:warp
+    depends_on:
+      - warp
+      - livekit
+    environment:
+      LIVEKIT_JWT_BIND: ":8070"
+      # The URL handed to browsers, and the one the service creates rooms
+      # through: both reach LiveKit at localhost here.
+      LIVEKIT_URL: ${LIVEKIT_PUBLIC_URL:-ws://localhost:7880}
+      LIVEKIT_KEY: ${LIVEKIT_KEY:-warp}
+      LIVEKIT_SECRET: ${LIVEKIT_SECRET:-warp-local-livekit-secret-change-me-0123456789}
+      # Users of this server may create call rooms on the SFU.
+      LIVEKIT_FULL_ACCESS_HOMESERVERS: ${WARP_SERVER_NAME:-localhost}
+      # warp's federation certificate is self-signed.
+      LIVEKIT_INSECURE_SKIP_VERIFY_TLS: YES_I_KNOW_WHAT_I_AM_DOING
+
+  web:
+    environment:
+      # The browser connects to the JWT service and to LiveKit directly.
+      WARP_WEB_CALL_ORIGINS: >-
+        ${WARP_LIVEKIT_JWT_PUBLIC_URL:-http://localhost:8070}
+        ${LIVEKIT_PUBLIC_URL:-ws://localhost:7880}
+
+volumes:
+  warp-tls:
diff --git a/deploy/compose/docker-compose.yml b/deploy/compose/docker-compose.yml
index 966aebe..0dec621 100644
--- a/deploy/compose/docker-compose.yml
+++ b/deploy/compose/docker-compose.yml
@@ -12,6 +12,12 @@
 # http://localhost:8009; with the web profile, the web client is on
 # http://localhost:8080.
 #
+# For voice and video calls (LiveKit and its JWT service) add calls.yml:
+#
+#   docker compose -f docker-compose.yml -f calls.yml --profile web up -d
+#
+# WARP_PORT moves the homeserver off host port 8008.
+#
 # Create the first administrator once the server is up:
 #
 #   docker compose exec warp warp create-account --username admin --admin
@@ -63,7 +69,7 @@ services:
     volumes:
       - warp-data:/data
     ports:
-      - "8008:8008"
+      - "${WARP_PORT:-8008}:8008"
 
   # The admin panel is optional. Start it with the admin profile:
   #   docker compose --profile admin up -d
diff --git a/deploy/helm/warp/templates/_helpers.tpl b/deploy/helm/warp/templates/_helpers.tpl
index 8be9db1..77b0055 100644
--- a/deploy/helm/warp/templates/_helpers.tpl
+++ b/deploy/helm/warp/templates/_helpers.tpl
@@ -65,3 +65,32 @@ app.kubernetes.io/name: {{ printf "%s-admin" (include "warp.name" .) }}
 app.kubernetes.io/instance: {{ .Release.Name }}
 app.kubernetes.io/component: admin
 {{- end -}}
+
+{{/*
+The LiveKit JWT service for calls, with its own name label like the
+admin panel.
+*/}}
+{{- define "warp.calls.fullname" -}}
+{{- printf "%s-livekit-jwt" (include "warp.fullname" . | trunc 51 | trimSuffix "-") -}}
+{{- end -}}
+
+{{- define "warp.calls.labels" -}}
+helm.sh/chart: {{ printf "%s-%s" .Chart.Name .Chart.Version | replace "+" "_" }}
+{{ include "warp.calls.selectorLabels" . }}
+app.kubernetes.io/managed-by: {{ .Release.Service }}
+{{- end -}}
+
+{{- define "warp.calls.selectorLabels" -}}
+app.kubernetes.io/name: {{ printf "%s-livekit-jwt" (include "warp.name" .) }}
+app.kubernetes.io/instance: {{ .Release.Name }}
+app.kubernetes.io/component: calls
+{{- end -}}
+
+{{/* The JWT service's public URL, advertised to clients: explicit, else its ingress. */}}
+{{- define "warp.calls.serviceURL" -}}
+{{- if .Values.calls.livekitServiceURL -}}
+{{- .Values.calls.livekitServiceURL -}}
+{{- else if and .Values.calls.jwtService.enabled .Values.calls.jwtService.ingress.enabled -}}
+{{- printf "https://%s" .Values.calls.jwtService.ingress.host -}}
+{{- end -}}
+{{- end -}}
diff --git a/deploy/helm/warp/templates/deployment.yaml b/deploy/helm/warp/templates/deployment.yaml
index 2cef553..82b6e75 100644
--- a/deploy/helm/warp/templates/deployment.yaml
+++ b/deploy/helm/warp/templates/deployment.yaml
@@ -97,6 +97,10 @@ spec:
               value: {{ .Values.tracing.sampleRatio | quote }}
             - name: WARP_LOG_FORMAT
               value: json
+            {{- with (include "warp.calls.serviceURL" .) }}
+            - name: WARP_RTC_LIVEKIT_SERVICE_URL
+              value: {{ . | quote }}
+            {{- end }}
             {{- with .Values.extraEnv }}
             {{- toYaml . | nindent 12 }}
             {{- end }}
diff --git a/deploy/helm/warp/templates/livekit-jwt.yaml b/deploy/helm/warp/templates/livekit-jwt.yaml
new file mode 100644
index 0000000..5717e15
--- /dev/null
+++ b/deploy/helm/warp/templates/livekit-jwt.yaml
@@ -0,0 +1,107 @@
+{{- if .Values.calls.jwtService.enabled }}
+{{- $jwt := .Values.calls.jwtService }}
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: {{ include "warp.calls.fullname" . }}
+  labels:
+    {{- include "warp.calls.labels" . | nindent 4 }}
+spec:
+  # The service keeps its state in memory: one replica, unless LIVEKIT_REDIS_URL
+  # is set through extraEnv.
+  replicas: 1
+  selector:
+    matchLabels:
+      {{- include "warp.calls.selectorLabels" . | nindent 6 }}
+  template:
+    metadata:
+      labels:
+        {{- include "warp.calls.selectorLabels" . | nindent 8 }}
+    spec:
+      {{- with .Values.imagePullSecrets }}
+      imagePullSecrets:
+        {{- toYaml . | nindent 8 }}
+      {{- end }}
+      containers:
+        - name: lk-jwt-service
+          image: "{{ $jwt.image.repository }}:{{ $jwt.image.tag }}"
+          imagePullPolicy: {{ $jwt.image.pullPolicy }}
+          ports:
+            - name: http
+              containerPort: 8080
+              protocol: TCP
+          env:
+            - name: LIVEKIT_JWT_BIND
+              value: ":8080"
+            - name: LIVEKIT_URL
+              value: {{ required "calls.jwtService.livekitURL is required" $jwt.livekitURL | quote }}
+            - name: LIVEKIT_KEY
+              valueFrom:
+                secretKeyRef:
+                  name: {{ required "calls.jwtService.existingSecret is required" $jwt.existingSecret }}
+                  key: {{ $jwt.keyKey }}
+            - name: LIVEKIT_SECRET
+              valueFrom:
+                secretKeyRef:
+                  name: {{ $jwt.existingSecret }}
+                  key: {{ $jwt.secretKey }}
+            - name: LIVEKIT_FULL_ACCESS_HOMESERVERS
+              value: {{ $jwt.fullAccessHomeservers | default .Values.serverName | quote }}
+            {{- with $jwt.extraEnv }}
+            {{- toYaml . | nindent 12 }}
+            {{- end }}
+          readinessProbe:
+            httpGet:
+              path: /healthz
+              port: http
+          resources:
+            {{- toYaml $jwt.resources | nindent 12 }}
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: {{ include "warp.calls.fullname" . }}
+  labels:
+    {{- include "warp.calls.labels" . | nindent 4 }}
+spec:
+  type: {{ $jwt.service.type }}
+  ports:
+    - name: http
+      port: {{ $jwt.service.port }}
+      targetPort: http
+      protocol: TCP
+  selector:
+    {{- include "warp.calls.selectorLabels" . | nindent 4 }}
+{{- if $jwt.ingress.enabled }}
+---
+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  name: {{ include "warp.calls.fullname" . }}
+  labels:
+    {{- include "warp.calls.labels" . | nindent 4 }}
+  {{- with $jwt.ingress.annotations }}
+  annotations:
+    {{- toYaml . | nindent 4 }}
+  {{- end }}
+spec:
+  {{- with $jwt.ingress.className }}
+  ingressClassName: {{ . }}
+  {{- end }}
+  {{- with $jwt.ingress.tls }}
+  tls:
+    {{- toYaml . | nindent 4 }}
+  {{- end }}
+  rules:
+    - host: {{ required "calls.jwtService.ingress.host is required" $jwt.ingress.host | quote }}
+      http:
+        paths:
+          - path: /
+            pathType: Prefix
+            backend:
+              service:
+                name: {{ include "warp.calls.fullname" . }}
+                port:
+                  name: http
+{{- end }}
+{{- end }}
diff --git a/deploy/helm/warp/values.yaml b/deploy/helm/warp/values.yaml
index 318f0e0..e4c3c24 100644
--- a/deploy/helm/warp/values.yaml
+++ b/deploy/helm/warp/values.yaml
@@ -190,3 +190,50 @@ admin:
   nodeSelector: {}
   tolerations: []
   affinity: {}
+
+# Calls (MatrixRTC with a LiveKit SFU). Warp only advertises the LiveKit
+# JWT service and answers its OpenID checks; the media goes through LiveKit.
+# See docs/calls.md.
+calls:
+  # The JWT service's public URL, advertised in /.well-known/matrix/client.
+  # Defaults to https://<jwtService.ingress.host> when the chart runs the
+  # service with an ingress; empty and without one, there are no calls.
+  livekitServiceURL: ""
+
+  # lk-jwt-service: hands out LiveKit tokens to users of this server, who
+  # prove who they are with an OpenID token. It checks that token with this
+  # server's federation endpoint at https://<serverName>/.well-known/matrix/server
+  # or <serverName>:8448, so one of the two must reach Warp.
+  jwtService:
+    enabled: false
+    image:
+      repository: ghcr.io/element-hq/lk-jwt-service
+      tag: "0.8.0"
+      pullPolicy: IfNotPresent
+    # The LiveKit SFU's WebSocket URL as browsers reach it, e.g.
+    # wss://livekit.example.org. Run LiveKit itself with its own chart
+    # (https://github.com/livekit/livekit-helm); it needs UDP from clients.
+    livekitURL: wss://livekit.example.org
+    # A secret with the LiveKit API key and secret under these keys.
+    existingSecret: ""
+    keyKey: LIVEKIT_KEY
+    secretKey: LIVEKIT_SECRET
+    # Homeservers whose users may create call rooms on the SFU. Defaults to
+    # serverName.
+    fullAccessHomeservers: ""
+    service:
+      type: ClusterIP
+      port: 8080
+    ingress:
+      enabled: false
+      className: ""
+      annotations: {}
+      host: livekit-jwt.example.org
+      tls: []
+    extraEnv: []
+    resources:
+      requests:
+        cpu: 10m
+        memory: 32Mi
+      limits:
+        memory: 128Mi
diff --git a/docs/README.md b/docs/README.md
index 12b584b..b41f95c 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -13,6 +13,7 @@
 | [federation.md](federation.md) | the Server-Server API: discovery, keys, taking in events, joins across servers, the outbound queue, the switch |
 | [media.md](media.md) | `internal/mediaapi`: uploads, downloads, thumbnails, other servers' media, where the files go |
 | [e2ee.md](e2ee.md) | `internal/keyserver`: device and one-time keys, cross-signing, device list tracking, key backup |
+| [calls.md](calls.md) | voice and video calls with MatrixRTC and LiveKit: ringing, delayed events, OpenID, the JWT service, deploying it |
 | [push.md](push.md) | `internal/pushrules` and `internal/pushserver`: push rules, notification counts, pushers, the push gateway client |
 | [appservices.md](appservices.md) | `internal/appservice`: registration files, namespaces, acting as users, delivering events to bridges |
 | [admin-api.md](admin-api.md) | `/_warp/admin/v1`: the operator API behind the admin panel |
diff --git a/docs/calls.md b/docs/calls.md
new file mode 100644
index 0000000..0b48ec4
--- /dev/null
+++ b/docs/calls.md
@@ -0,0 +1,171 @@
+# Voice and video calls
+
+Every call in Warp's web client, between two people or twenty, is a
+MatrixRTC call (MSC4143) with its media through a LiveKit SFU: the Element
+Call model, which Element X uses too. A call of two is a call with two
+members, plus a ring. The server needs a LiveKit SFU and the LiveKit JWT
+service (`client_api.rtc`); without them there are no calls.
+
+The old Matrix 1:1 VoIP (`m.call.*` events, WebRTC between the two
+browsers) is not used: the web client starts the SDK with `disableVoip`, so
+it neither places nor answers such calls, and shows them only as history in
+the timeline. The server still serves `GET /_matrix/client/v3/voip/turnServer`
+(`client_api.turn`) for other clients that do.
+
+## How a call works
+
+Who is in a room's call is room state: every device in it has an
+`org.matrix.msc3401.call.member` state event (state key
+`_@user:server_DEVICE_m.call`), with the LiveKit service it publishes to.
+The media goes through a LiveKit SFU, which Warp does not run itself.
+
+```
+browser ── GET /.well-known/matrix/client ──────────▶ warp   org.matrix.msc4143.rtc_foci
+        ── GET …/org.matrix.msc4143/rtc/transports ─▶ warp   (the same list, authenticated)
+        ── PUT …/state/org.matrix.msc3401.call.member/<key>
+             ?org.matrix.msc4140.delay=…  (the delayed "left")
+             and then without a delay  (the "joined") ──▶ warp
+        ── POST /user/<me>/openid/request_token ────▶ warp   an OpenID token
+        ── POST <livekit_service_url>/sfu/get ──────▶ lk-jwt-service
+             lk-jwt-service ── GET /_matrix/federation/v1/openid/userinfo ──▶ warp
+        ◀── {url, jwt}
+        ── WebSocket + UDP ─────────────────────────▶ LiveKit
+```
+
+### What the server does
+
+- **Discovery.** With `client_api.rtc.livekit_service_url` set, Warp adds
+  `org.matrix.msc4143.rtc_foci: [{"type": "livekit", "livekit_service_url": …}]`
+  to `/.well-known/matrix/client` and serves the same list at
+  `GET /_matrix/client/unstable/org.matrix.msc4143/rtc/transports`.
+- **Delayed events (MSC4140)**, advertised as `org.matrix.msc4140` in
+  `/versions`. `PUT /rooms/{roomId}/state/{type}/{key}` and
+  `PUT /rooms/{roomId}/send/{type}/{txnId}` take
+  `?org.matrix.msc4140.delay=<ms>`: the event is stored instead of sent,
+  and the answer is `{"delay_id": …}`. Under
+  `/_matrix/client/unstable/org.matrix.msc4140`:
+  - `GET /delayed_events` lists your events as `scheduled` and `finalised`
+    (`?status=` and `?delay_id=` narrow it); `GET /delayed_events/{id}`
+    returns one.
+  - `POST /delayed_events/{id}/{restart|cancel|send}`, or the older
+    `POST /delayed_events/{id}` with `{"action": …}`. These need no access
+    token: the delay ID is the capability.
+
+  A scheduler goroutine sleeps until the next event is due and sends it
+  as the user who scheduled it, through the same pipeline as any event, so
+  power levels and membership still apply; a send that fails is finalised
+  with the error the client would have got. Someone *else* setting the
+  same piece of state cancels a delayed state event, so a stale "left"
+  can't overwrite a newer membership; the owner's own updates don't. Events
+  live in the database (`delayed_events`, migration 14) and survive a
+  restart. Finalised events are kept for a day. `client_api.delayed_events`
+  caps the delay (24h) and how many a user may have (100).
+
+  This is what makes a call robust: a joining member schedules its own
+  empty `call.member` a few seconds out and keeps restarting it while it
+  is in the call. A browser that crashes or loses its network stops
+  restarting it, and Warp removes the member.
+- **OpenID.** `POST /_matrix/client/v3/user/{userId}/openid/request_token`
+  gives a user a one-hour token, which `GET /_matrix/federation/v1/openid/userinfo?access_token=…`
+  turns back into `{"sub": "@user:server"}` for whoever it was handed to.
+  Tokens are stored hashed (`openid_tokens`). The userinfo endpoint is
+  served with federation switched off too: a server that does not
+  federate can still have calls.
+- **Power levels.** New rooms let anyone who may talk join the call:
+  `org.matrix.msc3401.call.member` is at level 0 in the `events` of the
+  default power levels. Rooms created before this keep `state_default`
+  (50) for it, so an ordinary member gets `M_FORBIDDEN` until a moderator
+  sets it to 0.
+
+### Ringing
+
+Starting a call in a room with one other person rings them. The caller's
+MatrixRTC session sends an `org.matrix.msc4075.rtc.notification`
+(`notification_type: "ring"`, a `lifetime` of a minute, `m.call.intent`
+audio or video) when its membership is the first; in a bigger room it
+sends `notification`, which the web client doesn't ring for, since the
+"Join call" banner says enough. The other side shows an incoming-call card
+for a ring that is someone else's, mentions them or the room, and is
+within its lifetime, until they answer (join the call), decline (an
+`org.matrix.msc4310.rtc.decline` referencing the notification, which also
+stops the ring on their other devices), the caller leaves, or it expires.
+The caller hears a ringback until someone joins, and gives up on a decline
+or after the minute. In an encrypted room both events are encrypted like
+any other.
+
+The SDK's own validator for received notifications expects MSC4354 sticky
+events and `m.rtc.slot` state, which Warp doesn't serve yet, so the web
+client applies the receiving rules itself.
+
+### What the web client does
+
+`src/stores/call.ts` uses the SDK's MatrixRTC session
+(`client.matrixRTC.getRoomSession(room)`), publishing the transport
+`{type: "livekit", livekit_service_url, livekit_alias: <room ID>}` (the one
+the call already uses, else this server's), gets a LiveKit token from
+`/sfu/get`, and connects with `livekit-client`. In an encrypted room it
+joins with `manageMediaKeys`: each member makes its own media key and
+sends it to the others over encrypted to-device messages, and a
+`BaseKeyProvider` hands each key to LiveKit's frame encryption for that
+participant (`@user:server:DEVICE`). The settings (no shared key, no
+ratcheting) match Element Call's, so the two can share a call.
+
+### Running it
+
+Locally, [`deploy/compose/calls.yml`](../deploy/compose/calls.yml) adds
+LiveKit and lk-jwt-service to the Compose setup:
+
+```sh
+cd deploy/compose
+WARP_REGISTRATION_ENABLED=true docker compose -f docker-compose.yml -f calls.yml --profile web up -d --build
+```
+
+Then sign in as different users at <http://localhost:8080>,
+<http://127.0.0.1:8080> and <http://[::1]:8080> (different origins keep
+separate sessions in one browser). A voice or video call in a room of two
+rings the other person; in a room of three or more the others see a "Join
+call" banner. `WARP_PORT` and `WARP_WEB_PORT` move the homeserver and web client
+off 8008 and 8080 (then set `WARP_PUBLIC_BASEURL` to match).
+
+The JWT service checks an OpenID token by asking the user's homeserver
+over its federation port with TLS. For the server name `localhost` that
+means `https://localhost:8448`, so the file gives Warp a federation
+listener with a self-signed certificate (`LIVEKIT_INSECURE_SKIP_VERIFY_TLS`
+accepts it) and runs LiveKit and the JWT service in Warp's network
+namespace, where `localhost` is Warp. One consequence: when the `warp`
+container is recreated on its own, the other two lose their network. Run
+`up` for the whole file, not for one service, or recreate them with
+`docker compose -f docker-compose.yml -f calls.yml up -d --force-recreate livekit livekit-jwt`.
+LiveKit advertises `127.0.0.1` for media; set `LIVEKIT_NODE_IP` to the
+machine's LAN address to call from other devices.
+
+In production, give each piece its own hostname and a real certificate:
+
+- **LiveKit**, reachable by browsers on TCP 7880 behind TLS (`wss://`),
+  and UDP (7882, or a port range) and TCP 7881 for media. See LiveKit's
+  own deployment guide or its Helm chart.
+- **lk-jwt-service** behind TLS, with `LIVEKIT_URL` (the `wss://` URL),
+  `LIVEKIT_KEY` / `LIVEKIT_SECRET` (LiveKit's API key) and
+  `LIVEKIT_FULL_ACCESS_HOMESERVERS` (your server name). The Helm chart
+  runs it with `calls.jwtService.enabled`.
+- **Warp** with `client_api.rtc.livekit_service_url` set to the JWT
+  service's URL. The JWT service must reach
+  `https://<server_name>/.well-known/matrix/server` (a delegation to the
+  host that serves Warp) or `<server_name>:8448`. Note that Warp serves
+  `/.well-known/matrix/server` only with federation on; with it off,
+  serve the delegation file from the server name's web server, as you
+  would for `/.well-known/matrix/client`.
+- **warp-web**: `WARP_WEB_CALL_ORIGINS="https://livekit-jwt.example.org wss://livekit.example.org"`
+  lets the browser reach both through its Content-Security-Policy.
+
+### Known gaps
+
+- Calls only use the legacy `org.matrix.msc3401.call.member` state events,
+  not the sticky `m.rtc.member` events of newer MatrixRTC drafts.
+- `org.matrix.msc4140.parent_delay_id` (chained delayed events) is
+  refused, and a delayed send's transaction ID is not deduplicated.
+- No ring for calls in rooms of more than two (only the banner), no
+  MSC4354 sticky events, and no MSC4195 homeserver-side LiveKit token
+  endpoint (`rtc/livekit/get_token`).
+- Calls from clients that only do legacy 1:1 VoIP (`m.call.*`) don't ring
+  in the web client.
diff --git a/docs/configuration.md b/docs/configuration.md
index 79d5734..fc5760f 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -62,10 +62,13 @@ List-valued variables are comma-separated. A single `-` clears a list:
 | `client_api.rate_limit.join.burst` / `.interval` | — | `10` / `1s` | The two join endpoints. |
 | `client_api.rate_limit.sync.burst` / `.interval` | — | `100` / `20ms` | `/sync` and the writes behind it: typing, receipts, to-device, presence. |
 | `client_api.rate_limit.media.burst` / `.interval` | — | `100` / `20ms` | Media downloads and thumbnails: a client opening a room asks for every avatar at once. Uploads are in the default bucket. |
-| `client_api.turn.uris` | `WARP_TURN_URIS` | `[]` | `turn:`, `turns:` and `stun:` URIs for calls. Empty = no relay; `/voip/turnServer` answers `{}`. |
+| `client_api.turn.uris` | `WARP_TURN_URIS` | `[]` | `turn:`, `turns:` and `stun:` URIs for other clients' legacy 1:1 VoIP calls (the web client calls through LiveKit and doesn't use them). Empty = no relay; `/voip/turnServer` answers `{}`. |
 | `client_api.turn.shared_secret` | `WARP_TURN_SHARED_SECRET` | — | coturn's `static-auth-secret`: each user gets expiring TURN REST API credentials. |
 | `client_api.turn.user_lifetime` | `WARP_TURN_USER_LIFETIME` | `1h` | How long shared-secret credentials last. |
 | `client_api.turn.username` / `.password` | `WARP_TURN_USERNAME` / `WARP_TURN_PASSWORD` | — | Static credentials, used only without a shared secret. |
+| `client_api.rtc.livekit_service_url` | `WARP_RTC_LIVEKIT_SERVICE_URL` | — | Base URL of the LiveKit JWT service (lk-jwt-service) for calls, advertised in `/.well-known/matrix/client` as `org.matrix.msc4143.rtc_foci`. Empty = no calls. See [calls.md](calls.md). |
+| `client_api.delayed_events.max_delay` | `WARP_DELAYED_EVENTS_MAX_DELAY` | `24h` | Longest delay a client may give a delayed event (MSC4140). `0` turns delayed events off and stops advertising `org.matrix.msc4140`; calls then can't remove a member whose client vanished. |
+| `client_api.delayed_events.max_per_user` | `WARP_DELAYED_EVENTS_MAX_PER_USER` | `100` | How many delayed events one user may have scheduled at once. |
 | `sync.presence` | `WARP_SYNC_PRESENCE` | `false` | Off by default; see below. |
 | `sync.typing_timeout` | `WARP_SYNC_TYPING_TIMEOUT` | `30s` | How long a typing notification lasts, and the cap on what a client may ask for. |
 | `sync.long_poll_timeout` | `WARP_SYNC_LONG_POLL_TIMEOUT` | `30s` | The cap on a `/sync` `?timeout=`. |
diff --git a/docs/deployment.md b/docs/deployment.md
index e439a89..26a75ab 100644
--- a/docs/deployment.md
+++ b/docs/deployment.md
@@ -135,6 +135,21 @@ already public behind its own proxy, set `WARP_WEB_PUBLIC_HOMESERVER` to
 its URL instead: the browser then calls it directly and warp-web serves
 only the client. See [apps/web](../apps/web/README.md).
 
