feat(crypto): QR-code device verification (alongside emoji SAS)

B2 of the Matrix protocol-gaps roadmap, gate-green (688 tests):
- Enable QR verification methods (show/scan/reciprocate) in initMatrix.
- Extend DeviceVerification: the Ready step offers your own QR (byte-mode encode
  via qrcode), a camera 'Scan their QR code' flow, and an emoji fallback; the
  Started step routes reciprocate → a confirm step (useVerifierShowReciprocateQr)
  or SAS as before.
- New QrScanner component: getUserMedia + jsQR, handing the raw binaryData bytes
  to request.scanQRCode (BarcodeDetector is string-only, so can't be used).
- Adds qrcode + jsqr (small, pure-JS, client-only); build-verified under rolldown.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

LOTUS_TESTING.md

@@ -675,6 +675,12 @@ Run the axe DevTools extension (or Lighthouse → Accessibility) on a room view,
 
 ## Outstanding verification backlog
 
+**QR Device Verification (2026-07):** With two logged-in Lotus sessions (or Lotus + Element), start a device verification. On the **Ready** step you now see your own QR code plus a **"Scan their QR code"** button and a **"Verify with emoji instead"** fallback. Have one device **scan** the other's code (grant camera permission) → the showing device asks you to **Confirm**, and both reach **verified**. Check: emoji-SAS still works unchanged; denying camera shows a graceful "verify with emojis instead" message; a deliberately-wrong scan cancels cleanly. Desktop (WebView2) auto-grants the camera; web needs the Permissions-Policy camera allowance (already set).
+
+**Disappearing Messages (MSC1763 `m.room.retention`, 2026-07):** In Room Settings → General → **Message Retention**, an admin picks Off / 1 Day / 1 Week / 1 Month (non-admins see the buttons disabled). After setting e.g. 1 Day, messages older than a day **vanish from the timeline** for everyone in Lotus (toggle Settings → General → **Show Hidden Events** to reveal them again). Setting back to **Off** restores them. Separately, each user can enable Settings → General → **Enforce Message Retention** (default OFF) → their OWN expired messages then get **permanently redacted** within ~30 s (verify: OTHER people's messages are NEVER redacted by this; only your own). Note true server-side purge also needs Synapse `retention:` configured.
+
+**Mark as Unread + Low Priority (MSC2867 / m.lowpriority, 2026-07):** Right-click a room in the sidebar → **Mark as Unread** puts a dot on the row (bold name) even with no new messages; opening/reading the room clears it, and it syncs to another device. **Mark as Read** on a marked room clears it too. Right-click → **Add to Low Priority** moves the room into a collapsed "Low Priority" category at the bottom of the room list (and removes it from Favorites if it was there, and vice-versa); **Remove from Low Priority** returns it to Rooms.
+
 **Windows rich toast (D6, 2026-07 — desktop/Windows build only):** get a message notification while the desktop app is backgrounded → the toast is attributed to **Lotus Chat** (not "PowerShell"/generic) and shows an inline **reply box + Send**; typing a reply + Send **posts it to that room**; clicking the toast body **opens the room**. Previously these silently fell back to a plain toast (no reply/click). If it still falls back, check that a `Lotus Chat.lnk` exists in the Start-Menu Programs folder.
 
 **Invite QR is now generated LOCALLY (2026-07):** Room settings → Share Room → the QR code renders (a black-on-white SVG in a white box) with **no network request** to `api.qrserver.com` (check DevTools Network — there should be no external QR fetch, and it should work offline / behind strict CSP). **Scan it** with a phone camera / Matrix app → it opens the correct `matrix.to` room-invite link. (`api.qrserver.com` was removed from the prod CSP img-src, so a regression would make the QR blank rather than silently phone home.)

LOTUS_TODO.md

@@ -91,6 +91,29 @@ Observed live in prod 2026-06-30 during a 2-person **Element Call** (E2EE). Thes
 