+## Calls
+
+Calls need a LiveKit SFU and the LiveKit JWT service next to Warp.
+For a local try, `deploy/compose/calls.yml` adds both:
+
+```sh
+cd deploy/compose
+WARP_REGISTRATION_ENABLED=true docker compose -f docker-compose.yml -f calls.yml --profile web up -d --build
+```
+
+The Helm chart can run the JWT service (`calls.jwtService.enabled`) and
+sets `client_api.rtc.livekit_service_url` from it; LiveKit itself runs
+from its own chart. See [calls.md](calls.md) for how the pieces find each
+other and what production needs.
+
 ## Reverse proxy
 
 Behind a proxy that terminates TLS:
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 8311747..b734d32 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -71,6 +71,9 @@ importers:
       jsqr:
         specifier: 1.4.0
         version: 1.4.0
+      livekit-client:
+        specifier: 2.22.3
+        version: 2.22.3(@types/dom-mediacapture-record@1.0.22)
       matrix-js-sdk:
         specifier: ^44.0.0
         version: 44.0.0
@@ -131,6 +134,9 @@ packages:
     resolution: {integrity: sha512-Vj1jF3cPfxg7OAfoI7QnVKLoILlm2JF9pnVHrX8qx7AHMiYWT+NDAA7jChlNgRS4WTLc/fD1lXLmPixluj+3Gg==}
     engines: {node: '>=6.9.0'}
 
+  '@bufbuild/protobuf@1.10.1':
+    resolution: {integrity: sha512-wJ8ReQbHxsAfXhrf9ixl0aYbZorRuOWpBNzm8pL8ftmSxQx/wnJD5Eg861NwJU/czy2VXFIebCeZnZrI9rktIQ==}
+
   '@esbuild/aix-ppc64@0.28.2':
     resolution: {integrity: sha512-XExcO+dvLKvVtNTibSTBej1NCAbaGhWn9Ww1ZPx80qsahhPFe/8jgWP0IchNe0F3HwkU7n8ejhH8bjonqht8mQ==}
     engines: {node: '>=18'}
@@ -303,6 +309,12 @@ packages:
   '@jridgewell/trace-mapping@0.3.31':
     resolution: {integrity: sha512-zzNR+SdQSDJzc8joaeP8QQoCQr8NuYx2dIIytl1QeBEZHJ9uW6hebsrYgbz8hJwUQao3TWCMtmfV8Nu1twOLAw==}
 
+  '@livekit/mutex@1.1.1':
+    resolution: {integrity: sha512-EsshAucklmpuUAfkABPxJNhzj9v2sG7JuzFDL4ML1oJQSV14sqrpTYnsaOudMAw9yOaW53NU3QQTlUQoRs4czw==}
+
+  '@livekit/protocol@1.50.4':
+    resolution: {integrity: sha512-L1uggNQAqyY21smQY8AllyOYbcv9Me9TaxwuLytL1R8ck9nbYPmQLNwEDi3pOFGAMa5F8I2nUi2Jc59W5awxlA==}
+
   '@matrix-org/matrix-sdk-crypto-wasm@18.9.0':
     resolution: {integrity: sha512-NtLzNDTEfNASBjNCTGZHuk7N0jrQhS6Zx2CM857rCHZYYh/rpbKGQNrJ7azktm4S1P5Jy3WU3nwJTGohGw26qQ==}
     engines: {node: '>= 18'}
@@ -531,6 +543,9 @@ packages:
     peerDependencies:
       vite: ^5.2.0 || ^6 || ^7 || ^8
 
+  '@types/dom-mediacapture-record@1.0.22':
+    resolution: {integrity: sha512-mUMZLK3NvwRLcAAT9qmcK+9p7tpU2FHdDsntR3YI4+GY88XrgG4XiE7u1Q2LAN2/FZOz/tdMDC3GQCR4T8nFuw==}
+
   '@types/estree@1.0.9':
     resolution: {integrity: sha512-GhdPgy1el4/ImP05X05Uw4cw2/M93BCUmnEvWZNStlCzEKME4Fkk+YpoA5OiHNQmoS7Cafb8Xa3Pya8m1Qrzeg==}
 
@@ -676,6 +691,9 @@ packages:
     resolution: {integrity: sha512-AC/7JofJvZGrrneWNaEnJeOLUx+JlGt7tNa0wZiRPT4MY1wmfKjt2+6O2p2uz2+skll8OZZmJMNqeke7kKbNgQ==}
     hasBin: true
 
+  jose@6.2.12:
+    resolution: {integrity: sha512-9NiFmJEex0sy2Dk58j2UGBSHgUs2ypF9eZSu4L6vjOX3Dp96Sw1F3uL+H+D1sx02jZZdzUT0HgvCy59CuvXcWw==}
+
   jsqr@1.4.0:
     resolution: {integrity: sha512-dxLob7q65Xg2DvstYkRpkYtmKm2sPJ9oFhrhmudT1dZvNFFTlroai3AWSpLey/w5vMcLBXRgOJsbXpdN9HzU/A==}
 
@@ -749,10 +767,19 @@ packages:
     resolution: {integrity: sha512-NXYBzinNrblfraPGyrbPoD19C1h9lfI/1mzgWYvXUTe414Gz/X1FD2XBZSZM7rRTrMA8JL3OtAaGifrIKhQ5yQ==}
     engines: {node: '>= 12.0.0'}
 
+  livekit-client@2.22.3:
+    resolution: {integrity: sha512-jw9zBKXY5Gtr5MZ7vEON3QhMNccuDvYHck1PFSyG1aaateQPqgKZFBMgZkFZaXHIf9RV4MDW5xpTK2b/+qbwOg==}
+    peerDependencies:
+      '@types/dom-mediacapture-record': ^1
+
   loglevel@1.9.2:
     resolution: {integrity: sha512-HgMmCqIJSAKqo68l0rS2AanEWfkxaZ5wNiEFb5ggm08lDs9Xl2KxBlX3PTcaD2chBM1gXAYf491/M2Rv8Jwayg==}
     engines: {node: '>= 0.6.0'}
 
+  machina@7.0.1:
+    resolution: {integrity: sha512-0Xkgs8NeBvO2hW6bjJT8ewLWrMfh1haMPstaghpASWjXkLjRhtDiaJG1Kb7mslaOHxZYxpH7PIjpmirRVYbMMA==}
+    engines: {node: '>=22.22'}
+
   magic-string@0.30.21:
     resolution: {integrity: sha512-vd2F4YUyEXKGcLHoq+TEyCjxueSeHnFxyyjNp80yg0XV4vUhnDer/lvvlqM/arB5bXQN5K2/3oinyCRyx8T2CQ==}
 
@@ -818,10 +845,20 @@ packages:
     engines: {node: '>=18.0.0', npm: '>=8.0.0'}
     hasBin: true
 
+  rxjs@7.8.2:
+    resolution: {integrity: sha512-dhKf903U/PQZY6boNNtAGdWbG85WAbjT/1xYoZIC7FAY0yWapOBQVsVrDl58W86//e1VpMNBtRV4MaXfdMySFA==}
+
+  sdp-transform@2.15.0:
+    resolution: {integrity: sha512-KrOH82c/W+GYQ0LHqtr3caRpM3ITglq3ljGUIb8LTki7ByacJZ9z+piSGiwZDsRyhQbYBOBJgr2k6X4BZXi3Kw==}
+    hasBin: true
+
   sdp-transform@3.0.0:
     resolution: {integrity: sha512-gfYVRGxjHkGF2NPeUWHw5u6T/KGFtS5/drPms73gaSuMaVHKCY3lpLnGDfswVQO0kddeePoti09AwhYP4zA8dQ==}
     hasBin: true
 
+  sdp@3.2.2:
+    resolution: {integrity: sha512-xZocWwfyp4hkbN4hLWxMjmv2Q8aNa9MhmOZ7L9aCZPT+dZsgRr6wZRrSYE3HTdyk/2pZKPSgqI7ns7Een1xMSA==}
+
   source-map-js@1.2.2:
     resolution: {integrity: sha512-KGj/8Y43x35aZVDtt+J4mK1hoLGHULMYfSkODJNQjNDC3oW1PqPoxMwo0pLUsWM/UEGzON/NxeHywEfNXNP3Vw==}
     engines: {node: '>=0.10.0'}
@@ -845,6 +882,12 @@ packages:
     resolution: {integrity: sha512-wXR/dYpcqKmfWpEdZjiKJOwCNFndD0DMnrW/cYjVGttEkBfVgcLFHoNrlj47mjOVic9yyNu65alsgF4NQyTa2g==}
     engines: {node: '>=12.0.0'}
 
+  tslib@2.8.1:
+    resolution: {integrity: sha512-oJFu94HQb+KVduSUQL7wnpmqnfmLsOA/nAh6b6EH0wCEoK0/mPeXU6c3wKDV83MkOuHPRHtSXKKU99IBazS/2w==}
+
+  typed-emitter@2.1.0:
+    resolution: {integrity: sha512-g/KzbYKbH5C2vPkaXGu8DJlHrGKHLsM25Zg9WuC9pMGfuvT+X25tZQWo5fK1BjBm8+UrVE9LDCvaY0CQk+fXDA==}
+
   typescript@5.9.3:
     resolution: {integrity: sha512-jl1vZzPDinLr9eUt3J/t7V6FgNEw9QjvBPdysz9KfQDD41fQrC2Y4vKQdiaUpFT4bXlb1RHhLpp8wtm6M5TgSw==}
     engines: {node: '>=14.17'}
@@ -918,6 +961,10 @@ packages:
       typescript:
         optional: true
 
+  webrtc-adapter@9.0.6:
+    resolution: {integrity: sha512-CHbl2ZQbxx164IgWRgzJno4hWtM4tFbRam1QfI3Yxhs3w/DvqluVxVWeXs3oL5/fbGkSNLKo0Ty5MgUWceNhog==}
+    engines: {node: '>=6.0.0', npm: '>=3.10.0'}
+
 snapshots:
 
   '@babel/helper-string-parser@7.29.7': {}
@@ -935,6 +982,8 @@ snapshots:
       '@babel/helper-string-parser': 7.29.7
       '@babel/helper-validator-identifier': 7.29.7
 
+  '@bufbuild/protobuf@1.10.1': {}
+
   '@esbuild/aix-ppc64@0.28.2':
     optional: true
 
@@ -1032,6 +1081,12 @@ snapshots:
       '@jridgewell/resolve-uri': 3.1.2
       '@jridgewell/sourcemap-codec': 1.6.0
 
+  '@livekit/mutex@1.1.1': {}
+
+  '@livekit/protocol@1.50.4':
+    dependencies:
+      '@bufbuild/protobuf': 1.10.1
+
   '@matrix-org/matrix-sdk-crypto-wasm@18.9.0': {}
 
   '@napi-rs/lzma-linux-x64-gnu@1.5.1':
@@ -1182,6 +1237,8 @@ snapshots:
       tailwindcss: 4.3.3
       vite: 7.3.7(@types/node@22.20.5)(jiti@2.7.0)(lightningcss@1.32.0)
 
+  '@types/dom-mediacapture-record@1.0.22': {}
+
   '@types/estree@1.0.9': {}
 
   '@types/events@3.0.3': {}
@@ -1367,6 +1424,8 @@ snapshots:
 
   jiti@2.7.0: {}
 
+  jose@6.2.12: {}
+
   jsqr@1.4.0: {}
 
   lightningcss-android-arm64@1.32.0:
@@ -1418,8 +1477,24 @@ snapshots:
       lightningcss-win32-arm64-msvc: 1.32.0
       lightningcss-win32-x64-msvc: 1.32.0
 
+  livekit-client@2.22.3(@types/dom-mediacapture-record@1.0.22):
+    dependencies:
+      '@livekit/mutex': 1.1.1
+      '@livekit/protocol': 1.50.4
+      '@types/dom-mediacapture-record': 1.0.22
+      events: 3.3.0
+      jose: 6.2.12
+      loglevel: 1.9.2
+      machina: 7.0.1
+      sdp-transform: 2.15.0
+      tslib: 2.8.1
+      typed-emitter: 2.1.0
+      webrtc-adapter: 9.0.6
+
   loglevel@1.9.2: {}
 
+  machina@7.0.1: {}
+
   magic-string@0.30.21:
     dependencies:
       '@jridgewell/sourcemap-codec': 1.6.0
@@ -1512,8 +1587,17 @@ snapshots:
       '@rollup/rollup-win32-x64-msvc': 4.64.9
       fsevents: 2.3.3
 
+  rxjs@7.8.2:
+    dependencies:
+      tslib: 2.8.1
+    optional: true
+
+  sdp-transform@2.15.0: {}
+
   sdp-transform@3.0.0: {}
 
+  sdp@3.2.2: {}
+
   source-map-js@1.2.2: {}
 
   speakingurl@14.0.1: {}
@@ -1531,6 +1615,12 @@ snapshots:
       fdir: 6.5.0(picomatch@4.0.7)
       picomatch: 4.0.7
 
+  tslib@2.8.1: {}
+
+  typed-emitter@2.1.0:
+    optionalDependencies:
+      rxjs: 7.8.2
+
   typescript@5.9.3: {}
 
   undici-types@6.21.0: {}
@@ -1573,3 +1663,7 @@ snapshots:
       '@vue/shared': 3.5.44
     optionalDependencies:
       typescript: 5.9.3
+
+  webrtc-adapter@9.0.6:
+    dependencies:
+      sdp: 3.2.2
diff --git a/server/internal/clientapi/clientapi.go b/server/internal/clientapi/clientapi.go
index e802ac9..7708c13 100644
--- a/server/internal/clientapi/clientapi.go
+++ b/server/internal/clientapi/clientapi.go
@@ -19,6 +19,7 @@ import (
 
 	"github.com/dariuszjaniak/warp/server/internal/appservice"
 	"github.com/dariuszjaniak/warp/server/internal/config"
+	"github.com/dariuszjaniak/warp/server/internal/delayedevents"
 	"github.com/dariuszjaniak/warp/server/internal/federation"
 	"github.com/dariuszjaniak/warp/server/internal/httputil"
 	"github.com/dariuszjaniak/warp/server/internal/keyserver"
@@ -27,6 +28,7 @@ import (
 	"github.com/dariuszjaniak/warp/server/internal/ratelimit"
 	"github.com/dariuszjaniak/warp/server/internal/roomserver"
 	"github.com/dariuszjaniak/warp/server/internal/settings"
+	"github.com/dariuszjaniak/warp/server/internal/storage"
 	"github.com/dariuszjaniak/warp/server/internal/syncapi"
 	"github.com/dariuszjaniak/warp/server/internal/userapi"
 )
@@ -48,6 +50,9 @@ type ClientAPI struct {
 	regTokens     *userapi.RegistrationTokens
 	appservices   *appservice.API
 	turn          config.TURN
+	delayed       *delayedevents.Service
+	rtcTransports []RTCTransport
+	openID        storage.OpenIDTokenStore
 	log           *slog.Logger
 	now           func() time.Time
 
@@ -145,6 +150,20 @@ type Options struct {
 	// TURN is the relay handed to clients for calls.
 	TURN config.TURN
 
+	// RTC is the group call backend, listed at the MSC4143 transports
+	// endpoint.
+	RTC config.RTC
+
+	// DelayedEvents schedules MSC4140 delayed events. Nil, or a service
+	// with delayed events switched off, leaves the endpoints unregistered
+	// and refuses the delay parameter.
+	DelayedEvents *delayedevents.Service
+
+	// OpenIDTokens keeps the OpenID tokens a user hands third parties,
+	// such as the LiveKit JWT service of a group call. Nil leaves the
+	// OpenID endpoints unregistered.
+	OpenIDTokens storage.OpenIDTokenStore
+
 	// TrustXForwardedFor takes the client address from the proxy header.
 	TrustXForwardedFor bool
 
@@ -205,6 +224,9 @@ func New(opts Options) (*ClientAPI, error) {
 		regTokens:     opts.RegistrationTokens,
 		appservices:   opts.AppServices,
 		turn:          opts.TURN,
+		delayed:       opts.DelayedEvents,
+		rtcTransports: RTCTransports(opts.RTC.LiveKitServiceURL),
+		openID:        opts.OpenIDTokens,
 		log:           opts.Logger,
 		now:           opts.Now,
 		uia:           newUIAStore(uiaSessionTTL, opts.Now),
@@ -274,6 +296,9 @@ func (c *ClientAPI) RegisterRoutes(r *httputil.Router) {
 
 	// Calls: the relay a client sets its peer connection up with.
 	c.authed(r, "GET "+v3+"/voip/turnServer", c.limitDefault, c.handleTurnServer)
+	c.registerOpenIDRoutes(r)
+	c.registerDelayedEventRoutes(r)
+	c.registerRTCRoutes(r)
 
 	// Devices.
 	c.authed(r, "GET "+v3+"/devices", c.limitDefault, c.handleGetDevices)
diff --git a/server/internal/clientapi/clientapi_test.go b/server/internal/clientapi/clientapi_test.go
index 92b7fe8..d9e0828 100644
--- a/server/internal/clientapi/clientapi_test.go
+++ b/server/internal/clientapi/clientapi_test.go
@@ -2,16 +2,20 @@ package clientapi_test
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
 	"io"
 	"log/slog"
 	"net/http"
 	"net/http/httptest"
 	"path/filepath"
+	"sync"
 	"testing"
+	"time"
 
 	"github.com/dariuszjaniak/warp/server/internal/clientapi"
 	"github.com/dariuszjaniak/warp/server/internal/config"
+	"github.com/dariuszjaniak/warp/server/internal/delayedevents"
 	"github.com/dariuszjaniak/warp/server/internal/federation"
 	"github.com/dariuszjaniak/warp/server/internal/httputil"
 	"github.com/dariuszjaniak/warp/server/internal/matrix/signing"
@@ -39,6 +43,44 @@ type testServer struct {
 	settings *settings.Service
 	fedGate  *federation.Gate
 	db       storage.Database
+
+	// delayed is the delayed event service, on a clock of its own that
+	// tests move with advance.
+	delayed *delayedevents.Service
+	clock   *testClock
+}
+
+// testClock is a clock a test moves by hand.
+type testClock struct {
+	mu  sync.Mutex
+	now time.Time
+}
+
+func (c *testClock) Now() time.Time {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.now
+}
+
+func (c *testClock) advance(d time.Duration) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.now = c.now.Add(d)
+}
+
+// teeNotifier passes the roomserver's emit stage on to the syncapi and,
+// once it is built, to the delayed event service, which needs the
+// roomserver to exist first.
+type teeNotifier struct {
+	first roomserver.Notifier
+	then  roomserver.Notifier
+}
+
+func (n *teeNotifier) EventPersisted(ctx context.Context, note roomserver.Notification) {
+	n.first.EventPersisted(ctx, note)
+	if n.then != nil {
+		n.then.EventPersisted(ctx, note)
+	}
 }
 
 // newTestServer builds a server. tweak adjusts the options before the
@@ -91,13 +133,14 @@ func newTestServer(t *testing.T, tweak func(*clientapi.Options)) *testServer {
 	// stage and the syncapi's wake-up are the same object, exactly as in
 	// a real server.
 	notifier := syncapi.NewNotifier()
+	emit := &teeNotifier{first: notifier}
 	rooms, err := roomserver.New(roomserver.Options{
 		ServerName:        testServerName,
 		Store:             db.Rooms(),
 		Profiles:          users,
 		SigningKey:        key,
 		FederationEnabled: settingsService.FederationEnabled,
-		Notifier:          notifier,
+		Notifier:          emit,
 		Logger:            slog.New(slog.DiscardHandler),
 	})
 	if err != nil {
@@ -121,14 +164,34 @@ func newTestServer(t *testing.T, tweak func(*clientapi.Options)) *testServer {
 	}
 	t.Cleanup(sync.Close)
 
+	// Delayed events are on, with the scheduler left stopped: a test
+	// moves the clock and calls SendDue itself.
+	clock := &testClock{now: time.Now()}
+	delayed, err := delayedevents.New(delayedevents.Options{
+		Store:         db.DelayedEvents(),
+		Rooms:         rooms,
+		MaxDelay:      time.Hour,
+		MaxPerUser:    5,
+		DescribeError: clientapi.DescribeRoomError,
+		Logger:        slog.New(slog.DiscardHandler),
+		Now:           clock.Now,
+	})
+	if err != nil {
+		t.Fatalf("delayedevents.New: %v", err)
+	}
+	t.Cleanup(delayed.Close)
+	emit.then = delayed
+
 	opts := clientapi.Options{
-		ServerName: testServerName,
-		Users:      users,
-		Rooms:      rooms,
-		Sync:       sync,
-		Settings:   settingsService,
-		Federation: gate,
-		Logger:     slog.New(slog.DiscardHandler),
+		ServerName:    testServerName,
+		Users:         users,
+		Rooms:         rooms,
+		Sync:          sync,
+		Settings:      settingsService,
+		Federation:    gate,
+		DelayedEvents: delayed,
+		OpenIDTokens:  db.OpenIDTokens(),
+		Logger:        slog.New(slog.DiscardHandler),
 	}
 	if tweak != nil {
 		tweak(&opts)
@@ -150,6 +213,8 @@ func newTestServer(t *testing.T, tweak func(*clientapi.Options)) *testServer {
 		settings: settingsService,
 		fedGate:  gate,
 		db:       db,
+		delayed:  delayed,
+		clock:    clock,
 	}
 }
 