 ---
 
+## 🌐 Matrix Protocol Gaps
+
+Genuine Matrix client-spec / MSC features Lotus does **not** yet implement (audited 2026-07 against the codebase — almost everything else is built: pinning, stickers+picker, room directory, mutual rooms MSC2666, blurhash, key backup/recovery/SSSS, SAS verification, ignore list, invite spam-filter, voice messages, polls, threads, spaces, OIDC, extended profiles, delayed events, authed media). Build each **fully** — spec-correct events, native-Cinny folds UI, tests. Order = clean wins first.
+
+**Phase A ✅ (2026-07, gate-green 683 tests):**
+
+- [x] **Mark as Unread — MSC2867 `m.marked_unread`.** Room account data `{ unread: true }` (+ unstable `com.famedly.marked_unread`) via `mx.setRoomAccountData`; clear on read. Context-menu item in `RoomNavItem` + light the existing unread dot; integrate `state/room/roomToUnread.ts`.
+- [x] **Low Priority rooms — `m.lowpriority` tag.** Mirror the favourite impl (`RoomNavItem.tsx:331-337` `setRoomTag/deleteRoomTag` + the favourites category in `home/Home.tsx`): context-menu toggle + a collapsed "Low Priority" category sorted to the bottom, excluded from normal unread nudging.
+
+**Phase B ✅ (2026-07, gate-green 688 tests):**
+
+- [x] **Disappearing Messages — MSC1763 `m.room.retention`.** PL-gated room-settings `SettingTile` to set `{ max_lifetime }`; retention badge; a client-side sweep hides/self-redacts own expired events (pattern like the mute-timer restore in `ClientNonUIFeatures.tsx`). True server deletion also wants Synapse `retention:` (LXC 151).
+- [x] **QR Device Verification — reciprocate QR.** Add the QR path beside emoji-SAS in `components/DeviceVerification.tsx`: render with `qrcode.react` (already a dep), scan via `BarcodeDetector` (fallback `jsQR`); uses the SDK `VerificationRequest` QR/reciprocate support.
+
+**Phase C (large — each its own planning session):**
+
+- [ ] **Room Widgets — MSC1236 + widget API.** No general widget UI exists (only the PL entry `im.vector.modular.widgets`; the EC call widget is hardcoded). Read `im.vector.modular.widgets`/`m.widget` state, add an Add/Manage panel + sandboxed iframe renderer via `matrix-widget-api` — **extend the existing EC widget plumbing** (`plugins/call/CallEmbed.ts`). Enables Etherpad/notes/dashboards/integrations.
+- [ ] **Sliding Sync — MSC3575 / simplified MSC4186.** Lotus is on **legacy full `/sync`** though the server advertises `simplified_msc3575`. matrix-js-sdk ships `SlidingSync`; migration → near-instant cold start + low memory + huge-account scale. Touches the sync/room-list/spaces/unread core — behind a feature flag with a legacy fallback. **Plan separately before touching.**
+
+**Server-gated / advanced (capture, don't build yet):** QR sign-in for a new device (**MSC4108** rendezvous — needs an HS-side endpoint); dehydrated devices (**MSC3814** — offline key delivery, also helps the E2EE KE cluster); E2EE history key sharing on invite (**MSC3061** `shared_history`, niche); voice broadcast (Element MSC3888, low value — skip).
+
+---
+
 ## 📋 Open Feature Backlog
 
 ### [ ] P4-4 · Math / LaTeX Rendering (LOW PRIORITY)

package-lock.json

@@ -49,6 +49,7 @@
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@@ -10500,6 +10543,15 @@
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@@ -10768,6 +10845,124 @@
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package.json

@@ -74,6 +74,7 @@
     "immer": "11.1.8",
     "is-hotkey": "0.2.0",
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@@ -82,6 +83,7 @@
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@@ -112,6 +114,7 @@
     "@types/katex": "0.16.8",
     "@types/node": "25.9.1",
     "@types/prismjs": "1.26.6",
+    "@types/qrcode": "1.5.6",
     "@types/react": "19.2.15",
     "@types/react-dom": "19.2.3",
     "@types/react-google-recaptcha": "2.1.9",

src/app/components/DeviceVerification.tsx

@@ -1,12 +1,14 @@
 import {
+  ShowQrCodeCallbacks,
   ShowSasCallbacks,
   VerificationPhase,
   VerificationRequest,
   Verifier,
 } from 'matrix-js-sdk/lib/crypto-api';
-import React, { CSSProperties, useCallback, useEffect, useState } from 'react';
+import React, { CSSProperties, useCallback, useEffect, useRef, useState } from 'react';
 import { useTranslation } from 'react-i18next';
 import { VerificationMethod } from 'matrix-js-sdk/lib/types';
+import QRCode from 'qrcode';
 import {
   Box,
   Button,
@@ -27,11 +29,13 @@ import {
   useVerificationRequestPhase,
   useVerificationRequestReceived,
   useVerifierCancel,
+  useVerifierShowReciprocateQr,
   useVerifierShowSas,
 } from '../hooks/useVerificationRequest';
 import { AsyncStatus, useAsyncCallback } from '../hooks/useAsyncCallback';
 import { ContainerColor } from '../styles/ContainerColor.css';
 import { useModalStyle } from '../hooks/useModalStyle';
+import { QrScanner } from './QrScanner';
 
 const DialogHeaderStyles: CSSProperties = {
   padding: `0 ${config.space.S200} 0 ${config.space.S400}`,
@@ -97,32 +101,6 @@ function VerificationAccept({ onAccept }: VerificationAcceptProps) {
   );
 }
 
-function VerificationWaitStart() {
-  const { t } = useTranslation();
-  return (
-    <Box direction="Column" gap="400">
-      <Text>{t('Organisms.DeviceVerification.request_accepted')}</Text>
-      <WaitingMessage message={t('Organisms.DeviceVerification.waiting_response')} />
-    </Box>
-  );
-}
-
-type VerificationStartProps = {
-  onStart: () => Promise<void>;
-};
-function AutoVerificationStart({ onStart }: VerificationStartProps) {
-  const { t } = useTranslation();
-  useEffect(() => {
-    onStart();
-  }, [onStart]);
-
-  return (
-    <Box direction="Column" gap="400">
-      <WaitingMessage message={t('Organisms.DeviceVerification.starting_emoji')} />
-    </Box>
-  );
-}
-
 function CompareEmoji({ sasData }: { sasData: ShowSasCallbacks }) {
   const { t } = useTranslation();
   const [confirmState, confirm] = useAsyncCallback(useCallback(() => sasData.confirm(), [sasData]));
@@ -237,6 +215,120 @@ function VerificationCanceled({ onClose }: VerificationCanceledProps) {
   );
 }
 
+function QrCodeImage({ data }: { data: Uint8ClampedArray }) {
+  const canvasRef = useRef<HTMLCanvasElement>(null);
+  useEffect(() => {
+    const canvas = canvasRef.current;
+    if (!canvas) return;
+    // Byte-mode so the raw verification bytes round-trip (a string value would
+    // mangle high bytes via UTF-8).
+    QRCode.toCanvas(canvas, [{ data: new Uint8Array(data), mode: 'byte' }], {
+      width: 220,
+      margin: 2,
+      color: { dark: '#000000', light: '#ffffff' },
+    }).catch(() => undefined);
+  }, [data]);
+  return (
+    <Box justifyContent="Center">
+      <canvas ref={canvasRef} style={{ borderRadius: config.radii.R300 }} />
+    </Box>
+  );
+}
+
+type VerificationReadyProps = {
+  request: VerificationRequest;
+  onStartSas: () => void;
+  onScanned: (bytes: Uint8ClampedArray) => void;
+};
+function VerificationReady({ request, onStartSas, onScanned }: VerificationReadyProps) {
+  const [myQr, setMyQr] = useState<Uint8ClampedArray>();
+  const [scanning, setScanning] = useState(false);
+  const canShowMine = request.otherPartySupportsMethod(VerificationMethod.ScanQrCode);
+  const canScanTheirs = request.otherPartySupportsMethod(VerificationMethod.ShowQrCode);
+
+  useEffect(() => {
+    if (!canShowMine) return;
+    request
+      .generateQRCode()
+      .then((bytes) => {
+        if (bytes) setMyQr(bytes);
+      })
+      .catch(() => undefined);
+  }, [request, canShowMine]);
+
+  if (scanning) {
+    return <QrScanner onScan={onScanned} onCancel={() => setScanning(false)} />;
+  }
+
+  return (
+    <Box direction="Column" gap="400">
+      {myQr && (
+        <Box direction="Column" gap="200">
+          <Text size="T300">Scan this code with your other device to verify.</Text>
+          <QrCodeImage data={myQr} />
+        </Box>
+      )}
+      <Box direction="Column" gap="200">
+        {canScanTheirs && (
+          <Button variant="Primary" fill="Solid" onClick={() => setScanning(true)}>
+            <Text size="B400">Scan their QR code</Text>
+          </Button>
+        )}
+        <Button variant="Secondary" fill="Soft" onClick={onStartSas}>
+          <Text size="B400">Verify with emoji instead</Text>
+        </Button>
+      </Box>
+    </Box>
+  );
+}
+
+type ReciprocateVerificationProps = {
+  verifier: Verifier;
+  onCancel: () => void;
+};
+function ReciprocateVerification({ verifier, onCancel }: ReciprocateVerificationProps) {
+  const [qrCallbacks, setQrCallbacks] = useState<ShowQrCodeCallbacks>();
+  const [confirmState, confirm] = useAsyncCallback(
+    useCallback(async () => qrCallbacks?.confirm(), [qrCallbacks]),
+  );
+
+  useVerifierShowReciprocateQr(verifier, setQrCallbacks);
+  useVerifierCancel(verifier, onCancel);
+
+  const confirming =
+    confirmState.status === AsyncStatus.Loading || confirmState.status === AsyncStatus.Success;
+
+  // The showing side gets ShowReciprocateQr callbacks after the other device
+  // scans; the scanning side never does (it already called verify()) and just
+  // waits for completion.
+  if (!qrCallbacks) {
+    return (
+      <Box direction="Column" gap="400">
+        <WaitingMessage message="Verifying…" />
+      </Box>
+    );
+  }
+
+  return (
+    <Box direction="Column" gap="400">
+      <Text>The other device scanned this code. Confirm it now shows as verified.</Text>
+      <Box direction="Column" gap="200">
+        <Button variant="Primary" fill="Soft" onClick={confirm} disabled={confirming}>
+          <Text size="B400">Confirm</Text>
+        </Button>
+        <Button
+          variant="Primary"
+          fill="Soft"
+          onClick={() => qrCallbacks.cancel()}
+          disabled={confirming}
+        >
+          <Text size="B400">Cancel</Text>
+        </Button>
+      </Box>
+    </Box>
+  );
+}
+
 type DeviceVerificationProps = {
   request: VerificationRequest;
   onExit: () => void;
@@ -256,6 +348,17 @@ export function DeviceVerification({ request, onExit }: DeviceVerificationProps)
   const handleStart = useCallback(async () => {
     await request.startVerification(VerificationMethod.Sas);
   }, [request]);
+  const handleScanned = useCallback(
+    async (bytes: Uint8ClampedArray) => {
+      try {
+        const verifier = await request.scanQRCode(bytes);
+        await verifier.verify();
+      } catch {
+        // A bad/mismatched scan cancels the request; the Cancelled phase renders.
+      }
+    },
+    [request],
+  );
 