diff --git a/server/internal/clientapi/delayed.go b/server/internal/clientapi/delayed.go
new file mode 100644
index 0000000..47dd0c5
--- /dev/null
+++ b/server/internal/clientapi/delayed.go
@@ -0,0 +1,259 @@
+package clientapi
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+	"slices"
+	"strconv"
+	"time"
+
+	"github.com/dariuszjaniak/warp/server/internal/delayedevents"
+	"github.com/dariuszjaniak/warp/server/internal/httputil"
+	"github.com/dariuszjaniak/warp/server/internal/roomserver"
+	"github.com/dariuszjaniak/warp/server/internal/storage"
+	"github.com/dariuszjaniak/warp/server/internal/userapi"
+)
+
+// MSC4140 is still unstable, so its endpoints and parameters carry its
+// prefix.
+const (
+	delayedEventsPrefix = "/_matrix/client/unstable/org.matrix.msc4140"
+	delayParam          = "org.matrix.msc4140.delay"
+	parentDelayParam    = "org.matrix.msc4140.parent_delay_id"
+)
+
+// registerDelayedEventRoutes adds the MSC4140 endpoints, if delayed events
+// are switched on.
+//
+// The action endpoints are public: the delay ID is the capability, which is
+// what lets a client hand its delayed leave to something else to keep alive.
+// Both spellings are served — the action in the path, which is the current
+// draft, and in the body, which clients fall back to.
+func (c *ClientAPI) registerDelayedEventRoutes(r *httputil.Router) {
+	if !c.delayed.Enabled() || c.rooms == nil {
+		return
+	}
+	c.authed(r, "GET "+delayedEventsPrefix+"/delayed_events", c.limitDefault, c.handleGetDelayedEvents)
+	c.authed(r, "GET "+delayedEventsPrefix+"/delayed_events/{delayID}", c.limitDefault, c.handleGetDelayedEvent)
+	c.public(r, "POST "+delayedEventsPrefix+"/delayed_events/{delayID}", c.limitDefault, c.handleUpdateDelayedEvent)
+	c.public(r, "POST "+delayedEventsPrefix+"/delayed_events/{delayID}/{action}", c.limitDefault, c.handleUpdateDelayedEvent)
+}
+
+// delayRequested reads the delay parameter of a send or state PUT. ok is
+// false when there is none, and the event is sent at once as usual.
+func (c *ClientAPI) delayRequested(r *http.Request) (time.Duration, bool, error) {
+	q := r.URL.Query()
+	if q.Has(parentDelayParam) {
+		return 0, false, httputil.InvalidParam("%s is not supported", parentDelayParam)
+	}
+	if !q.Has(delayParam) {
+		return 0, false, nil
+	}
+	if !c.delayed.Enabled() {
+		// Refused rather than ignored: sending a delayed "left the call"
+		// at once would be exactly the wrong thing.
+		return 0, false, httputil.InvalidParam("Delayed events are not enabled on this server")
+	}
+	ms, err := strconv.ParseInt(q.Get(delayParam), 10, 64)
+	if err != nil || ms < 0 {
+		return 0, false, httputil.InvalidParam("%s must be a non-negative number of milliseconds", delayParam)
+	}
+	return time.Duration(ms) * time.Millisecond, true, nil
+}
+
+// delayIDResponse answers a delayed send.
+type delayIDResponse struct {
+	DelayID string `json:"delay_id"`
+}
+
+// scheduleDelayed schedules what a send or state PUT asked to delay.
+func (c *ClientAPI) scheduleDelayed(w http.ResponseWriter, r *http.Request, req delayedevents.ScheduleRequest) error {
+	delayID, err := c.delayed.Schedule(r.Context(), req)
+	if err != nil {
+		return delayedError(err, c.delayed.MaxDelay())
+	}
+	httputil.WriteJSON(w, http.StatusOK, delayIDResponse{DelayID: delayID})
+	return nil
+}
+
+// delayedError maps the service's errors onto Matrix errors. An overlong
+// delay is reported the way Synapse does: M_UNKNOWN for a client that knows
+// nothing of MSC4140, with the MSC's own code and the maximum alongside.
+func delayedError(err error, maxDelay time.Duration) error {
+	switch {
+	case errors.Is(err, delayedevents.ErrMaxDelayExceeded):
+		merr := httputil.NewError(http.StatusBadRequest, httputil.ErrCodeUnknown, "%s", err.Error())
+		merr.DelayedErrCode = "M_MAX_DELAY_EXCEEDED"
+		merr.MaxDelayMS = maxDelay.Milliseconds()
+		return merr
+	case errors.Is(err, delayedevents.ErrTooMany):
+		return httputil.NewError(http.StatusBadRequest, "M_LIMIT_EXCEEDED", "%s", err.Error())
+	case errors.Is(err, delayedevents.ErrDisabled):
+		return httputil.Unrecognized()
+	case errors.Is(err, storage.ErrNoSuchDelayedEvent):
+		return httputil.NotFound("No such scheduled delayed event")
+	default:
+		return roomError(err)
+	}
+}
+
+// delayedEventJSON is one delayed event as MSC4140 lists it.
+type delayedEventJSON struct {
+	DelayID      string          `json:"delay_id"`
+	RoomID       string          `json:"room_id"`
+	Type         string          `json:"type"`
+	StateKey     *string         `json:"state_key,omitempty"`
+	Content      json.RawMessage `json:"content"`
+	Delay        int64           `json:"delay"`
+	RunningSince int64           `json:"running_since"`
+}
+
+type finalisedDelayedEventJSON struct {
+	DelayedEvent   delayedEventJSON `json:"delayed_event"`
+	Outcome        string           `json:"outcome"`
+	Reason         string           `json:"reason"`
+	Error          json.RawMessage  `json:"error,omitempty"`
+	EventID        string           `json:"event_id,omitempty"`
+	OriginServerTS int64            `json:"origin_server_ts,omitempty"`
+}
+
+type delayedEventsResponse struct {
+	Scheduled []delayedEventJSON          `json:"scheduled"`
+	Finalised []finalisedDelayedEventJSON `json:"finalised"`
+
+	// DelayedEvents is the scheduled list under the name an earlier draft
+	// of MSC4140 used.
+	DelayedEvents []delayedEventJSON `json:"delayed_events"`
+}
+
+func toDelayedEventJSON(e storage.DelayedEvent) delayedEventJSON {
+	return delayedEventJSON{
+		DelayID:      e.DelayID,
+		RoomID:       e.RoomID,
+		Type:         e.Type,
+		StateKey:     e.StateKey,
+		Content:      e.Content,
+		Delay:        e.DelayMS,
+		RunningSince: e.RunningSinceMS,
+	}
+}
+
+func toFinalisedJSON(e storage.DelayedEvent) finalisedDelayedEventJSON {
+	out := finalisedDelayedEventJSON{
+		DelayedEvent: toDelayedEventJSON(e),
+		Outcome:      e.Outcome,
+		Reason:       e.Reason,
+		Error:        e.Error,
+		EventID:      e.EventID,
+	}
+	if e.EventID != "" {
+		out.OriginServerTS = e.FinalisedAtMS
+	}
+	return out
+}
+
+// handleGetDelayedEvents implements
+// GET /_matrix/client/unstable/org.matrix.msc4140/delayed_events.
+//
+// status narrows the answer to scheduled or finalised events, and delay_id,
+// which may repeat, to particular ones. Nobody has enough delayed events
+// for paging to matter, so there is never a next_batch.
+func (c *ClientAPI) handleGetDelayedEvents(w http.ResponseWriter, r *http.Request, auth userapi.Authenticated) error {
+	q := r.URL.Query()
+	status := q.Get("status")
+	if status != "" && status != "scheduled" && status != "finalised" {
+		return httputil.InvalidParam("status must be scheduled or finalised")
+	}
+	ids := q["delay_id"]
+
+	events, err := c.delayed.List(r.Context(), auth.UserID)
+	if err != nil {
+		return err
+	}
+	resp := delayedEventsResponse{
+		Scheduled: []delayedEventJSON{},
+		Finalised: []finalisedDelayedEventJSON{},
+	}
+	for _, e := range events {
+		if len(ids) > 0 && !slices.Contains(ids, e.DelayID) {
+			continue
+		}
+		if e.FinalisedAtMS == 0 {
+			if status != "finalised" {
+				resp.Scheduled = append(resp.Scheduled, toDelayedEventJSON(e))
+			}
+		} else if status != "scheduled" {
+			resp.Finalised = append(resp.Finalised, toFinalisedJSON(e))
+		}
+	}
+	resp.DelayedEvents = resp.Scheduled
+	httputil.WriteJSON(w, http.StatusOK, resp)
+	return nil
+}
+
+// handleGetDelayedEvent implements
+// GET /_matrix/client/unstable/org.matrix.msc4140/delayed_events/{delayID}.
+func (c *ClientAPI) handleGetDelayedEvent(w http.ResponseWriter, r *http.Request, auth userapi.Authenticated) error {
+	e, err := c.delayed.Get(r.Context(), auth.UserID, r.PathValue("delayID"))
+	if err != nil {
+		return delayedError(err, 0)
+	}
+	if e.FinalisedAtMS == 0 {
+		httputil.WriteJSON(w, http.StatusOK, toDelayedEventJSON(e))
+	} else {
+		httputil.WriteJSON(w, http.StatusOK, toFinalisedJSON(e))
+	}
+	return nil
+}
+
+type updateDelayedEventRequest struct {
+	Action string `json:"action"`
+}
+
+// handleUpdateDelayedEvent implements
+// POST /_matrix/client/unstable/org.matrix.msc4140/delayed_events/{delayID}[/{action}].
+func (c *ClientAPI) handleUpdateDelayedEvent(w http.ResponseWriter, r *http.Request) error {
+	delayID := r.PathValue("delayID")
+	action := r.PathValue("action")
+	if action == "" {
+		var req updateDelayedEventRequest
+		if err := httputil.DecodeJSON(w, r, &req); err != nil {
+			return err
+		}
+		action = req.Action
+	}
+
+	var err error
+	switch action {
+	case "restart":
+		err = c.delayed.Restart(r.Context(), delayID)
+	case "cancel":
+		err = c.delayed.Cancel(r.Context(), delayID)
+	case "send":
+		err = c.delayed.Send(r.Context(), delayID)
+	case "":
+		return httputil.MissingParam("An action is required")
+	default:
+		return httputil.InvalidParam("action must be restart, cancel or send")
+	}
+	if err != nil {
+		return delayedError(err, 0)
+	}
+	httputil.WriteJSON(w, http.StatusOK, struct{}{})
+	return nil
+}
+
+// DescribeRoomError is the Matrix error a failed delayed send is recorded
+// with: the error the client would have got had it sent the event itself.
+func DescribeRoomError(err error) json.RawMessage {
+	var matrixErr *httputil.MatrixError
+	if !errors.As(roomError(err), &matrixErr) {
+		matrixErr = httputil.NewError(http.StatusInternalServerError, httputil.ErrCodeUnknown, "%s", err.Error())
+	}
+	raw, _ := json.Marshal(matrixErr)
+	return raw
+}
+
+// Compile-time check that the roomserver can be the service's sender.
+var _ delayedevents.Sender = (*roomserver.API)(nil)
diff --git a/server/internal/clientapi/delayed_test.go b/server/internal/clientapi/delayed_test.go
new file mode 100644
index 0000000..b23da27
--- /dev/null
+++ b/server/internal/clientapi/delayed_test.go
@@ -0,0 +1,300 @@
+package clientapi_test
+
+import (
+	"net/http"
+	"net/url"
+	"strconv"
+	"testing"
+	"time"
+
+	"github.com/dariuszjaniak/warp/server/internal/clientapi"
+	"github.com/dariuszjaniak/warp/server/internal/httputil"
+)
+
+const delayedEventsPath = "/_matrix/client/unstable/org.matrix.msc4140/delayed_events"
+
+// callMemberPath is where a member of a room's group call puts its state.
+func callMemberPath(roomID, stateKey string) string {
+	return "/_matrix/client/v3/rooms/" + url.PathEscape(roomID) +
+		"/state/org.matrix.msc3401.call.member/" + url.PathEscape(stateKey)
+}
+
+// scheduleDelayed PUTs a delayed state event and returns its delay ID.
+func (ts *testServer) scheduleDelayed(path string, delayMS int, acc account, content map[string]any) string {
+	ts.t.Helper()
+	rec := ts.put(path+"?org.matrix.msc4140.delay="+strconv.Itoa(delayMS), acc.AccessToken, content)
+	expectStatus(ts.t, rec, http.StatusOK)
+	delayID, _ := jsonBody(ts.t, rec)["delay_id"].(string)
+	if delayID == "" {
+		ts.t.Fatalf("a delayed send returned no delay_id: %s", rec.Body.String())
+	}
+	return delayID
+}
+
+// tick moves the clock and sends whatever has come due.
+func (ts *testServer) tick(d time.Duration) {
+	ts.t.Helper()
+	ts.clock.advance(d)
+	ts.delayed.SendDue(ts.t.Context())
+}
+
+type delayedList struct {
+	Scheduled []struct {
+		DelayID      string         `json:"delay_id"`
+		RoomID       string         `json:"room_id"`
+		Type         string         `json:"type"`
+		StateKey     *string        `json:"state_key"`
+		Content      map[string]any `json:"content"`
+		Delay        int64          `json:"delay"`
+		RunningSince int64          `json:"running_since"`
+	} `json:"scheduled"`
+	Finalised []struct {
+		DelayedEvent struct {
+			DelayID string `json:"delay_id"`
+		} `json:"delayed_event"`
+		Outcome string         `json:"outcome"`
+		Reason  string         `json:"reason"`
+		EventID string         `json:"event_id"`
+		Error   map[string]any `json:"error"`
+	} `json:"finalised"`
+}
+
+func (ts *testServer) delayedList(acc account) delayedList {
+	ts.t.Helper()
+	rec := ts.get(delayedEventsPath, acc.AccessToken)
+	expectStatus(ts.t, rec, http.StatusOK)
+	return decode[delayedList](ts.t, rec)
+}
+
+// TestDelayedStateEventIsSentWhenDue is the MatrixRTC case: a member's
+// "left the call" is scheduled when it joins, and arrives on its own once
+// the delay runs out.
+func TestDelayedStateEventIsSentWhenDue(t *testing.T) {
+	ts := newTestServer(t, nil)
+	alice := ts.register("alice", "correct-horse-battery-staple")
+	roomID := ts.createRoom(alice, map[string]any{"preset": "public_chat"})
+	stateKey := "_" + alice.UserID + "_" + alice.DeviceID + "_m.call"
+	path := callMemberPath(roomID, stateKey)
+
+	delayID := ts.scheduleDelayed(path, 5000, alice, map[string]any{})
+
+	// Nothing is in the room yet.
+	expectError(t, ts.get(path, alice.AccessToken), http.StatusNotFound, httputil.ErrCodeNotFound)
+
+	list := ts.delayedList(alice)
+	if len(list.Scheduled) != 1 || list.Scheduled[0].DelayID != delayID {
+		t.Fatalf("scheduled = %+v", list.Scheduled)
+	}
+	got := list.Scheduled[0]
+	if got.RoomID != roomID || got.Type != "org.matrix.msc3401.call.member" ||
+		got.StateKey == nil || *got.StateKey != stateKey || got.Delay != 5000 {
+		t.Errorf("the scheduled event is %+v", got)
+	}
+
+	ts.tick(4 * time.Second)
+	expectError(t, ts.get(path, alice.AccessToken), http.StatusNotFound, httputil.ErrCodeNotFound)
+
+	ts.tick(2 * time.Second)
+	expectStatus(t, ts.get(path, alice.AccessToken), http.StatusOK)
+
+	list = ts.delayedList(alice)
+	if len(list.Scheduled) != 0 {
+		t.Errorf("still scheduled after sending: %+v", list.Scheduled)
+	}
+	if len(list.Finalised) != 1 || list.Finalised[0].Outcome != "send" ||
+		list.Finalised[0].Reason != "delay" || list.Finalised[0].EventID == "" {
+		t.Errorf("finalised = %+v", list.Finalised)
+	}
+
+	// Looked up on its own, it is the same.
+	rec := ts.get(delayedEventsPath+"/"+delayID, alice.AccessToken)
+	expectStatus(t, rec, http.StatusOK)
+	if jsonBody(t, rec)["outcome"] != "send" {
+		t.Errorf("GET by ID = %s", rec.Body.String())
+	}
+}
+
+// TestDelayedEventRestart: a client still in the call keeps pushing its
+// leave back, and it never arrives.
+func TestDelayedEventRestart(t *testing.T) {
+	ts := newTestServer(t, nil)
+	alice := ts.register("alice", "correct-horse-battery-staple")
+	roomID := ts.createRoom(alice, map[string]any{"preset": "public_chat"})
+	path := callMemberPath(roomID, "_"+alice.UserID+"_D_m.call")
+
+	delayID := ts.scheduleDelayed(path, 5000, alice, map[string]any{})
+
+	for range 3 {
+		ts.tick(4 * time.Second)
+		// The action endpoints need no token: the delay ID is the
+		// capability.
+		expectStatus(t, ts.post(delayedEventsPath+"/"+delayID+"/restart", "", nil), http.StatusOK)
+	}
+	ts.tick(4 * time.Second)
+	expectError(t, ts.get(path, alice.AccessToken), http.StatusNotFound, httputil.ErrCodeNotFound)
+
+	ts.tick(2 * time.Second)
+	expectStatus(t, ts.get(path, alice.AccessToken), http.StatusOK)
+
+	// Once it has been sent it cannot be restarted.
+	rec := ts.post(delayedEventsPath+"/"+delayID+"/restart", "", nil)
+	expectError(t, rec, http.StatusNotFound, httputil.ErrCodeNotFound)
+}
+
+// TestDelayedEventActions covers cancel and send, in both the path and the
+// body spelling.
+func TestDelayedEventActions(t *testing.T) {
+	ts := newTestServer(t, nil)
+	alice := ts.register("alice", "correct-horse-battery-staple")
+	roomID := ts.createRoom(alice, map[string]any{"preset": "public_chat"})
+	escaped := url.PathEscape(roomID)
+
+	// Cancelled with the action in the body: never sent.
+	topic := "/_matrix/client/v3/rooms/" + escaped + "/state/m.room.topic"
+	cancelled := ts.scheduleDelayed(topic, 1000, alice, map[string]any{"topic": "never"})
+	expectStatus(t, ts.post(delayedEventsPath+"/"+cancelled, alice.AccessToken,
+		map[string]any{"action": "cancel"}), http.StatusOK)
+	ts.tick(2 * time.Second)
+	expectError(t, ts.get(topic, alice.AccessToken), http.StatusNotFound, httputil.ErrCodeNotFound)
+
+	// Sent at once with the action in the path: a timeline event, which
+	// is how a client sends a message it held back.
+	send := "/_matrix/client/v3/rooms/" + escaped + "/send/m.room.message/txn1"
+	sent := ts.scheduleDelayed(send, 60000, alice, map[string]any{"msgtype": "m.text", "body": "later"})
+	expectStatus(t, ts.post(delayedEventsPath+"/"+sent+"/send", "", nil), http.StatusOK)
+
+	list := ts.delayedList(alice)
+	if len(list.Scheduled) != 0 || len(list.Finalised) != 2 {
+		t.Fatalf("list = %+v", list)
+	}
+	outcomes := map[string]string{}
+	for _, f := range list.Finalised {
+		outcomes[f.DelayedEvent.DelayID] = f.Outcome + "/" + f.Reason
+	}
+	if outcomes[cancelled] != "cancel/action" || outcomes[sent] != "send/action" {
+		t.Errorf("outcomes = %v", outcomes)
+	}
+
+	// status narrows the list.
+	rec := ts.get(delayedEventsPath+"?status=scheduled", alice.AccessToken)
+	expectStatus(t, rec, http.StatusOK)
+	if l := decode[delayedList](t, rec); len(l.Finalised) != 0 {
+		t.Errorf("status=scheduled listed finalised events: %s", rec.Body.String())
+	}
+
+	expectError(t, ts.post(delayedEventsPath+"/nope/cancel", "", nil), http.StatusNotFound, httputil.ErrCodeNotFound)
+	expectError(t, ts.post(delayedEventsPath+"/"+sent+"/explode", "", nil),
+		http.StatusBadRequest, httputil.ErrCodeInvalidParam)
+}
+
+// TestDelayedEventFailureIsRecorded: an event that can no longer be sent
+// is finalised with the error the client would have got.
+func TestDelayedEventFailureIsRecorded(t *testing.T) {
+	ts := newTestServer(t, nil)
+	alice := ts.register("alice", "correct-horse-battery-staple")
+	roomID := ts.createRoom(alice, map[string]any{"preset": "public_chat"})
+	path := callMemberPath(roomID, "_"+alice.UserID+"_D_m.call")
+
+	ts.scheduleDelayed(path, 1000, alice, map[string]any{})
+	expectStatus(t, ts.post("/_matrix/client/v3/rooms/"+url.PathEscape(roomID)+"/leave",
+		alice.AccessToken, map[string]any{}), http.StatusOK)
+	ts.tick(2 * time.Second)
+
+	list := ts.delayedList(alice)
+	if len(list.Finalised) != 1 || list.Finalised[0].Reason != "error" ||
+		list.Finalised[0].Error["errcode"] != httputil.ErrCodeForbidden {
+		t.Errorf("finalised = %+v", list.Finalised)
+	}
+}
+
+// TestDelayedStateIsCancelledByOthers: someone else setting the same state
+// cancels a delayed event that would have overwritten it, and the owner's
+// own updates do not. It also proves an ordinary member may join a call.
+func TestDelayedStateIsCancelledByOthers(t *testing.T) {
+	ts := newTestServer(t, nil)
+	alice := ts.register("alice", "correct-horse-battery-staple")
+	bob := ts.register("bob", "correct-horse-battery-staple")
+	roomID := ts.createRoom(alice, map[string]any{"preset": "public_chat"})
+	expectStatus(t, ts.post("/_matrix/client/v3/rooms/"+url.PathEscape(roomID)+"/join",
+		bob.AccessToken, map[string]any{}), http.StatusOK)
+
+	aliceKey := callMemberPath(roomID, "_"+alice.UserID+"_A_m.call")
+	ts.scheduleDelayed(aliceKey, 5000, alice, map[string]any{})
+
+	// Alice refreshing her own membership leaves the delayed leave alone.
+	expectStatus(t, ts.put(aliceKey, alice.AccessToken, map[string]any{"application": "m.call"}), http.StatusOK)
+	// Bob, an ordinary member, may put call state of his own.
+	expectStatus(t, ts.put(callMemberPath(roomID, "_"+bob.UserID+"_B_m.call"), bob.AccessToken,
+		map[string]any{"application": "m.call"}), http.StatusOK)
+	// The cancellation runs off the emit stage, so give it a moment.
+	time.Sleep(100 * time.Millisecond)
+	if l := ts.delayedList(alice); len(l.Scheduled) != 1 {
+		t.Fatalf("alice's own update cancelled her delayed event: %+v", l)
+	}
+
+	// Bob writing the same piece of state cancels it.
+	expectStatus(t, ts.put(aliceKey, bob.AccessToken, map[string]any{}), http.StatusOK)
+	deadline := time.Now().Add(5 * time.Second)
+	for {
+		l := ts.delayedList(alice)
+		if len(l.Scheduled) == 0 {
+			if len(l.Finalised) != 1 || l.Finalised[0].Outcome != "cancel" {
+				t.Errorf("finalised = %+v", l.Finalised)
+			}
+			break
+		}
+		if time.Now().After(deadline) {
+			t.Fatal("the overwritten delayed event was never cancelled")
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+}
+
+func TestDelayedEventLimits(t *testing.T) {
+	ts := newTestServer(t, nil)
+	alice := ts.register("alice", "correct-horse-battery-staple")
+	roomID := ts.createRoom(alice, map[string]any{"preset": "public_chat"})
+	topic := "/_matrix/client/v3/rooms/" + url.PathEscape(roomID) + "/state/m.room.topic"
+
+	// Longer than the server allows: the MSC's own code and the maximum
+	// come with the error.
+	rec := ts.put(topic+"?org.matrix.msc4140.delay=7200000", alice.AccessToken, map[string]any{"topic": "x"})
+	expectError(t, rec, http.StatusBadRequest, httputil.ErrCodeUnknown)
+	body := jsonBody(t, rec)
+	if body["org.matrix.msc4140.errcode"] != "M_MAX_DELAY_EXCEEDED" || body["org.matrix.msc4140.max_delay"] != float64(3600000) {
+		t.Errorf("error = %s", rec.Body.String())
+	}
+
+	expectError(t, ts.put(topic+"?org.matrix.msc4140.delay=soon", alice.AccessToken, map[string]any{"topic": "x"}),
+		http.StatusBadRequest, httputil.ErrCodeInvalidParam)
+	expectError(t, ts.put(topic+"?org.matrix.msc4140.parent_delay_id=x", alice.AccessToken, map[string]any{"topic": "x"}),
+		http.StatusBadRequest, httputil.ErrCodeInvalidParam)
+
+	// Five at once is the test server's limit.
+	for range 5 {
+		ts.scheduleDelayed(topic, 1000, alice, map[string]any{"topic": "x"})
+	}
+	rec = ts.put(topic+"?org.matrix.msc4140.delay=1000", alice.AccessToken, map[string]any{"topic": "x"})
+	expectError(t, rec, http.StatusBadRequest, "M_LIMIT_EXCEEDED")
+
+	// Nobody else can read them.
+	bob := ts.register("bob", "correct-horse-battery-staple")
+	if l := ts.delayedList(bob); len(l.Scheduled) != 0 {
+		t.Errorf("bob sees alice's delayed events: %+v", l)
+	}
+	expectError(t, ts.get(delayedEventsPath, ""), http.StatusUnauthorized, "M_MISSING_TOKEN")
+}
+
+// TestDelayedEventsDisabled: without the service the parameter is refused,
+// rather than the event being sent at once, and the endpoints are absent.
+func TestDelayedEventsDisabled(t *testing.T) {
+	ts := newTestServer(t, func(o *clientapi.Options) { o.DelayedEvents = nil })
+	alice := ts.register("alice", "correct-horse-battery-staple")
+	roomID := ts.createRoom(alice, map[string]any{"preset": "public_chat"})
+	path := callMemberPath(roomID, "_"+alice.UserID+"_A_m.call")
+
+	expectError(t, ts.put(path+"?org.matrix.msc4140.delay=1000", alice.AccessToken, map[string]any{}),
+		http.StatusBadRequest, httputil.ErrCodeInvalidParam)
+	expectError(t, ts.get(path, alice.AccessToken), http.StatusNotFound, httputil.ErrCodeNotFound)
+	expectError(t, ts.get(delayedEventsPath, alice.AccessToken), http.StatusNotFound, httputil.ErrCodeUnrecognized)
+}
diff --git a/server/internal/clientapi/openid.go b/server/internal/clientapi/openid.go
new file mode 100644
index 0000000..b2497a6
--- /dev/null
+++ b/server/internal/clientapi/openid.go
@@ -0,0 +1,106 @@
+package clientapi
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/dariuszjaniak/warp/server/internal/httputil"
+	"github.com/dariuszjaniak/warp/server/internal/storage"
+	"github.com/dariuszjaniak/warp/server/internal/userapi"
+)
+
+// openIDTokenLifetime is how long an OpenID token is good for. The LiveKit
+// JWT service checks it once, when a call is joined, so an hour is plenty.
+const openIDTokenLifetime = time.Hour
+
+// openIDTokenPrefix marks OpenID tokens the way the userapi marks access
+// tokens, so one handed to the wrong endpoint is recognisable.
+const openIDTokenPrefix = "warp_oi_"
+
+// openIDUserInfoPath is where a third party exchanges an OpenID token for
+// the user's ID. It is a federation endpoint by name, but needs neither
+// federation nor a signing key: Synapse serves it as a resource of its own
+// for the same reason. It is registered here so that a server with
+// federation off can still let its users into a group call.
+const openIDUserInfoPath = "/_matrix/federation/v1/openid/userinfo"
+
+// registerOpenIDRoutes adds the OpenID endpoints, if there is a store for
+// the tokens.
+func (c *ClientAPI) registerOpenIDRoutes(r *httputil.Router) {
+	if c.openID == nil {
+		return
+	}
+	c.authed(r, "POST "+v3+"/user/{userID}/openid/request_token", c.limitDefault, c.handleRequestOpenIDToken)
+	c.public(r, "GET "+openIDUserInfoPath, c.limitDefault, c.handleOpenIDUserInfo)
+}
+
+type openIDTokenResponse struct {
+	AccessToken      string `json:"access_token"`
+	TokenType        string `json:"token_type"`
+	MatrixServerName string `json:"matrix_server_name"`
+	ExpiresIn        int64  `json:"expires_in"`
+}
+
+// handleRequestOpenIDToken implements
+// POST /_matrix/client/v3/user/{userID}/openid/request_token.
+//
+// The token proves who the user is to whoever they hand it to, and nothing
+// else: it is not an access token and opens no other endpoint.
+func (c *ClientAPI) handleRequestOpenIDToken(w http.ResponseWriter, r *http.Request, auth userapi.Authenticated) error {
+	if r.PathValue("userID") != auth.UserID {
+		return httputil.Forbidden("You cannot request an OpenID token for another user")
+	}
+	// The body is an empty object; anything in it is ignored.
+	var ignored map[string]any
+	if _, err := httputil.DecodeOptionalJSON(w, r, &ignored); err != nil {
+		return err
+	}
+
+	raw := make([]byte, 32)
+	if _, err := rand.Read(raw); err != nil {
+		return fmt.Errorf("generate OpenID token: %w", err)
+	}
+	token := openIDTokenPrefix + base64.RawURLEncoding.EncodeToString(raw)
+	now := c.now()
+	// Expired tokens go as new ones are made; nothing else reads them.
+	if err := c.openID.PurgeOpenIDTokens(r.Context(), now.UnixMilli()); err != nil {
+		c.log.Warn("could not purge expired OpenID tokens", "error", err)
+	}
+	if err := c.openID.InsertOpenIDToken(r.Context(), userapi.HashToken(token), auth.UserID,
+		now.Add(openIDTokenLifetime).UnixMilli()); err != nil {
+		return err
+	}
+	httputil.WriteJSON(w, http.StatusOK, openIDTokenResponse{
+		AccessToken:      token,
+		TokenType:        "Bearer",
+		MatrixServerName: c.serverName,
+		ExpiresIn:        int64(openIDTokenLifetime.Seconds()),
+	})
+	return nil
+}
+
+type openIDUserInfoResponse struct {
+	Sub string `json:"sub"`
+}
+
+// handleOpenIDUserInfo implements
+// GET /_matrix/federation/v1/openid/userinfo.
+func (c *ClientAPI) handleOpenIDUserInfo(w http.ResponseWriter, r *http.Request) error {
+	token := r.URL.Query().Get("access_token")
+	if token == "" {
+		return httputil.MissingToken()
+	}
+	userID, err := c.openID.OpenIDTokenUser(r.Context(), userapi.HashToken(token), c.now().UnixMilli())
+	if errors.Is(err, storage.ErrNoSuchOpenIDToken) {
+		return httputil.UnknownToken(false)
+	}
+	if err != nil {
+		return err
+	}
+	httputil.WriteJSON(w, http.StatusOK, openIDUserInfoResponse{Sub: userID})
+	return nil
+}
diff --git a/server/internal/clientapi/openid_test.go b/server/internal/clientapi/openid_test.go
new file mode 100644
index 0000000..5ec3ac5
--- /dev/null
+++ b/server/internal/clientapi/openid_test.go
@@ -0,0 +1,61 @@
+package clientapi_test
+
+import (
+	"net/http"
+	"net/url"
+	"testing"
+
+	"github.com/dariuszjaniak/warp/server/internal/httputil"
+)
+
+// TestOpenIDToken is the exchange the LiveKit JWT service relies on: a user
+// asks for a token, hands it over, and the service asks this server who it
+// belongs to.
+func TestOpenIDToken(t *testing.T) {
+	ts := newTestServer(t, nil)
+	alice := ts.register("alice", "correct-horse-battery-staple")
+	bob := ts.register("bob", "correct-horse-battery-staple")
+	path := "/_matrix/client/v3/user/" + url.PathEscape(alice.UserID) + "/openid/request_token"
+
+	rec := ts.post(path, alice.AccessToken, map[string]any{})
+	expectStatus(t, rec, http.StatusOK)
+	body := jsonBody(t, rec)
+	token, _ := body["access_token"].(string)
+	if token == "" || body["token_type"] != "Bearer" || body["matrix_server_name"] != testServerName ||
+		body["expires_in"] != float64(3600) {
+		t.Fatalf("request_token = %s", rec.Body.String())
+	}
+
+	// The token is no access token.
+	expectError(t, ts.get("/_matrix/client/v3/account/whoami", token), http.StatusUnauthorized, httputil.ErrCodeUnknownToken)
+
+	rec = ts.get("/_matrix/federation/v1/openid/userinfo?access_token="+url.QueryEscape(token), "")
+	expectStatus(t, rec, http.StatusOK)
+	if got := jsonBody(t, rec)["sub"]; got != alice.UserID {
+		t.Errorf("sub = %v, want %s", got, alice.UserID)
+	}
+
+	expectError(t, ts.get("/_matrix/federation/v1/openid/userinfo?access_token=nope", ""),
+		http.StatusUnauthorized, httputil.ErrCodeUnknownToken)
+	expectError(t, ts.get("/_matrix/federation/v1/openid/userinfo", ""),
+		http.StatusUnauthorized, "M_MISSING_TOKEN")
+
+	// Nobody gets a token in someone else's name.
+	expectError(t, ts.post(path, bob.AccessToken, map[string]any{}), http.StatusForbidden, httputil.ErrCodeForbidden)
+}
+
+// TestOpenIDUserInfoIgnoresFederationSwitch: the userinfo endpoint answers
+// with federation off, so a server that does not federate can still let its
+// users into group calls.
+func TestOpenIDUserInfoIgnoresFederationSwitch(t *testing.T) {
+	ts := newTestServer(t, nil)
+	if ts.settings.FederationEnabled() {
+		t.Fatal("the test server is expected to start with federation off")
+	}
+	alice := ts.register("alice", "correct-horse-battery-staple")
+	rec := ts.post("/_matrix/client/v3/user/"+url.PathEscape(alice.UserID)+"/openid/request_token",
+		alice.AccessToken, nil)
+	expectStatus(t, rec, http.StatusOK)
+	token, _ := jsonBody(t, rec)["access_token"].(string)
+	expectStatus(t, ts.get("/_matrix/federation/v1/openid/userinfo?access_token="+url.QueryEscape(token), ""), http.StatusOK)
+}
diff --git a/server/internal/clientapi/rooms.go b/server/internal/clientapi/rooms.go
index 26c6b2f..72b3ec8 100644
--- a/server/internal/clientapi/rooms.go
+++ b/server/internal/clientapi/rooms.go
@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"strings"
 