   return (
     <Overlay open backdrop={<OverlayBackdrop />}>
@@ -290,15 +393,20 @@ export function DeviceVerification({ request, onExit }: DeviceVerificationProps)
                 ) : (
                   <VerificationAccept onAccept={handleAccept} />
                 ))}
-              {phase === VerificationPhase.Ready &&
+              {phase === VerificationPhase.Ready && (
-                (request.initiatedByMe ? (
+                <VerificationReady
-                  <AutoVerificationStart onStart={handleStart} />
+                  request={request}
-                ) : (
+                  onStartSas={handleStart}
-                  <VerificationWaitStart />
+                  onScanned={handleScanned}
-                ))}
+                />
+              )}
               {phase === VerificationPhase.Started &&
                 (request.verifier ? (
-                  <SasVerification verifier={request.verifier} onCancel={handleCancel} />
+                  request.chosenMethod === VerificationMethod.Reciprocate ? (
+                    <ReciprocateVerification verifier={request.verifier} onCancel={handleCancel} />
+                  ) : (
+                    <SasVerification verifier={request.verifier} onCancel={handleCancel} />
+                  )
                 ) : (
                   <VerificationUnexpected
                     message="Unexpected Error! Verification is started but verifier is missing."

src/app/components/QrScanner.tsx

@@ -0,0 +1,101 @@
+import React, { useEffect, useRef, useState } from 'react';
+import { Box, Button, color, config, Text } from 'folds';
+import jsQR from 'jsqr';
+
+type QrScannerProps = {
+  onScan: (bytes: Uint8ClampedArray) => void;
+  onCancel: () => void;
+};
+
+// Camera QR scanner. Decodes frames with jsQR and hands back the raw byte
+// segment (`result.binaryData`) — Matrix QR verification needs the raw bytes,
+// not a decoded string, so the string-only `BarcodeDetector` can't be used.
+export function QrScanner({ onScan, onCancel }: QrScannerProps) {
+  const videoRef = useRef<HTMLVideoElement>(null);
+  const [error, setError] = useState<string>();
+  const doneRef = useRef(false);
+
+  useEffect(() => {
+    let stream: MediaStream | undefined;
+    let raf = 0;
+    const canvas = document.createElement('canvas');
+    const ctx = canvas.getContext('2d', { willReadFrequently: true });
+
+    const tick = () => {
+      const video = videoRef.current;
+      if (!doneRef.current && video && ctx && video.readyState === video.HAVE_ENOUGH_DATA) {
+        canvas.width = video.videoWidth;
+        canvas.height = video.videoHeight;
+        ctx.drawImage(video, 0, 0, canvas.width, canvas.height);
+        const image = ctx.getImageData(0, 0, canvas.width, canvas.height);
+        const result = jsQR(image.data, image.width, image.height);
+        if (result && result.binaryData.length > 0) {
+          doneRef.current = true;
+          onScan(new Uint8ClampedArray(result.binaryData));
+          return;
+        }
+      }
+      raf = requestAnimationFrame(tick);
+    };
+
+    (async () => {
+      try {
+        stream = await navigator.mediaDevices.getUserMedia({
+          video: { facingMode: 'environment' },
+        });
+        if (videoRef.current) {
+          videoRef.current.srcObject = stream;
+          await videoRef.current.play();
+        }
+        raf = requestAnimationFrame(tick);
+      } catch {
+        setError(
+          'Could not access the camera. Grant camera permission, or verify with emojis instead.',
+        );
+      }
+    })();
+
+    return () => {
+      doneRef.current = true;
+      cancelAnimationFrame(raf);
+      stream?.getTracks().forEach((track) => track.stop());
+    };
+  }, [onScan]);
+
+  if (error) {
+    return (
+      <Box direction="Column" gap="400">
+        <Text style={{ color: color.Critical.Main }} size="T300">
+          {error}
+        </Text>
+        <Button variant="Secondary" fill="Soft" onClick={onCancel}>
+          <Text size="B400">Back</Text>
+        </Button>