+	"github.com/dariuszjaniak/warp/server/internal/delayedevents"
 	"github.com/dariuszjaniak/warp/server/internal/httputil"
 	"github.com/dariuszjaniak/warp/server/internal/matrix/id"
 	"github.com/dariuszjaniak/warp/server/internal/roomserver"
@@ -155,10 +156,20 @@ func (c *ClientAPI) handleSendEvent(w http.ResponseWriter, r *http.Request, auth
 		return httputil.MissingParam("A transaction ID is required")
 	}
 
+	delay, delayed, err := c.delayRequested(r)
+	if err != nil {
+		return err
+	}
 	var content sendEventRequest
 	if err := httputil.DecodeJSON(w, r, &content); err != nil {
 		return err
 	}
+	if delayed {
+		return c.scheduleDelayed(w, r, delayedevents.ScheduleRequest{
+			UserID: auth.UserID, DeviceID: auth.DeviceID, RoomID: roomID,
+			Type: eventType, Content: content, Delay: delay,
+		})
+	}
 
 	eventID, err := c.rooms.SendEvent(r.Context(), roomserver.SendEventRequest{
 		RoomID:      roomID,
@@ -191,10 +202,20 @@ func (c *ClientAPI) handlePutState(w http.ResponseWriter, r *http.Request, auth
 	}
 	stateKey := r.PathValue("stateKey")
 
+	delay, delayed, err := c.delayRequested(r)
+	if err != nil {
+		return err
+	}
 	var content sendEventRequest
 	if err := httputil.DecodeJSON(w, r, &content); err != nil {
 		return err
 	}
+	if delayed {
+		return c.scheduleDelayed(w, r, delayedevents.ScheduleRequest{
+			UserID: auth.UserID, DeviceID: auth.DeviceID, RoomID: roomID,
+			Type: eventType, StateKey: &stateKey, Content: content, Delay: delay,
+		})
+	}
 
 	eventID, err := c.rooms.SendEvent(r.Context(), roomserver.SendEventRequest{
 		RoomID:   roomID,
diff --git a/server/internal/clientapi/rtc.go b/server/internal/clientapi/rtc.go
new file mode 100644
index 0000000..d428b20
--- /dev/null
+++ b/server/internal/clientapi/rtc.go
@@ -0,0 +1,51 @@
+package clientapi
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/dariuszjaniak/warp/server/internal/httputil"
+	"github.com/dariuszjaniak/warp/server/internal/userapi"
+)
+
+// rtcTransportsPath is MSC4143's endpoint for the group call backends a
+// client may use: the same list /.well-known/matrix/client carries as
+// org.matrix.msc4143.rtc_foci, behind authentication and without needing
+// the discovery document.
+const rtcTransportsPath = "/_matrix/client/unstable/org.matrix.msc4143/rtc/transports"
+
+// RTCTransport is one group call backend: a LiveKit SFU, named by the JWT
+// service that hands out tokens for it.
+type RTCTransport struct {
+	Type              string `json:"type"`
+	LiveKitServiceURL string `json:"livekit_service_url"`
+}
+
+// RTCTransports lists the configured group call backends, or nil for none.
+func RTCTransports(liveKitServiceURL string) []RTCTransport {
+	if liveKitServiceURL == "" {
+		return nil
+	}
+	return []RTCTransport{{Type: "livekit", LiveKitServiceURL: strings.TrimRight(liveKitServiceURL, "/")}}
+}
+
+type rtcTransportsResponse struct {
+	Transports []RTCTransport `json:"rtc_transports"`
+}
+
+// registerRTCRoutes adds the MSC4143 endpoint, if a backend is configured.
+// Without one it is left unregistered: the 404 is how a client learns there
+// is none.
+func (c *ClientAPI) registerRTCRoutes(r *httputil.Router) {
+	if len(c.rtcTransports) == 0 {
+		return
+	}
+	c.authed(r, "GET "+rtcTransportsPath, c.limitDefault, c.handleRTCTransports)
+}
+
+// handleRTCTransports implements
+// GET /_matrix/client/unstable/org.matrix.msc4143/rtc/transports.
+func (c *ClientAPI) handleRTCTransports(w http.ResponseWriter, _ *http.Request, _ userapi.Authenticated) error {
+	httputil.WriteJSON(w, http.StatusOK, rtcTransportsResponse{Transports: c.rtcTransports})
+	return nil
+}
diff --git a/server/internal/clientapi/voip_test.go b/server/internal/clientapi/voip_test.go
index 5ad3e2c..387fd5c 100644
--- a/server/internal/clientapi/voip_test.go
+++ b/server/internal/clientapi/voip_test.go
@@ -87,3 +87,27 @@ func TestTurnServerStatic(t *testing.T) {
 		t.Errorf("response = %+v", got)
 	}
 }
+
+func TestRTCTransports(t *testing.T) {
+	const path = "/_matrix/client/unstable/org.matrix.msc4143/rtc/transports"
+	ts := newTestServer(t, func(o *clientapi.Options) {
+		o.RTC = config.RTC{LiveKitServiceURL: "https://livekit-jwt.warp.example/"}
+	})
+	acc := ts.register("alice", "correct horse battery")
+	expectError(t, ts.get(path, ""), http.StatusUnauthorized, "M_MISSING_TOKEN")
+
+	rec := ts.get(path, acc.AccessToken)
+	expectStatus(t, rec, http.StatusOK)
+	got := decode[struct {
+		Transports []map[string]string `json:"rtc_transports"`
+	}](t, rec)
+	if len(got.Transports) != 1 || got.Transports[0]["type"] != "livekit" ||
+		got.Transports[0]["livekit_service_url"] != "https://livekit-jwt.warp.example" {
+		t.Errorf("rtc_transports = %v", got.Transports)
+	}
+
+	// Without a backend there is no endpoint, which is how a client knows.
+	ts = newTestServer(t, nil)
+	acc = ts.register("alice", "correct horse battery")
+	expectError(t, ts.get(path, acc.AccessToken), http.StatusNotFound, "M_UNRECOGNIZED")
+}
diff --git a/server/internal/config/config.go b/server/internal/config/config.go
index 75a7ce2..61f81d9 100644
--- a/server/internal/config/config.go
+++ b/server/internal/config/config.go
@@ -182,6 +182,39 @@ type ClientAPI struct {
 	// TURN is what GET /voip/turnServer hands clients for voice and video
 	// calls.
 	TURN TURN `yaml:"turn"`
+
+	// RTC is the media backend for group calls (MatrixRTC), advertised in
+	// /.well-known/matrix/client.
+	RTC RTC `yaml:"rtc"`
+
+	// DelayedEvents bounds the delayed events (MSC4140) a client may
+	// schedule. Group calls depend on them: a member's "I left" is
+	// scheduled in advance, so a client that disappears still leaves.
+	DelayedEvents DelayedEvents `yaml:"delayed_events"`
+}
+
+// RTC configures group calls. Warp does not carry call media itself:
+// MatrixRTC clients publish to a LiveKit SFU, and get the token for it from
+// a LiveKit JWT service (lk-jwt-service) in exchange for an OpenID token
+// from this server. With no service URL no focus is advertised, and clients
+// that need one cannot start a group call.
+type RTC struct {
+	// LiveKitServiceURL is the base URL of the LiveKit JWT service, e.g.
+	// "https://livekit-jwt.example.org". It is advertised as an
+	// org.matrix.msc4143.rtc_foci entry of type livekit.
+	LiveKitServiceURL string `yaml:"livekit_service_url" env:"WARP_RTC_LIVEKIT_SERVICE_URL"`
+}
+
+// DelayedEvents configures MSC4140 delayed events.
+type DelayedEvents struct {
+	// MaxDelay is the longest delay a client may ask for. Zero turns
+	// delayed events off: the delay parameter is refused and the feature
+	// is not advertised.
+	MaxDelay time.Duration `yaml:"max_delay" env:"WARP_DELAYED_EVENTS_MAX_DELAY"`
+
+	// MaxPerUser caps how many delayed events one user may have scheduled
+	// at once.
+	MaxPerUser int `yaml:"max_per_user" env:"WARP_DELAYED_EVENTS_MAX_PER_USER"`
 }
 