+      </Box>
+    );
+  }
+
+  return (
+    <Box direction="Column" gap="400" alignItems="Center">
+      <Text size="T300" align="Center">
+        Point your camera at the QR code shown on your other device.
+      </Text>
+      <video
+        ref={videoRef}
+        muted
+        playsInline
+        style={{
+          width: '100%',
+          maxWidth: 280,
+          borderRadius: config.radii.R400,
+          background: '#000',
+        }}
+      >
+        <track kind="captions" />
+      </video>
+      <Button variant="Secondary" fill="Soft" onClick={onCancel}>
+        <Text size="B400">Cancel</Text>
+      </Button>
+    </Box>
+  );
+}

src/app/features/common-settings/general/RoomRetention.tsx

@@ -0,0 +1,80 @@
+import React, { useCallback } from 'react';
+import { Box, Button, color, Spinner, Text } from 'folds';
+import { MatrixError } from 'matrix-js-sdk';
+import { SequenceCard } from '../../../components/sequence-card';
+import { SequenceCardStyle } from '../../room-settings/styles.css';
+import { SettingTile } from '../../../components/setting-tile';
+import { useMatrixClient } from '../../../hooks/useMatrixClient';
+import { useRoom } from '../../../hooks/useRoom';
+import { StateEvent } from '../../../../types/matrix/room';
+import { AsyncStatus, useAsyncCallback } from '../../../hooks/useAsyncCallback';
+import { useStateEvent } from '../../../hooks/useStateEvent';
+import { RoomPermissionsAPI } from '../../../hooks/useRoomPermissions';
+import { RetentionContent, RETENTION_PRESETS } from '../../../utils/retention';
+
+type RoomRetentionProps = {
+  permissions: RoomPermissionsAPI;
+};
+export function RoomRetention({ permissions }: RoomRetentionProps) {
+  const mx = useMatrixClient();
+  const room = useRoom();
+
+  const canEdit = permissions.stateEvent(StateEvent.RoomRetention, mx.getSafeUserId());
+
+  const event = useStateEvent(room, StateEvent.RoomRetention);
+  const currentMs = event?.getContent<RetentionContent>().max_lifetime ?? 0;
+
+  const [submitState, submit] = useAsyncCallback(
+    useCallback(
+      async (ms: number) => {
+        const content: RetentionContent = ms > 0 ? { max_lifetime: ms } : {};
+        // Lotus custom-state convention: cast the type key (RoomRetention isn't a
+        // typed key in the SDK's StateEvents map).
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        await mx.sendStateEvent(room.roomId, StateEvent.RoomRetention as any, content);
+      },
+      [mx, room.roomId],
+    ),
+  );
+  const submitting = submitState.status === AsyncStatus.Loading;
+
+  return (
+    <SequenceCard
+      className={SequenceCardStyle}
+      variant="SurfaceVariant"
+      direction="Column"
+      gap="400"
+    >
+      <SettingTile
+        title="Message Retention"
+        description="Messages older than this window disappear from the timeline. Each member can opt in to permanently delete their own expired messages in Settings → General; full server-side deletion also requires homeserver retention to be configured."
+      >
+        <Box gap="200" alignItems="Center" style={{ flexWrap: 'wrap' }}>
+          {RETENTION_PRESETS.map((preset) => {
+            const active = currentMs === preset.ms;
+            return (
+              <Button
+                key={preset.label}
+                type="button"
+                size="300"
+                variant={active ? 'Primary' : 'Secondary'}
+                fill={active ? 'Solid' : 'Soft'}
+                radii="300"
+                disabled={!canEdit || submitting}
+                onClick={() => submit(preset.ms)}
+              >
+                <Text size="B300">{preset.label}</Text>
+              </Button>
+            );
+          })}
+          {submitting && <Spinner size="100" variant="Secondary" />}
+        </Box>
+        {submitState.status === AsyncStatus.Error && (
+          <Text style={{ color: color.Critical.Main }} size="T200">
+            {(submitState.error as MatrixError).message}
+          </Text>
+        )}
+      </SettingTile>
+    </SequenceCard>
+  );
+}

src/app/features/common-settings/general/index.ts

@@ -5,6 +5,7 @@ export * from './RoomJoinRules';
 export * from './RoomProfile';
 export * from './RoomPublish';
 export * from './RoomQuality';
+export * from './RoomRetention';
 export * from './RoomShareInvite';
 export * from './RoomUpgrade';
 export * from './RoomVoiceLimit';

src/app/features/room-nav/RoomNavItem.tsx

@@ -38,6 +38,7 @@ import { nameInitials } from '../../utils/common';
 import { useMatrixClient } from '../../hooks/useMatrixClient';
 import { useRoomUnread } from '../../state/hooks/unread';
 import { roomToUnreadAtom } from '../../state/room/roomToUnread';
+import { markedUnreadAtom, setMarkedUnread } from '../../state/room/markedUnread';
 import { getPowersLevelFromMatrixEvent, usePowerLevels } from '../../hooks/usePowerLevels';
 import { markAsRead } from '../../utils/notifications';
 import { UseStateProvider } from '../../components/UseStateProvider';
@@ -329,18 +330,39 @@ const RoomNavItemMenu = forwardRef<HTMLDivElement, RoomNavItemMenuProps>(
     const isServerNotice = room.getType() === 'm.server_notice';
 
     const isFavorite = !!room.tags?.['m.favourite'];
+    const isLowPriority = !!room.tags?.['m.lowpriority'];
 
     const handleToggleFavorite = () => {
       if (isFavorite) {
         mx.deleteRoomTag(room.roomId, 'm.favourite');
       } else {
+        // Favourite and low-priority are mutually exclusive.
+        if (isLowPriority) mx.deleteRoomTag(room.roomId, 'm.lowpriority');
         mx.setRoomTag(room.roomId, 'm.favourite', { order: 0.5 });
       }
       requestClose();
     };
 
+    const handleToggleLowPriority = () => {
+      if (isLowPriority) {
+        mx.deleteRoomTag(room.roomId, 'm.lowpriority');
+      } else {
+        if (isFavorite) mx.deleteRoomTag(room.roomId, 'm.favourite');
+        mx.setRoomTag(room.roomId, 'm.lowpriority', { order: 0.5 });
+      }
+      requestClose();
+    };
+
+    const markedUnread = useAtomValue(markedUnreadAtom).has(room.roomId);
+
     const handleMarkAsRead = () => {
       markAsRead(mx, room.roomId, hideActivity);
+      if (markedUnread) setMarkedUnread(mx, room.roomId, false).catch(() => undefined);
+      requestClose();
+    };
+
+    const handleMarkAsUnread = () => {
+      setMarkedUnread(mx, room.roomId, true).catch(() => undefined);
       requestClose();
     };
 