 // TURN configures the relay servers clients use to set up calls. With no
@@ -531,6 +564,10 @@ func Default() *Config {
 				Media: RateLimitBucket{Burst: 100, Interval: 20 * time.Millisecond},
 			},
 			TURN: TURN{UserLifetime: time.Hour},
+			// A MatrixRTC client restarts its delayed leave every few
+			// seconds; a day leaves room for other uses without letting a
+			// forgotten event linger for weeks.
+			DelayedEvents: DelayedEvents{MaxDelay: 24 * time.Hour, MaxPerUser: 100},
 		},
 		Sync: Sync{
 			Presence:        false,
@@ -714,6 +751,17 @@ func (c *Config) Validate() error {
 	if c.ClientAPI.TURN.SharedSecret != "" && c.ClientAPI.TURN.UserLifetime <= 0 {
 		bad("client_api.turn.user_lifetime: must be positive")
 	}
+	if raw := c.ClientAPI.RTC.LiveKitServiceURL; raw != "" {
+		if u, err := url.Parse(raw); err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" {
+			bad("client_api.rtc.livekit_service_url: must be an http(s) URL, got %q", raw)
+		}
+	}
+	if c.ClientAPI.DelayedEvents.MaxDelay < 0 {
+		bad("client_api.delayed_events.max_delay: must not be negative")
+	}
+	if c.ClientAPI.DelayedEvents.MaxDelay > 0 && c.ClientAPI.DelayedEvents.MaxPerUser < 1 {
+		bad("client_api.delayed_events.max_per_user: must be at least 1")
+	}
 	if c.Sync.TypingTimeout <= 0 {
 		bad("sync.typing_timeout: must be positive")
 	}
diff --git a/server/internal/delayedevents/delayedevents.go b/server/internal/delayedevents/delayedevents.go
new file mode 100644
index 0000000..5adf392
--- /dev/null
+++ b/server/internal/delayedevents/delayedevents.go
@@ -0,0 +1,463 @@
+// Package delayedevents implements MSC4140 delayed events: an event a client
+// hands the server now, to be sent later on the client's behalf unless the
+// client pushes it back or cancels it first.
+//
+// It is what makes MatrixRTC group calls robust. A member joining a call
+// sends its call.member state, and schedules an empty one to replace it a
+// few seconds out; while it is in the call it keeps restarting that delay.
+// A client that crashes, loses its network or is closed stops restarting
+// it, and the server sends the "left" for it.
+//
+// Events are kept in the database, so a restart of the server does not
+// lose them, and are sent by a single scheduler goroutine that sleeps until
+// the next one is due.
+package delayedevents
+
+import (
+	"context"
+	"crypto/rand"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"log/slog"
+	"sync"
+	"time"
+
+	"github.com/dariuszjaniak/warp/server/internal/roomserver"
+	"github.com/dariuszjaniak/warp/server/internal/storage"
+)
+
+// Outcomes and reasons a finalised event is reported with, as MSC4140
+// names them.
+const (
+	OutcomeSend   = "send"
+	OutcomeCancel = "cancel"
+
+	ReasonDelay  = "delay"
+	ReasonAction = "action"
+	ReasonError  = "error"
+)
+
+var (
+	// ErrDisabled is returned when delayed events are switched off.
+	ErrDisabled = errors.New("delayed events are disabled")
+
+	// ErrMaxDelayExceeded is returned for a delay longer than the
+	// configured maximum.
+	ErrMaxDelayExceeded = errors.New("the requested delay exceeds the allowed maximum")
+
+	// ErrTooMany is returned when the user already has as many delayed
+	// events scheduled as they may.
+	ErrTooMany = errors.New("too many delayed events are scheduled")
+
+	// ErrNoSuchDelayedEvent is returned for a delay ID that is unknown or
+	// no longer scheduled.
+	ErrNoSuchDelayedEvent = storage.ErrNoSuchDelayedEvent
+)
+
+// finalisedRetention is how long a sent or cancelled event is kept for a
+// client to look up.
+const finalisedRetention = 24 * time.Hour
+
+// idleCheck is how long the scheduler sleeps with nothing scheduled. It
+// also paces the purge of finalised events.
+const idleCheck = time.Hour
+
+// dueBatch is how many due events are read at once.
+const dueBatch = 100
+
+// Sender sends an event into a room as a user: the roomserver.
+type Sender interface {
+	SendEvent(ctx context.Context, req roomserver.SendEventRequest) (string, error)
+}
+
+// Options configure the service.
+type Options struct {
+	Store storage.DelayedEventStore
+	Rooms Sender
+
+	// MaxDelay is the longest delay allowed. Zero disables the service.
+	MaxDelay time.Duration
+
+	// MaxPerUser caps the events one user may have scheduled.
+	MaxPerUser int
+
+	// DescribeError turns the error a send failed with into the Matrix
+	// error a client is shown. Nil reports every failure as M_UNKNOWN.
+	DescribeError func(error) json.RawMessage
+
+	Logger *slog.Logger
+	Now    func() time.Time
+}
+
+// Service schedules and sends delayed events.
+type Service struct {
+	store         storage.DelayedEventStore
+	rooms         Sender
+	maxDelay      time.Duration
+	maxPerUser    int
+	describeError func(error) json.RawMessage
+	log           *slog.Logger
+	now           func() time.Time
+
+	// mu serialises everything that finalises or moves an event, so the
+	// scheduler sending an event and its owner restarting or cancelling
+	// it cannot both win.
+	mu sync.Mutex
+
+	wake    chan struct{}
+	stop    chan struct{}
+	done    chan struct{}
+	started bool
+	closing sync.Once
+
+	// cancels tracks the background cancellations the emit stage starts,
+	// so Close can wait for them.
+	cancels sync.WaitGroup
+}
+
+// New builds the service. It does not start the scheduler.
+func New(opts Options) (*Service, error) {
+	if opts.Store == nil {
+		return nil, errors.New("delayedevents: Store must not be nil")
+	}
+	if opts.Rooms == nil {
+		return nil, errors.New("delayedevents: Rooms must not be nil")
+	}
+	if opts.Logger == nil {
+		opts.Logger = slog.Default()
+	}
+	if opts.Now == nil {
+		opts.Now = time.Now
+	}
+	if opts.DescribeError == nil {
+		opts.DescribeError = func(err error) json.RawMessage {
+			raw, _ := json.Marshal(map[string]string{"errcode": "M_UNKNOWN", "error": err.Error()})
+			return raw
+		}
+	}
+	return &Service{
+		store:         opts.Store,
+		rooms:         opts.Rooms,
+		maxDelay:      opts.MaxDelay,
+		maxPerUser:    opts.MaxPerUser,
+		describeError: opts.DescribeError,
+		log:           opts.Logger.With("component", "delayedevents"),
+		now:           opts.Now,
+		wake:          make(chan struct{}, 1),
+		stop:          make(chan struct{}),
+		done:          make(chan struct{}),
+	}, nil
+}
+
+// Enabled reports whether clients may schedule delayed events.
+func (s *Service) Enabled() bool { return s != nil && s.maxDelay > 0 }
+
+// MaxDelay is the longest delay a client may ask for.
+func (s *Service) MaxDelay() time.Duration { return s.maxDelay }
+
+// ScheduleRequest is an event to send later.
+type ScheduleRequest struct {
+	UserID   string
+	DeviceID string
+	RoomID   string
+	Type     string
+
+	// StateKey makes this a state event when it is non-nil.
+	StateKey *string
+	Content  json.RawMessage
+	Delay    time.Duration
+}
+
+// Schedule stores an event to be sent after req.Delay and returns its
+// delay ID.
+func (s *Service) Schedule(ctx context.Context, req ScheduleRequest) (string, error) {
+	if !s.Enabled() {
+		return "", ErrDisabled
+	}
+	if req.Delay < 0 {
+		return "", fmt.Errorf("%w: the delay must not be negative", roomserver.ErrInvalidContent)
+	}
+	if req.Delay > s.maxDelay {
+		return "", ErrMaxDelayExceeded
+	}
+	n, err := s.store.CountScheduledDelayedEvents(ctx, req.UserID)
+	if err != nil {
+		return "", err
+	}
+	if n >= s.maxPerUser {
+		return "", ErrTooMany
+	}
+	delayID, err := newDelayID()
+	if err != nil {
+		return "", err
+	}
+	nowMS := s.now().UnixMilli()
+	delayMS := req.Delay.Milliseconds()
+	if err := s.store.InsertDelayedEvent(ctx, storage.DelayedEvent{
+		DelayID:        delayID,
+		UserID:         req.UserID,
+		DeviceID:       req.DeviceID,
+		RoomID:         req.RoomID,
+		Type:           req.Type,
+		StateKey:       req.StateKey,
+		Content:        req.Content,
+		DelayMS:        delayMS,
+		RunningSinceMS: nowMS,
+		SendAtMS:       nowMS + delayMS,
+	}); err != nil {
+		return "", err
+	}
+	s.poke()
+	return delayID, nil
+}
+
+// Get returns one of a user's delayed events, scheduled or finalised.
+func (s *Service) Get(ctx context.Context, userID, delayID string) (storage.DelayedEvent, error) {
+	return s.store.DelayedEvent(ctx, userID, delayID)
+}
+
+// List returns a user's delayed events.
+func (s *Service) List(ctx context.Context, userID string) ([]storage.DelayedEvent, error) {
+	return s.store.DelayedEvents(ctx, userID)
+}
+
+// Restart starts a scheduled event's delay again from now.
+//
+// The action endpoints may be called without an access token: the delay
+// ID is the capability. That is what lets a MatrixRTC client hand its
+// delayed leave to a service that keeps it alive on its behalf.
+func (s *Service) Restart(ctx context.Context, delayID string) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if err := s.store.RestartDelayedEvent(ctx, delayID, s.now().UnixMilli()); err != nil {
+		return err
+	}
+	s.poke()
+	return nil
+}
+
+// Cancel drops a scheduled event without sending it.
+func (s *Service) Cancel(ctx context.Context, delayID string) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	e, err := s.store.ScheduledDelayedEvent(ctx, delayID)
+	if err != nil {
+		return err
+	}
+	return s.finalise(ctx, e, OutcomeCancel, ReasonAction, "", nil)
+}
+
+// Send sends a scheduled event now, without waiting for its delay. The
+// error of a failed send is returned as well as recorded.
+func (s *Service) Send(ctx context.Context, delayID string) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	e, err := s.store.ScheduledDelayedEvent(ctx, delayID)
+	if err != nil {
+		return err
+	}
+	return s.sendLocked(ctx, e, ReasonAction)
+}
+
+// sendLocked sends e and records the outcome. s.mu must be held.
+func (s *Service) sendLocked(ctx context.Context, e storage.DelayedEvent, reason string) error {
+	eventID, sendErr := s.rooms.SendEvent(ctx, roomserver.SendEventRequest{
+		RoomID:   e.RoomID,
+		Sender:   e.UserID,
+		Type:     e.Type,
+		StateKey: e.StateKey,
+		Content:  e.Content,
+	})
+	if sendErr != nil {
+		if err := s.finalise(ctx, e, OutcomeSend, ReasonError, "", s.describeError(sendErr)); err != nil {
+			return err
+		}
+		return sendErr
+	}
+	return s.finalise(ctx, e, OutcomeSend, reason, eventID, nil)
+}
+
+func (s *Service) finalise(ctx context.Context, e storage.DelayedEvent, outcome, reason, eventID string, errBody json.RawMessage) error {
+	e.FinalisedAtMS = s.now().UnixMilli()
+	e.Outcome = outcome
+	e.Reason = reason
+	e.EventID = eventID
+	e.Error = errBody
+	return s.store.FinaliseDelayedEvent(ctx, e)
+}
+
+// EventPersisted implements roomserver.Notifier.
+//
+// When someone else sets a piece of state, the delayed state events that
+// would overwrite it are cancelled: a delayed event stands for "put this
+// back if I stop answering", and must not clobber a change another user
+// made in the meantime. The owner's own updates leave them alone, which is
+// what lets a call member refresh its membership while its delayed leave
+// keeps running.
+//
+// The emit stage must not block, so the lookup runs in the background.
+func (s *Service) EventPersisted(_ context.Context, n roomserver.Notification) {
+	if !s.Enabled() || n.Event == nil || !n.StateChanged {
+		return
+	}
+	key, isState := n.Event.StateKey()
+	if !isState {
+		return
+	}
+	roomID, eventType, sender := n.RoomID, n.Event.Type(), n.Event.Sender()
+	select {
+	case <-s.stop:
+		return
+	default:
+	}
+	s.cancels.Add(1)
+	go func() {
+		defer s.cancels.Done()
+		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+		defer cancel()
+		s.cancelOverwritten(ctx, roomID, eventType, key, sender)
+	}()
+}
+
+func (s *Service) cancelOverwritten(ctx context.Context, roomID, eventType, stateKey, sender string) {
+	pending, err := s.store.ScheduledDelayedStateEvents(ctx, roomID, eventType, stateKey)
+	if err != nil {
+		s.log.Warn("could not look up delayed state events", "room_id", roomID, "error", err)
+		return
+	}
+	for _, e := range pending {
+		if e.UserID == sender {
+			continue
+		}
+		s.mu.Lock()
+		err := s.finalise(ctx, e, OutcomeCancel, ReasonAction, "", nil)
+		s.mu.Unlock()
+		if err != nil && !errors.Is(err, storage.ErrNoSuchDelayedEvent) {
+			s.log.Warn("could not cancel an overwritten delayed event", "delay_id", e.DelayID, "error", err)
+		}
+	}
+}
+
+// Start runs the scheduler until ctx is cancelled or Close is called.
+func (s *Service) Start(ctx context.Context) {
+	if !s.Enabled() || s.started {
+		return
+	}
+	s.started = true
+	go s.run(ctx)
+}
+
+// Close stops the scheduler and waits for it.
+func (s *Service) Close() {
+	s.closing.Do(func() { close(s.stop) })
+	if s.started {
+		<-s.done
+	}
+	s.cancels.Wait()
+}
+
+// poke wakes the scheduler to look at the schedule again.
+func (s *Service) poke() {
+	select {
+	case s.wake <- struct{}{}:
+	default:
+	}
+}
+
+func (s *Service) run(ctx context.Context) {
+	defer close(s.done)
+	timer := time.NewTimer(0)
+	defer timer.Stop()
+	lastPurge := time.Time{}
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-s.stop:
+			return
+		case <-timer.C:
+		case <-s.wake:
+		}
+
+		s.SendDue(ctx)
+		if now := s.now(); now.Sub(lastPurge) >= idleCheck {
+			lastPurge = now
+			if err := s.store.PurgeFinalisedDelayedEvents(ctx, now.Add(-finalisedRetention).UnixMilli()); err != nil {
+				s.log.Warn("could not purge finalised delayed events", "error", err)
+			}
+		}
+
+		wait := idleCheck
+		next, ok, err := s.store.NextDelayedEventDue(ctx)
+		switch {
+		case err != nil:
+			if ctx.Err() != nil {
+				return
+			}
+			s.log.Warn("could not read the delayed event schedule", "error", err)
+			wait = time.Second
+		case ok:
+			wait = min(max(time.Duration(next-s.now().UnixMilli())*time.Millisecond, 0), idleCheck)
+		}
+		if !timer.Stop() {
+			select {
+			case <-timer.C:
+			default:
+			}
+		}
+		timer.Reset(wait)
+	}
+}
+
+// SendDue sends every event whose delay has run out. The scheduler calls
+// it whenever the next event comes due; tests call it after moving the
+// clock.
+func (s *Service) SendDue(ctx context.Context) {
+	for {
+		due, err := s.store.DueDelayedEvents(ctx, s.now().UnixMilli(), dueBatch)
+		if err != nil {
+			if ctx.Err() == nil {
+				s.log.Warn("could not read due delayed events", "error", err)
+			}
+			return
+		}
+		for _, e := range due {
+			s.sendIfStillDue(ctx, e.DelayID)
+		}
+		if len(due) < dueBatch {
+			return
+		}
+	}
+}
+
+// sendIfStillDue re-reads an event under the lock, because its owner may
+// have restarted or cancelled it since the batch was read.
+func (s *Service) sendIfStillDue(ctx context.Context, delayID string) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	e, err := s.store.ScheduledDelayedEvent(ctx, delayID)
+	if err != nil {
+		return
+	}
+	if e.SendAtMS > s.now().UnixMilli() {
+		return
+	}
+	if err := s.sendLocked(ctx, e, ReasonDelay); err != nil {
+		s.log.Info("a delayed event could not be sent",
+			"delay_id", e.DelayID, "room_id", e.RoomID, "type", e.Type, "error", err)
+	}
+}
+
+// newDelayID makes a delay ID. It is a capability — anyone holding it may
+// restart, cancel or send the event — so it is as long as an access token's
+// random part.
+func newDelayID() (string, error) {
+	raw := make([]byte, 24)
+	if _, err := rand.Read(raw); err != nil {
+		return "", fmt.Errorf("generate delay ID: %w", err)
+	}
+	return "warp_de_" + base64.RawURLEncoding.EncodeToString(raw), nil
+}
diff --git a/server/internal/httputil/errors.go b/server/internal/httputil/errors.go
index 9e49e09..3cf974d 100644
--- a/server/internal/httputil/errors.go
+++ b/server/internal/httputil/errors.go
@@ -81,6 +81,11 @@ type MatrixError struct {
 	RemoteStatus int    `json:"status,omitempty"`
 	RemoteBody   string `json:"body,omitempty"`
 
+	// DelayedErrCode and MaxDelayMS accompany a delayed event whose delay
+	// is longer than the server allows (MSC4140).
+	DelayedErrCode string `json:"org.matrix.msc4140.errcode,omitempty"`
+	MaxDelayMS     int64  `json:"org.matrix.msc4140.max_delay,omitempty"`
+
 	// status is the HTTP status to send; not part of the JSON body.
 	status int
 }
diff --git a/server/internal/roomserver/create.go b/server/internal/roomserver/create.go
index e85c65a..4a213c9 100644
--- a/server/internal/roomserver/create.go
+++ b/server/internal/roomserver/create.go
@@ -432,6 +432,10 @@ func (r *API) powerLevelsContent(req CreateRoomRequest, preset string, rules roo
 			"m.room.avatar":             auth.DefaultStateDefault,
 			TypeEncryption:              100,
 			"m.room.server_acl":         100,
+			// Joining a group call is a state event of the member's own
+			// (MatrixRTC, MSC3401), so anyone who may talk in the room
+			// may also join its call. Starting one is not a separate act.
+			TypeCallMember: 0,
 		},
 		"notifications": map[string]any{"room": auth.DefaultNotification},
 	}
@@ -538,3 +542,7 @@ func mergeJSON(base, override json.RawMessage) (json.RawMessage, error) {
 	}
 	return json.Marshal(merged)
 }
+
+// TypeCallMember is a member's state in a room's group call (MatrixRTC).
+// It is still under its MSC3401 name, which is what clients send.
+const TypeCallMember = "org.matrix.msc3401.call.member"
diff --git a/server/internal/setup/routes.go b/server/internal/setup/routes.go
index 829c9e3..25b5760 100644
--- a/server/internal/setup/routes.go
+++ b/server/internal/setup/routes.go
@@ -1,10 +1,12 @@
 package setup
 
 import (
+	"maps"
 	"net/http"
 	"time"
 
 	"github.com/dariuszjaniak/warp/server/internal/buildinfo"
+	"github.com/dariuszjaniak/warp/server/internal/clientapi"
 	"github.com/dariuszjaniak/warp/server/internal/httputil"
 	"github.com/dariuszjaniak/warp/server/internal/tracing"
 )
@@ -32,10 +34,19 @@ type versionsResponse struct {
 	UnstableFeatures map[string]bool `json:"unstable_features,omitempty"`
 }
 
+// unstableDelayedEvents is the MSC4140 feature flag. It is advertised only
+// while delayed events are switched on, because a MatrixRTC client checks
+// it before scheduling its delayed leave.
+const unstableDelayedEvents = "org.matrix.msc4140"
+
 // wellKnownClient is the /.well-known/matrix/client document.
 type wellKnownClient struct {
 	Homeserver     wellKnownBaseURL  `json:"m.homeserver"`
 	IdentityServer *wellKnownBaseURL `json:"m.identity_server,omitempty"`
+
+	// RTCFoci are the MatrixRTC backends (MSC4143) a client may use for a
+	// group call it starts.
+	RTCFoci []clientapi.RTCTransport `json:"org.matrix.msc4143.rtc_foci,omitempty"`
 }
 
 type wellKnownBaseURL struct {
@@ -84,10 +95,14 @@ func (s *Server) routes() *httputil.Router {
 
 // handleVersions implements GET /_matrix/client/versions.
 func (s *Server) handleVersions(w http.ResponseWriter, _ *http.Request) error {
+	features := maps.Clone(UnstableFeatures)
+	if s.delayed.Enabled() {
+		features[unstableDelayedEvents] = true
+	}
 	httputil.CacheFor(w, time.Hour)
 	httputil.WriteJSON(w, http.StatusOK, versionsResponse{
 		Versions:         SpecVersions,
-		UnstableFeatures: UnstableFeatures,
+		UnstableFeatures: features,
 	})
 	return nil
 }
@@ -101,6 +116,7 @@ func (s *Server) handleWellKnownClient(w http.ResponseWriter, _ *http.Request) e
 	if url := s.cfg.Global.WellKnown.IdentityServerBaseURL; url != "" {
 		doc.IdentityServer = &wellKnownBaseURL{BaseURL: url}
 	}
+	doc.RTCFoci = clientapi.RTCTransports(s.cfg.ClientAPI.RTC.LiveKitServiceURL)
 	httputil.CacheFor(w, time.Hour)
 	httputil.WriteJSON(w, http.StatusOK, doc)
 	return nil
diff --git a/server/internal/setup/rtc_test.go b/server/internal/setup/rtc_test.go
new file mode 100644
index 0000000..40748ba
--- /dev/null
+++ b/server/internal/setup/rtc_test.go
@@ -0,0 +1,87 @@
+package setup_test
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/dariuszjaniak/warp/server/internal/config"
+)
+
+// TestWellKnownClientAdvertisesLiveKit: group call clients find the SFU
+// they publish to in the discovery document (MSC4143).
+func TestWellKnownClientAdvertisesLiveKit(t *testing.T) {
+	srv := newTestServer(t, func(c *config.Config) {
+		c.ClientAPI.RTC.LiveKitServiceURL = "https://livekit-jwt.warp.example/"
+	})
+	rec := get(t, srv, http.MethodGet, "/.well-known/matrix/client")
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d", rec.Code)
+	}
+	body := decode[struct {
+		Foci []map[string]string `json:"org.matrix.msc4143.rtc_foci"`
+	}](t, rec)
+	if len(body.Foci) != 1 || body.Foci[0]["type"] != "livekit" ||
+		body.Foci[0]["livekit_service_url"] != "https://livekit-jwt.warp.example" {
+		t.Errorf("rtc_foci = %v", body.Foci)
+	}
+}
+
+func TestWellKnownClientOmitsRTCFociByDefault(t *testing.T) {
+	srv := newTestServer(t, nil)
+	body := decode[map[string]any](t, get(t, srv, http.MethodGet, "/.well-known/matrix/client"))
+	if _, present := body["org.matrix.msc4143.rtc_foci"]; present {
+		t.Error("rtc_foci must be omitted when no LiveKit service is configured")
+	}
+}
+
+func TestRTCConfigValidation(t *testing.T) {
+	cfg := config.Default()
+	cfg.Global.ServerName = "warp.example"
+	cfg.ClientAPI.RTC.LiveKitServiceURL = "livekit-jwt.warp.example"
+	if err := cfg.Validate(); err == nil {
+		t.Error("a LiveKit service URL without a scheme was accepted")
+	}
+	cfg.ClientAPI.RTC.LiveKitServiceURL = ""
+	cfg.ClientAPI.DelayedEvents.MaxPerUser = 0
+	if err := cfg.Validate(); err == nil {
+		t.Error("delayed events with no room for any were accepted")
+	}
+}
+
+// TestGroupCallRoutesAreWiredUp: with a signing key (and so rooms) the
+// server advertises delayed events, serves their endpoints, and hands out
+// OpenID tokens the userinfo endpoint accepts.
+func TestGroupCallRoutesAreWiredUp(t *testing.T) {
+	srv := newSigningServer(t, func(c *config.Config) {
+		c.Registration.Enabled = true
+		c.ClientAPI.RateLimit.Enabled = false
+	})
+	features := decode[map[string]any](t, get(t, srv, http.MethodGet, "/_matrix/client/versions"))["unstable_features"].(map[string]any)
+	if features["org.matrix.msc4140"] != true {
+		t.Errorf("unstable_features = %v", features)
+	}
+
+	token := registerThrough(t, srv, "alice")
+	if rec := getWithToken(t, srv, "/_matrix/client/unstable/org.matrix.msc4140/delayed_events", token); rec.Code != http.StatusOK {
+		t.Errorf("delayed_events: %d %s", rec.Code, rec.Body.String())
+	}
+	rec := post(t, srv, "/_matrix/client/v3/user/@alice:warp.example/openid/request_token", map[string]any{}, token)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("request_token: %d %s", rec.Code, rec.Body.String())
+	}
+	openID := decode[map[string]any](t, rec)["access_token"].(string)
+	rec = get(t, srv, http.MethodGet, "/_matrix/federation/v1/openid/userinfo?access_token="+openID)
+	if rec.Code != http.StatusOK {
+		t.Errorf("userinfo: %d %s", rec.Code, rec.Body.String())
+	}
+}
+
+func TestDelayedEventsCanBeSwitchedOff(t *testing.T) {
+	srv := newSigningServer(t, func(c *config.Config) {
+		c.ClientAPI.DelayedEvents.MaxDelay = 0
+	})
+	features := decode[map[string]any](t, get(t, srv, http.MethodGet, "/_matrix/client/versions"))["unstable_features"].(map[string]any)
+	if _, present := features["org.matrix.msc4140"]; present {
+		t.Errorf("unstable_features = %v", features)
+	}
+}
diff --git a/server/internal/setup/server.go b/server/internal/setup/server.go
index 4ebc929..f39c31b 100644
--- a/server/internal/setup/server.go
+++ b/server/internal/setup/server.go
@@ -19,6 +19,7 @@ import (
 	"github.com/dariuszjaniak/warp/server/internal/buildinfo"
 	"github.com/dariuszjaniak/warp/server/internal/clientapi"
 	"github.com/dariuszjaniak/warp/server/internal/config"
+	"github.com/dariuszjaniak/warp/server/internal/delayedevents"
 	"github.com/dariuszjaniak/warp/server/internal/federation"
 	"github.com/dariuszjaniak/warp/server/internal/federationapi"
 	"github.com/dariuszjaniak/warp/server/internal/httputil"
@@ -61,6 +62,7 @@ type Server struct {
 	clientAPI *clientapi.ClientAPI
 
 	appservices *appservice.API
+	delayed     *delayedevents.Service
 	notices     *servernotices.API
 	regTokens   *userapi.RegistrationTokens
 