@@ -393,12 +415,23 @@ const RoomNavItemMenu = forwardRef<HTMLDivElement, RoomNavItemMenuProps>(
             size="300"
             after={<Icon size="100" src={Icons.CheckTwice} />}
             radii="300"
-            disabled={!unread}
+            disabled={!unread && !markedUnread}
           >
             <Text style={{ flexGrow: 1 }} as="span" size="T300" truncate>
               Mark as Read
             </Text>
           </MenuItem>
+          <MenuItem
+            onClick={handleMarkAsUnread}
+            size="300"
+            after={<Icon size="100" src={Icons.MessageUnread} />}
+            radii="300"
+            disabled={!!unread || markedUnread}
+          >
+            <Text style={{ flexGrow: 1 }} as="span" size="T300" truncate>
+              Mark as Unread
+            </Text>
+          </MenuItem>
           <RoomNotificationModeSwitcher roomId={room.roomId} value={notificationMode}>
             {(handleOpen, opened, changing) => (
               <MenuItem
@@ -493,6 +526,17 @@ const RoomNavItemMenu = forwardRef<HTMLDivElement, RoomNavItemMenuProps>(
               {isFavorite ? 'Remove from Favorites' : 'Add to Favorites'}
             </Text>
           </MenuItem>
+          <MenuItem
+            onClick={handleToggleLowPriority}
+            size="300"
+            after={<Icon size="100" src={Icons.ChevronBottom} />}
+            radii="300"
+            aria-pressed={isLowPriority}
+          >
+            <Text style={{ flexGrow: 1 }} as="span" size="T300" truncate>
+              {isLowPriority ? 'Remove from Low Priority' : 'Add to Low Priority'}
+            </Text>
+          </MenuItem>
           <MenuItem
             onClick={handleInvite}
             variant="Primary"
@@ -610,6 +654,10 @@ function RoomNavItem_({
   const [menuAnchor, setMenuAnchor] = useState<RectCords>();
   const [renameDialog, setRenameDialog] = useState(false);
   const unread = useRoomUnread(room.roomId, roomToUnreadAtom);
+  // MSC2867: an explicit "mark as unread" lights the row even with no unread
+  // count. `hasUnread` drives the bold name / icon emphasis below.
+  const markedUnread = useAtomValue(markedUnreadAtom).has(room.roomId);
+  const hasUnread = !!unread || markedUnread;
   const typingMember = useRoomTypingMember(room.roomId).filter(
     (receipt) => receipt.userId !== mx.getUserId(),
   );
@@ -692,7 +740,7 @@ function RoomNavItem_({
     <NavItem
       variant="Background"
       radii="400"
-      highlight={unread !== undefined}
+      highlight={hasUnread}
       aria-selected={selected}
       data-hover={!!menuAnchor}
       onContextMenu={handleContextMenu}
@@ -721,7 +769,7 @@ function RoomNavItem_({
               ) : (
                 <RoomIcon
                   style={{
-                    opacity: unread ? config.opacity.P500 : config.opacity.P300,
+                    opacity: hasUnread ? config.opacity.P500 : config.opacity.P300,
                   }}
                   filled={selected}
                   size="100"
@@ -732,7 +780,7 @@ function RoomNavItem_({
             </Avatar>
             <Box as="span" direction="Column" grow="Yes" style={{ minWidth: 0 }}>
               <Box as="span" grow="Yes" alignItems="Center" gap="100">
-                <Text priority={unread ? '500' : '300'} as="span" size="Inherit" truncate>
+                <Text priority={hasUnread ? '500' : '300'} as="span" size="Inherit" truncate>
                   {roomName}
                 </Text>
                 {hasLocalName && (
@@ -773,7 +821,7 @@ function RoomNavItem_({
                 </Box>
               )}
             </Box>
-            {!optionsVisible && !unread && !selected && typingMember.length > 0 && (
+            {!optionsVisible && !hasUnread && !selected && typingMember.length > 0 && (
               <Badge size="300" variant="Secondary" fill="Soft" radii="Pill" outlined>
                 <TypingIndicator size="300" disableAnimation />
               </Badge>
@@ -783,6 +831,11 @@ function RoomNavItem_({
                 <UnreadBadge highlight={unread.highlight > 0} count={unread.total} />
               </UnreadBadgeCenter>
             )}
+            {!optionsVisible && !unread && markedUnread && (
+              <UnreadBadgeCenter>
+                <UnreadBadge highlight={false} count={0} />
+              </UnreadBadgeCenter>
+            )}
             {!optionsVisible && notificationMode !== RoomNotificationMode.Unset && (
               <Icon
                 size="50"

src/app/features/room-settings/general/General.tsx

@@ -12,6 +12,7 @@ import {
   RoomPublishedAddresses,
   RoomPublish,
   RoomQuality,
+  RoomRetention,
   RoomShareInvite,
   RoomUpgrade,
   RoomVoiceLimit,
@@ -56,6 +57,10 @@ export function General({ requestClose }: GeneralProps) {
                 <RoomEncryption permissions={permissions} />
                 <RoomPublish permissions={permissions} />
               </Box>
+              <Box direction="Column" gap="100">
+                <Text size="L400">Message Retention</Text>
+                <RoomRetention permissions={permissions} />
+              </Box>
               <Box direction="Column" gap="100">
                 <Text size="L400">Voice</Text>
                 <RoomVoiceLimit permissions={permissions} />