@@ -407,6 +409,24 @@ func New(ctx context.Context, cfg *config.Config, opts Options) (*Server, error)
 		}
 		emit.add(s.appservices)
 
+		// Delayed events are sent by the roomserver as the user who
+		// scheduled them, and hear about state changes on the emit stage:
+		// someone else setting a piece of state cancels the delayed
+		// events that would overwrite it.
+		s.delayed, err = delayedevents.New(delayedevents.Options{
+			Store:         s.db.DelayedEvents(),
+			Rooms:         s.rooms,
+			MaxDelay:      cfg.ClientAPI.DelayedEvents.MaxDelay,
+			MaxPerUser:    cfg.ClientAPI.DelayedEvents.MaxPerUser,
+			DescribeError: clientapi.DescribeRoomError,
+			Logger:        log,
+		})
+		if err != nil {
+			_ = s.closeDB()
+			return nil, err
+		}
+		emit.add(s.delayed)
+
 		// Deactivating an account leaves its rooms, which only the
 		// roomserver can do.
 		s.users.SetAccountObserver(roomLeaver{rooms: s.rooms, log: log})
@@ -490,6 +510,9 @@ func New(ctx context.Context, cfg *config.Config, opts Options) (*Server, error)
 		AppServices:          s.appservices,
 		RateLimit:            cfg.ClientAPI.RateLimit,
 		TURN:                 cfg.ClientAPI.TURN,
+		RTC:                  cfg.ClientAPI.RTC,
+		DelayedEvents:        s.delayed,
+		OpenIDTokens:         s.db.OpenIDTokens(),
 		TrustXForwardedFor:   cfg.ClientAPI.TrustXForwardedFor,
 		Logger:               log,
 	})
@@ -522,6 +545,11 @@ func New(ctx context.Context, cfg *config.Config, opts Options) (*Server, error)
 	// talks to the services, and tests that drive the handler directly
 	// need it running.
 	s.appservices.Start(ctx)
+	// So do delayed events: a call member who drops off has to be removed
+	// whether or not anything is listening yet.
+	if s.delayed != nil {
+		s.delayed.Start(ctx)
+	}
 
 	s.handler = httputil.Chain(s.routes(),
 		httputil.Recoverer,
@@ -749,6 +777,10 @@ func (s *Server) Close() error {
 		// cursors.
 		s.appservices.Close()
 	}
+	if s.delayed != nil {
+		// And the delayed event scheduler, which sends events.
+		s.delayed.Close()
+	}
 	if s.stopTracing != nil {
 		// Spans still in the batch are sent rather than lost.
 		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
diff --git a/server/internal/storage/delayed.go b/server/internal/storage/delayed.go
new file mode 100644
index 0000000..26a2410
--- /dev/null
+++ b/server/internal/storage/delayed.go
@@ -0,0 +1,110 @@
+package storage
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+)
+
+// ErrNoSuchDelayedEvent is returned for a delay ID that is unknown, belongs
+// to someone else, or is no longer scheduled.
+var ErrNoSuchDelayedEvent = errors.New("no such delayed event")
+
+// DelayedEvent is an event a client asked to have sent later (MSC4140).
+//
+// While it is scheduled FinalisedAtMS is zero. Once it has been sent or
+// cancelled it is kept for a while with its outcome, so a client that comes
+// back can find out what became of it.
+type DelayedEvent struct {
+	DelayID  string
+	UserID   string
+	DeviceID string
+	RoomID   string
+	Type     string
+
+	// StateKey is nil for a timeline event.
+	StateKey *string
+	Content  json.RawMessage
+
+	// DelayMS is the delay the client asked for. A restart counts it again
+	// from now.
+	DelayMS int64
+
+	// RunningSinceMS is when the delay was last (re)started, and SendAtMS
+	// when it runs out: RunningSinceMS + DelayMS.
+	RunningSinceMS int64
+	SendAtMS       int64
+
+	// The outcome, once finalised: Outcome is "send" or "cancel", Reason
+	// "delay", "action" or "error". EventID is the event that was sent,
+	// and Error the Matrix error that stopped it.
+	FinalisedAtMS int64
+	Outcome       string
+	Reason        string
+	EventID       string
+	Error         json.RawMessage
+}
+
+// DelayedEventStore keeps the delayed events of every user.
+type DelayedEventStore interface {
+	// InsertDelayedEvent schedules an event.
+	InsertDelayedEvent(ctx context.Context, e DelayedEvent) error
+
+	// DelayedEvent returns one of userID's events, scheduled or finalised.
+	DelayedEvent(ctx context.Context, userID, delayID string) (DelayedEvent, error)
+
+	// ScheduledDelayedEvent returns a scheduled event whoever owns it: the
+	// action endpoints are addressed by the delay ID alone.
+	ScheduledDelayedEvent(ctx context.Context, delayID string) (DelayedEvent, error)
+
+	// DelayedEvents lists userID's events, scheduled ones first by when
+	// they are due, then finalised ones newest first.
+	DelayedEvents(ctx context.Context, userID string) ([]DelayedEvent, error)
+
+	// CountScheduledDelayedEvents counts userID's scheduled events.
+	CountScheduledDelayedEvents(ctx context.Context, userID string) (int, error)
+
+	// RestartDelayedEvent starts a scheduled event's delay again from nowMS.
+	// It returns ErrNoSuchDelayedEvent if the event is not scheduled.
+	RestartDelayedEvent(ctx context.Context, delayID string, nowMS int64) error
+
+	// FinaliseDelayedEvent records what became of a scheduled event. It
+	// returns ErrNoSuchDelayedEvent if the event was already finalised,
+	// which is how two racing finalisers are told apart: only one of them
+	// gets to send.
+	FinaliseDelayedEvent(ctx context.Context, e DelayedEvent) error
+
+	// DueDelayedEvents returns up to limit scheduled events whose delay
+	// has run out at nowMS, the earliest first.
+	DueDelayedEvents(ctx context.Context, nowMS int64, limit int) ([]DelayedEvent, error)
+
+	// NextDelayedEventDue reports when the next scheduled event is due,
+	// and false when nothing is scheduled.
+	NextDelayedEventDue(ctx context.Context) (int64, bool, error)
+
+	// ScheduledDelayedStateEvents lists the scheduled state events for one
+	// piece of room state, of every user.
+	ScheduledDelayedStateEvents(ctx context.Context, roomID, eventType, stateKey string) ([]DelayedEvent, error)
+
+	// PurgeFinalisedDelayedEvents forgets the events finalised before
+	// beforeMS.
+	PurgeFinalisedDelayedEvents(ctx context.Context, beforeMS int64) error
+}
+
+// ErrNoSuchOpenIDToken is returned for an OpenID token that is unknown or
+// has expired.
+var ErrNoSuchOpenIDToken = errors.New("no such OpenID token")
+
+// OpenIDTokenStore keeps the OpenID tokens users hand to third parties, so
+// those can find out who the user is (and nothing more) from this server.
+type OpenIDTokenStore interface {
+	// InsertOpenIDToken stores a token by its hash.
+	InsertOpenIDToken(ctx context.Context, tokenHash, userID string, expiresAtMS int64) error
+
+	// OpenIDTokenUser returns the user a token was issued to, or
+	// ErrNoSuchOpenIDToken once it has expired at nowMS.
+	OpenIDTokenUser(ctx context.Context, tokenHash string, nowMS int64) (string, error)
+
+	// PurgeOpenIDTokens forgets tokens that expired before beforeMS.
+	PurgeOpenIDTokens(ctx context.Context, beforeMS int64) error
+}
diff --git a/server/internal/storage/delayed_test.go b/server/internal/storage/delayed_test.go
new file mode 100644
index 0000000..e121228
--- /dev/null
+++ b/server/internal/storage/delayed_test.go
@@ -0,0 +1,147 @@
+package storage_test
+
+import (
+	"database/sql"
+	"errors"
+	"os"
+	"testing"
+
+	"github.com/dariuszjaniak/warp/server/internal/storage"
+)
+
+// migratedDelayedDB opens a migrated database with empty delayed event and
+// OpenID tables.
+func migratedDelayedDB(t *testing.T, driver string) storage.Database {
+	t.Helper()
+	db := openTestDB(t, driver)
+	if err := db.Migrate(t.Context()); err != nil {
+		t.Fatalf("Migrate: %v", err)
+	}
+	if driver == storage.DriverPostgres {
+		pool, err := sql.Open("pgx", os.Getenv("WARP_TEST_POSTGRES_DSN"))
+		if err != nil {
+			t.Fatalf("open postgres: %v", err)
+		}
+		defer func() { _ = pool.Close() }()
+		if _, err := pool.ExecContext(t.Context(), `TRUNCATE delayed_events, openid_tokens`); err != nil {
+			t.Fatalf("reset the tables: %v", err)
+		}
+	}
+	return db
+}
+
+func TestDelayedEvents(t *testing.T) {
+	for _, driver := range testDrivers {
+		t.Run(driver, func(t *testing.T) {
+			ctx := t.Context()
+			store := migratedDelayedDB(t, driver).DelayedEvents()
+
+			if _, ok, err := store.NextDelayedEventDue(ctx); err != nil || ok {
+				t.Fatalf("NextDelayedEventDue on an empty table = %v, %v", ok, err)
+			}
+
+			key := "_@alice:warp.example_DEV_m.call"
+			state := storage.DelayedEvent{
+				DelayID: "d1", UserID: "@alice:warp.example", DeviceID: "DEV",
+				RoomID: "!r:warp.example", Type: "org.matrix.msc3401.call.member",
+				StateKey: &key, Content: []byte(`{}`),
+				DelayMS: 5000, RunningSinceMS: 1000, SendAtMS: 6000,
+			}
+			timeline := storage.DelayedEvent{
+				DelayID: "d2", UserID: "@alice:warp.example", RoomID: "!r:warp.example",
+				Type: "m.room.message", Content: []byte(`{"body":"hi"}`),
+				DelayMS: 1000, RunningSinceMS: 1000, SendAtMS: 2000,
+			}
+			for _, e := range []storage.DelayedEvent{state, timeline} {
+				if err := store.InsertDelayedEvent(ctx, e); err != nil {
+					t.Fatalf("InsertDelayedEvent: %v", err)
+				}
+			}
+
+			if n, err := store.CountScheduledDelayedEvents(ctx, "@alice:warp.example"); err != nil || n != 2 {
+				t.Errorf("count = %d, %v", n, err)
+			}
+			if next, ok, err := store.NextDelayedEventDue(ctx); err != nil || !ok || next != 2000 {
+				t.Errorf("next due = %d, %v, %v", next, ok, err)
+			}
+
+			got, err := store.DelayedEvent(ctx, "@alice:warp.example", "d1")
+			if err != nil || got.StateKey == nil || *got.StateKey != key || string(got.Content) != `{}` {
+				t.Errorf("DelayedEvent = %+v, %v", got, err)
+			}
+			if got, err := store.DelayedEvent(ctx, "@alice:warp.example", "d2"); err != nil || got.StateKey != nil {
+				t.Errorf("a timeline event has a state key: %+v, %v", got, err)
+			}
+			if _, err := store.DelayedEvent(ctx, "@bob:warp.example", "d1"); !errors.Is(err, storage.ErrNoSuchDelayedEvent) {
+				t.Errorf("bob read alice's event: %v", err)
+			}
+
+			due, err := store.DueDelayedEvents(ctx, 3000, 10)
+			if err != nil || len(due) != 1 || due[0].DelayID != "d2" {
+				t.Errorf("due at 3000 = %+v, %v", due, err)
+			}
+
+			if err := store.RestartDelayedEvent(ctx, "d1", 4000); err != nil {
+				t.Fatalf("RestartDelayedEvent: %v", err)
+			}
+			got, _ = store.ScheduledDelayedEvent(ctx, "d1")
+			if got.RunningSinceMS != 4000 || got.SendAtMS != 9000 {
+				t.Errorf("after restart = %+v", got)
+			}
+
+			pending, err := store.ScheduledDelayedStateEvents(ctx, "!r:warp.example", "org.matrix.msc3401.call.member", key)
+			if err != nil || len(pending) != 1 {
+				t.Errorf("ScheduledDelayedStateEvents = %+v, %v", pending, err)
+			}
+
+			sent := timeline
+			sent.FinalisedAtMS, sent.Outcome, sent.Reason, sent.EventID = 2500, "send", "delay", "$e"
+			if err := store.FinaliseDelayedEvent(ctx, sent); err != nil {
+				t.Fatalf("FinaliseDelayedEvent: %v", err)
+			}
+			if err := store.FinaliseDelayedEvent(ctx, sent); !errors.Is(err, storage.ErrNoSuchDelayedEvent) {
+				t.Errorf("finalising twice = %v", err)
+			}
+			if err := store.RestartDelayedEvent(ctx, "d2", 3000); !errors.Is(err, storage.ErrNoSuchDelayedEvent) {
+				t.Errorf("restarting a finalised event = %v", err)
+			}
+
+			all, err := store.DelayedEvents(ctx, "@alice:warp.example")
+			if err != nil || len(all) != 2 || all[0].DelayID != "d1" || all[1].EventID != "$e" {
+				t.Errorf("DelayedEvents = %+v, %v", all, err)
+			}
+
+			if err := store.PurgeFinalisedDelayedEvents(ctx, 3000); err != nil {
+				t.Fatal(err)
+			}
+			if all, _ := store.DelayedEvents(ctx, "@alice:warp.example"); len(all) != 1 {
+				t.Errorf("after purge = %+v", all)
+			}
+		})
+	}
+}
+
+func TestOpenIDTokens(t *testing.T) {
+	for _, driver := range testDrivers {
+		t.Run(driver, func(t *testing.T) {
+			ctx := t.Context()
+			store := migratedDelayedDB(t, driver).OpenIDTokens()
+
+			if err := store.InsertOpenIDToken(ctx, "hash", "@alice:warp.example", 5000); err != nil {
+				t.Fatal(err)
+			}
+			if user, err := store.OpenIDTokenUser(ctx, "hash", 4000); err != nil || user != "@alice:warp.example" {
+				t.Errorf("OpenIDTokenUser = %q, %v", user, err)
+			}
+			if _, err := store.OpenIDTokenUser(ctx, "hash", 6000); !errors.Is(err, storage.ErrNoSuchOpenIDToken) {
+				t.Errorf("an expired token = %v", err)
+			}
+			if err := store.PurgeOpenIDTokens(ctx, 6000); err != nil {
+				t.Fatal(err)
+			}
+			if _, err := store.OpenIDTokenUser(ctx, "hash", 0); !errors.Is(err, storage.ErrNoSuchOpenIDToken) {
+				t.Errorf("a purged token = %v", err)
+			}
+		})
+	}
+}
diff --git a/server/internal/storage/postgres/migrations/0014_delayed_events_openid.sql b/server/internal/storage/postgres/migrations/0014_delayed_events_openid.sql
new file mode 100644
index 0000000..b009528
--- /dev/null
+++ b/server/internal/storage/postgres/migrations/0014_delayed_events_openid.sql
@@ -0,0 +1,50 @@
+-- Group calls: delayed events (MSC4140) and OpenID tokens.
+
+-- An event a client asked to have sent later. A MatrixRTC client schedules
+-- its own "left the call" this way and keeps pushing it back while it is
+-- in the call, so a client that crashes or loses its connection still
+-- leaves.
+--
+-- state_key is NULL for a timeline event. finalised_at_ms is 0 while the
+-- event is scheduled; once it has been sent or cancelled the row is kept
+-- for a while with its outcome, so a client can find out what happened.
+CREATE TABLE IF NOT EXISTS delayed_events (
+    delay_id          TEXT   NOT NULL PRIMARY KEY,
+    user_id           TEXT   NOT NULL,
+    device_id         TEXT   NOT NULL DEFAULT '',
+    room_id           TEXT   NOT NULL,
+    event_type        TEXT   NOT NULL,
+    state_key         TEXT,
+    content           TEXT   NOT NULL,
+    delay_ms          BIGINT NOT NULL,
+    running_since_ms  BIGINT NOT NULL,
+    send_at_ms        BIGINT NOT NULL,
+    finalised_at_ms   BIGINT NOT NULL DEFAULT 0,
+    outcome           TEXT   NOT NULL DEFAULT '',
+    reason            TEXT   NOT NULL DEFAULT '',
+    event_id          TEXT   NOT NULL DEFAULT '',
+    error             TEXT   NOT NULL DEFAULT ''
+);
+
+CREATE INDEX IF NOT EXISTS delayed_events_user_idx
+    ON delayed_events (user_id, finalised_at_ms);
+
+-- The scheduler asks for what is due next among the scheduled events.
+CREATE INDEX IF NOT EXISTS delayed_events_due_idx
+    ON delayed_events (finalised_at_ms, send_at_ms);
+
+-- Someone else setting a piece of state cancels the delayed events that
+-- would have overwritten it.
+CREATE INDEX IF NOT EXISTS delayed_events_state_idx
+    ON delayed_events (room_id, event_type, state_key, finalised_at_ms);
+
+-- OpenID tokens: what a user hands a third party (the LiveKit JWT service)
+-- so it can ask this server who they are. Stored by hash, like access
+-- tokens.
+CREATE TABLE IF NOT EXISTS openid_tokens (
+    token_hash    TEXT   NOT NULL PRIMARY KEY,
+    user_id       TEXT   NOT NULL,
+    expires_at_ms BIGINT NOT NULL
+);
+
+CREATE INDEX IF NOT EXISTS openid_tokens_expiry_idx ON openid_tokens (expires_at_ms);
diff --git a/server/internal/storage/sqlite/migrations/0014_delayed_events_openid.sql b/server/internal/storage/sqlite/migrations/0014_delayed_events_openid.sql
new file mode 100644
index 0000000..b009528
--- /dev/null
+++ b/server/internal/storage/sqlite/migrations/0014_delayed_events_openid.sql
@@ -0,0 +1,50 @@
+-- Group calls: delayed events (MSC4140) and OpenID tokens.
+
+-- An event a client asked to have sent later. A MatrixRTC client schedules
+-- its own "left the call" this way and keeps pushing it back while it is
+-- in the call, so a client that crashes or loses its connection still
+-- leaves.
+--
+-- state_key is NULL for a timeline event. finalised_at_ms is 0 while the
+-- event is scheduled; once it has been sent or cancelled the row is kept
+-- for a while with its outcome, so a client can find out what happened.
+CREATE TABLE IF NOT EXISTS delayed_events (
+    delay_id          TEXT   NOT NULL PRIMARY KEY,
+    user_id           TEXT   NOT NULL,
+    device_id         TEXT   NOT NULL DEFAULT '',
+    room_id           TEXT   NOT NULL,
+    event_type        TEXT   NOT NULL,
+    state_key         TEXT,
+    content           TEXT   NOT NULL,
+    delay_ms          BIGINT NOT NULL,
+    running_since_ms  BIGINT NOT NULL,
+    send_at_ms        BIGINT NOT NULL,
+    finalised_at_ms   BIGINT NOT NULL DEFAULT 0,
+    outcome           TEXT   NOT NULL DEFAULT '',
+    reason            TEXT   NOT NULL DEFAULT '',
+    event_id          TEXT   NOT NULL DEFAULT '',
+    error             TEXT   NOT NULL DEFAULT ''
+);
+
+CREATE INDEX IF NOT EXISTS delayed_events_user_idx
+    ON delayed_events (user_id, finalised_at_ms);
+
+-- The scheduler asks for what is due next among the scheduled events.
+CREATE INDEX IF NOT EXISTS delayed_events_due_idx
+    ON delayed_events (finalised_at_ms, send_at_ms);
+
+-- Someone else setting a piece of state cancels the delayed events that
+-- would have overwritten it.
+CREATE INDEX IF NOT EXISTS delayed_events_state_idx
+    ON delayed_events (room_id, event_type, state_key, finalised_at_ms);
+
+-- OpenID tokens: what a user hands a third party (the LiveKit JWT service)
+-- so it can ask this server who they are. Stored by hash, like access
+-- tokens.
+CREATE TABLE IF NOT EXISTS openid_tokens (
+    token_hash    TEXT   NOT NULL PRIMARY KEY,
+    user_id       TEXT   NOT NULL,
+    expires_at_ms BIGINT NOT NULL
+);
+
+CREATE INDEX IF NOT EXISTS openid_tokens_expiry_idx ON openid_tokens (expires_at_ms);
diff --git a/server/internal/storage/sqlstore/delayed.go b/server/internal/storage/sqlstore/delayed.go
new file mode 100644
index 0000000..5432c92
--- /dev/null
+++ b/server/internal/storage/sqlstore/delayed.go
@@ -0,0 +1,273 @@
+package sqlstore
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+
+	"github.com/dariuszjaniak/warp/server/internal/storage"
+)
+
+// DelayedEvents is the shared implementation of storage.DelayedEventStore.
+type DelayedEvents struct {
+	db     *sql.DB
+	rebind func(string) string
+}
+
+// NewDelayedEvents builds a delayed event store.
+func NewDelayedEvents(db *sql.DB, rebind func(string) string) *DelayedEvents {
+	if rebind == nil {
+		rebind = func(query string) string { return query }
+	}
+	return &DelayedEvents{db: db, rebind: rebind}
+}
+
+func (s *DelayedEvents) q(query string) string { return s.rebind(query) }
+
+const delayedEventColumns = `
+	delay_id, user_id, device_id, room_id, event_type, state_key, content,
+	delay_ms, running_since_ms, send_at_ms,
+	finalised_at_ms, outcome, reason, event_id, error`
+
+const (
+	insertDelayedEventSQL = `
+		INSERT INTO delayed_events (
+			delay_id, user_id, device_id, room_id, event_type, state_key, content,
+			delay_ms, running_since_ms, send_at_ms)
+		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`
+
+	selectDelayedEventSQL = `SELECT` + delayedEventColumns + `
+		FROM delayed_events WHERE user_id = ? AND delay_id = ?`
+
+	selectScheduledDelayedEventSQL = `SELECT` + delayedEventColumns + `
+		FROM delayed_events WHERE delay_id = ? AND finalised_at_ms = 0`
+
+	selectUserDelayedEventsSQL = `SELECT` + delayedEventColumns + `
+		FROM delayed_events WHERE user_id = ?
+		ORDER BY finalised_at_ms = 0 DESC, send_at_ms ASC, finalised_at_ms DESC`
+
+	countScheduledDelayedEventsSQL = `
+		SELECT COUNT(*) FROM delayed_events WHERE user_id = ? AND finalised_at_ms = 0`
+
+	restartDelayedEventSQL = `
+		UPDATE delayed_events SET running_since_ms = ?, send_at_ms = ? + delay_ms
+		WHERE delay_id = ? AND finalised_at_ms = 0`
+
+	finaliseDelayedEventSQL = `
+		UPDATE delayed_events
+		SET finalised_at_ms = ?, outcome = ?, reason = ?, event_id = ?, error = ?
+		WHERE delay_id = ? AND finalised_at_ms = 0`
+
+	selectDueDelayedEventsSQL = `SELECT` + delayedEventColumns + `
+		FROM delayed_events WHERE finalised_at_ms = 0 AND send_at_ms <= ?
+		ORDER BY send_at_ms LIMIT ?`
+
+	selectNextDelayedEventDueSQL = `
+		SELECT MIN(send_at_ms) FROM delayed_events WHERE finalised_at_ms = 0`
+
+	selectScheduledStateEventsSQL = `SELECT` + delayedEventColumns + `
+		FROM delayed_events
+		WHERE room_id = ? AND event_type = ? AND state_key = ? AND finalised_at_ms = 0`
+
+	purgeFinalisedDelayedEventsSQL = `
+		DELETE FROM delayed_events WHERE finalised_at_ms <> 0 AND finalised_at_ms < ?`
+)
+
+// InsertDelayedEvent implements storage.DelayedEventStore.
+func (s *DelayedEvents) InsertDelayedEvent(ctx context.Context, e storage.DelayedEvent) error {
+	var stateKey sql.NullString
+	if e.StateKey != nil {
+		stateKey = sql.NullString{String: *e.StateKey, Valid: true}
+	}
+	if _, err := s.db.ExecContext(ctx, s.q(insertDelayedEventSQL),
+		e.DelayID, e.UserID, e.DeviceID, e.RoomID, e.Type, stateKey, string(e.Content),
+		e.DelayMS, e.RunningSinceMS, e.SendAtMS,
+	); err != nil {
+		return fmt.Errorf("insert delayed event: %w", err)
+	}
+	return nil
+}
+
+// DelayedEvent implements storage.DelayedEventStore.
+func (s *DelayedEvents) DelayedEvent(ctx context.Context, userID, delayID string) (storage.DelayedEvent, error) {
+	return s.one(ctx, selectDelayedEventSQL, userID, delayID)
+}
+
+// ScheduledDelayedEvent implements storage.DelayedEventStore.
+func (s *DelayedEvents) ScheduledDelayedEvent(ctx context.Context, delayID string) (storage.DelayedEvent, error) {
+	return s.one(ctx, selectScheduledDelayedEventSQL, delayID)
+}
+
+func (s *DelayedEvents) one(ctx context.Context, query string, args ...any) (storage.DelayedEvent, error) {
+	events, err := s.list(ctx, query, args...)
+	if err != nil {
+		return storage.DelayedEvent{}, err
+	}
+	if len(events) == 0 {
+		return storage.DelayedEvent{}, storage.ErrNoSuchDelayedEvent
+	}
+	return events[0], nil
+}
+
+// DelayedEvents implements storage.DelayedEventStore.
+func (s *DelayedEvents) DelayedEvents(ctx context.Context, userID string) ([]storage.DelayedEvent, error) {
+	return s.list(ctx, selectUserDelayedEventsSQL, userID)
+}
+
+// CountScheduledDelayedEvents implements storage.DelayedEventStore.
+func (s *DelayedEvents) CountScheduledDelayedEvents(ctx context.Context, userID string) (int, error) {
+	var n int
+	if err := s.db.QueryRowContext(ctx, s.q(countScheduledDelayedEventsSQL), userID).Scan(&n); err != nil {
+		return 0, fmt.Errorf("count delayed events: %w", err)
+	}
+	return n, nil
+}
+
+// RestartDelayedEvent implements storage.DelayedEventStore.
+func (s *DelayedEvents) RestartDelayedEvent(ctx context.Context, delayID string, nowMS int64) error {
+	res, err := s.db.ExecContext(ctx, s.q(restartDelayedEventSQL), nowMS, nowMS, delayID)
+	if err != nil {
+		return fmt.Errorf("restart delayed event: %w", err)
+	}
+	return oneRow(res)
+}
+
+// FinaliseDelayedEvent implements storage.DelayedEventStore.
+func (s *DelayedEvents) FinaliseDelayedEvent(ctx context.Context, e storage.DelayedEvent) error {
+	res, err := s.db.ExecContext(ctx, s.q(finaliseDelayedEventSQL),
+		e.FinalisedAtMS, e.Outcome, e.Reason, e.EventID, string(e.Error), e.DelayID)
+	if err != nil {
+		return fmt.Errorf("finalise delayed event: %w", err)
+	}
+	return oneRow(res)
+}
+
+func oneRow(res sql.Result) error {
+	n, err := res.RowsAffected()
+	if err != nil {
+		return fmt.Errorf("delayed event: %w", err)
+	}
+	if n == 0 {
+		return storage.ErrNoSuchDelayedEvent
+	}
+	return nil
+}
+
+// DueDelayedEvents implements storage.DelayedEventStore.
+func (s *DelayedEvents) DueDelayedEvents(ctx context.Context, nowMS int64, limit int) ([]storage.DelayedEvent, error) {
+	return s.list(ctx, selectDueDelayedEventsSQL, nowMS, limit)
+}
+
+// NextDelayedEventDue implements storage.DelayedEventStore.
+func (s *DelayedEvents) NextDelayedEventDue(ctx context.Context) (int64, bool, error) {
+	var next sql.NullInt64
+	if err := s.db.QueryRowContext(ctx, s.q(selectNextDelayedEventDueSQL)).Scan(&next); err != nil {
+		return 0, false, fmt.Errorf("next delayed event: %w", err)
+	}
+	return next.Int64, next.Valid, nil
+}
+
+// ScheduledDelayedStateEvents implements storage.DelayedEventStore.
+func (s *DelayedEvents) ScheduledDelayedStateEvents(ctx context.Context, roomID, eventType, stateKey string) ([]storage.DelayedEvent, error) {
+	return s.list(ctx, selectScheduledStateEventsSQL, roomID, eventType, stateKey)
+}
+
+// PurgeFinalisedDelayedEvents implements storage.DelayedEventStore.
+func (s *DelayedEvents) PurgeFinalisedDelayedEvents(ctx context.Context, beforeMS int64) error {
+	if _, err := s.db.ExecContext(ctx, s.q(purgeFinalisedDelayedEventsSQL), beforeMS); err != nil {
+		return fmt.Errorf("purge delayed events: %w", err)
+	}
+	return nil
+}
+
+func (s *DelayedEvents) list(ctx context.Context, query string, args ...any) ([]storage.DelayedEvent, error) {
+	rows, err := s.db.QueryContext(ctx, s.q(query), args...)
+	if err != nil {
+		return nil, fmt.Errorf("read delayed events: %w", err)
+	}
+	defer rows.Close()
+
+	var out []storage.DelayedEvent
+	for rows.Next() {
+		var (
+			e                     storage.DelayedEvent
+			stateKey              sql.NullString
+			content, errorContent string
+		)
+		if err := rows.Scan(&e.DelayID, &e.UserID, &e.DeviceID, &e.RoomID, &e.Type, &stateKey, &content,
+			&e.DelayMS, &e.RunningSinceMS, &e.SendAtMS,
+			&e.FinalisedAtMS, &e.Outcome, &e.Reason, &e.EventID, &errorContent,
+		); err != nil {
+			return nil, fmt.Errorf("read delayed event: %w", err)
+		}
+		if stateKey.Valid {
+			e.StateKey = &stateKey.String
+		}
+		e.Content = []byte(content)
+		if errorContent != "" {
+			e.Error = []byte(errorContent)
+		}
+		out = append(out, e)
+	}
+	return out, rows.Err()
+}
+
+// OpenIDTokens is the shared implementation of storage.OpenIDTokenStore.
+type OpenIDTokens struct {
+	db     *sql.DB
+	rebind func(string) string
+}
+
+// NewOpenIDTokens builds an OpenID token store.
+func NewOpenIDTokens(db *sql.DB, rebind func(string) string) *OpenIDTokens {
+	if rebind == nil {
+		rebind = func(query string) string { return query }
+	}
+	return &OpenIDTokens{db: db, rebind: rebind}
+}
+
+const (
+	insertOpenIDTokenSQL = `
+		INSERT INTO openid_tokens (token_hash, user_id, expires_at_ms) VALUES (?, ?, ?)`
+
+	selectOpenIDTokenSQL = `
+		SELECT user_id FROM openid_tokens WHERE token_hash = ? AND expires_at_ms > ?`
+
+	purgeOpenIDTokensSQL = `DELETE FROM openid_tokens WHERE expires_at_ms < ?`
+)
+
+// InsertOpenIDToken implements storage.OpenIDTokenStore.
+func (s *OpenIDTokens) InsertOpenIDToken(ctx context.Context, tokenHash, userID string, expiresAtMS int64) error {
+	if _, err := s.db.ExecContext(ctx, s.rebind(insertOpenIDTokenSQL), tokenHash, userID, expiresAtMS); err != nil {
+		return fmt.Errorf("insert OpenID token: %w", err)
+	}
+	return nil
+}
+
+// OpenIDTokenUser implements storage.OpenIDTokenStore.
+func (s *OpenIDTokens) OpenIDTokenUser(ctx context.Context, tokenHash string, nowMS int64) (string, error) {
+	var userID string
+	err := s.db.QueryRowContext(ctx, s.rebind(selectOpenIDTokenSQL), tokenHash, nowMS).Scan(&userID)
+	if errors.Is(err, sql.ErrNoRows) {
+		return "", storage.ErrNoSuchOpenIDToken
+	}
+	if err != nil {
+		return "", fmt.Errorf("read OpenID token: %w", err)
+	}
+	return userID, nil
+}
+
+// PurgeOpenIDTokens implements storage.OpenIDTokenStore.
+func (s *OpenIDTokens) PurgeOpenIDTokens(ctx context.Context, beforeMS int64) error {
+	if _, err := s.db.ExecContext(ctx, s.rebind(purgeOpenIDTokensSQL), beforeMS); err != nil {
+		return fmt.Errorf("purge OpenID tokens: %w", err)
+	}
+	return nil
+}
+
+// Compile-time proof that the shared implementations satisfy the interfaces.
+var (
+	_ storage.DelayedEventStore = (*DelayedEvents)(nil)
+	_ storage.OpenIDTokenStore  = (*OpenIDTokens)(nil)
+)
diff --git a/server/internal/storage/sqlstore/sqlstore.go b/server/internal/storage/sqlstore/sqlstore.go
index 290339f..84500c4 100644
--- a/server/internal/storage/sqlstore/sqlstore.go
+++ b/server/internal/storage/sqlstore/sqlstore.go
@@ -69,6 +69,8 @@ type Store struct {
 	push     *Push
 	admin    *Admin
 	apps     *AppServices
+	delayed  *DelayedEvents
+	openID   *OpenIDTokens
 }
 
 // New builds a Store. It does not touch the database.
@@ -93,6 +95,8 @@ func New(opts Options) (*Store, error) {
 		push:     NewPush(opts.DB, opts.Rebind),
 		admin:    NewAdmin(opts.DB, opts.Rebind, opts.IsUniqueViolation),
 		apps:     NewAppServices(opts.DB, opts.Rebind),
+		delayed:  NewDelayedEvents(opts.DB, opts.Rebind),
+		openID:   NewOpenIDTokens(opts.DB, opts.Rebind),
 	}, nil
 }
 
@@ -138,6 +142,12 @@ func (s *Store) Admin() storage.AdminStore { return s.admin }
 // AppServices implements storage.Database.
 func (s *Store) AppServices() storage.AppServiceStore { return s.apps }
 
+// DelayedEvents implements storage.Database.
+func (s *Store) DelayedEvents() storage.DelayedEventStore { return s.delayed }
+
+// OpenIDTokens implements storage.Database.
+func (s *Store) OpenIDTokens() storage.OpenIDTokenStore { return s.openID }
+
 // Migrate implements storage.Database.
 func (s *Store) Migrate(ctx context.Context) error {
 	ms, err := s.migrations()
diff --git a/server/internal/storage/storage.go b/server/internal/storage/storage.go
index 400677e..34762f3 100644
--- a/server/internal/storage/storage.go
+++ b/server/internal/storage/storage.go
@@ -111,6 +111,14 @@ type Database interface {
 	// stream.
 	AppServices() AppServiceStore
 
+	// DelayedEvents is where the delayed events clients scheduled wait
+	// to be sent (MSC4140).
+	DelayedEvents() DelayedEventStore
+
+	// OpenIDTokens is where the OpenID tokens users hand to third parties
+	// are kept.
+	OpenIDTokens() OpenIDTokenStore
+
 	// Close releases the connection pool.
 	Close() error
 }
diff --git a/warp.yaml.example b/warp.yaml.example
index 5770827..772a3c6 100644
--- a/warp.yaml.example
+++ b/warp.yaml.example
@@ -103,9 +103,11 @@ client_api:
   # 0 means no expiry.                WARP_REFRESH_TOKEN_LIFETIME
   refresh_token_lifetime: 0s
 
-  # Relay servers for voice and video calls, handed to clients by
-  # GET /voip/turnServer. With no uris, calls only connect where the two
-  # browsers can reach each other directly (the same network, mostly).
+  # Relay servers for Matrix 1:1 VoIP, handed to clients by
+  # GET /voip/turnServer. Warp's web client doesn't use them: its calls go
+  # through LiveKit (rtc below), which needs no TURN of its own here. This
+  # is for other Matrix clients that still place legacy 1:1 calls; with no
+  # uris, theirs only connect where the two can reach each other directly.
   #
   # With shared_secret (coturn's `use-auth-secret` + `static-auth-secret`)
   # every user gets credentials that expire after user_lifetime. username
@@ -120,6 +122,24 @@ client_api:
     username: ""                  # WARP_TURN_USERNAME
     password: ""                  # WARP_TURN_PASSWORD
 
+  # Group calls (MatrixRTC). Warp carries no call media itself: clients
+  # publish to a LiveKit SFU and get a token for it from the LiveKit JWT
+  # service (lk-jwt-service), which checks who they are with an OpenID
+  # token from this server. Its URL is advertised to clients in
+  # /.well-known/matrix/client; leave it empty for no group calls.
+  # See docs/calls.md.
+  rtc:
+    livekit_service_url: ""       # WARP_RTC_LIVEKIT_SERVICE_URL
+    # e.g. "https://livekit-jwt.example.org"
+
+  # Delayed events (MSC4140): events a client schedules now for the server
+  # to send later unless it pushes them back. A group call member's "left
+  # the call" is one, so someone whose browser crashes still leaves.
+  # max_delay 0 turns them off.
+  delayed_events:
+    max_delay: 24h                # WARP_DELAYED_EVENTS_MAX_DELAY
+    max_per_user: 100             # WARP_DELAYED_EVENTS_MAX_PER_USER
+
   # Per-endpoint rate limiting. Each bucket allows `burst` requests back
   # to back and returns one slot every `interval`, per client address.
   # Login and registration get their own, tighter, buckets because they