src/app/features/room/RoomTimeline.tsx

@@ -109,6 +109,8 @@ import { roomIdToActiveThreadIdAtomFamily } from '../../state/room/thread';
 import { ThreadSummary } from './thread/ThreadSummary';
 import { usePowerLevelsContext } from '../../hooks/usePowerLevels';
 import { GetContentCallback, MessageEvent, StateEvent } from '../../../types/matrix/room';
+import { useStateEvent } from '../../hooks/useStateEvent';
+import { RetentionContent, isExpired } from '../../utils/retention';
 import { useKeyDown } from '../../hooks/useKeyDown';
 import { useDocumentFocusChange } from '../../hooks/useDocumentFocusChange';
 import { RenderMessageContent } from '../../components/RenderMessageContent';
@@ -468,6 +470,11 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
   const [encUrlPreview] = useSetting(settingsAtom, 'encUrlPreview');
   const showUrlPreview = room.hasEncryptionStateEvent() ? encUrlPreview : urlPreview;
   const [showHiddenEvents] = useSetting(settingsAtom, 'showHiddenEvents');
+  // MSC1763 retention: messages older than this window are hidden from the
+  // timeline (unless "show hidden events" is on). Reactive so a policy change
+  // re-renders. `undefined` = no policy.
+  const retentionEvent = useStateEvent(room, StateEvent.RoomRetention);
+  const retentionMs = retentionEvent?.getContent<RetentionContent>().max_lifetime;
   const [showDeveloperTools] = useSetting(settingsAtom, 'developerTools');
   const [lotusTerminal] = useSetting(settingsAtom, 'lotusTerminal');
 
@@ -2043,6 +2050,11 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
     if (eventSender && ignoredUsersSet.has(eventSender)) {
       return null;
     }
+    // MSC1763: hide messages past the room's retention window (disappearing
+    // messages). Power users can still inspect via "show hidden events".
+    if (retentionMs && !showHiddenEvents && isExpired(mEvent.getTs(), retentionMs, Date.now())) {
+      return null;
+    }
     if (mEvent.isRedacted() && !showHiddenEvents) {
       // eslint-disable-next-line @typescript-eslint/no-shadow
       const t = mEvent.getType();

src/app/features/settings/general/General.tsx

@@ -2251,6 +2251,10 @@ function Messages() {
   const [urlPreview, setUrlPreview] = useSetting(settingsAtom, 'urlPreview');
   const [encUrlPreview, setEncUrlPreview] = useSetting(settingsAtom, 'encUrlPreview');
   const [showHiddenEvents, setShowHiddenEvents] = useSetting(settingsAtom, 'showHiddenEvents');
+  const [enforceRetentionLocally, setEnforceRetentionLocally] = useSetting(
+    settingsAtom,
+    'enforceRetentionLocally',
+  );
 
   return (
     <Box direction="Column" gap="100">
@@ -2348,6 +2352,19 @@ function Messages() {
           }
         />
       </SequenceCard>
+      <SequenceCard className={SequenceCardStyle} variant="SurfaceVariant" direction="Column">
+        <SettingTile
+          title="Enforce Message Retention"
+          description="Permanently delete your own messages once a room's retention window (Room Settings → Message Retention) has passed. Off by default; only affects your own messages."
+          after={
+            <Switch
+              variant="Primary"
+              value={enforceRetentionLocally}
+              onChange={setEnforceRetentionLocally}
+            />
+          }
+        />
+      </SequenceCard>
     </Box>
   );
 }

src/app/pages/client/ClientNonUIFeatures.tsx

@@ -48,6 +48,7 @@ import { STATUS_EXPIRY_KEY, STATUS_MSG_KEY } from '../../features/settings/accou
 import { useDeepLinkNavigate } from '../../hooks/useDeepLinkNavigate';
 import { toastQueueAtom } from '../../state/toast';
 import { useReminders } from '../../hooks/useReminders';
+import { getRoomRetentionMs, isExpired } from '../../utils/retention';
 import { useTauriUpdater } from '../../hooks/useTauriUpdater';
 import { TauriDesktopFeatures } from '../../components/TauriDesktopFeatures';
 import { KeyboardShortcutsDialog, useKeyboardShortcutsTrigger } from '../../features/shortcuts';
@@ -687,6 +688,62 @@ function ReminderMonitor() {
   return null;
 }
 
+// MSC1763: opt-in local enforcement of room retention. When enabled, permanently
+// redacts the user's OWN messages once a room's retention window passes. Own-only
+// (no redact PL needed); scoped to loaded live-timeline events; dedupes in-flight
+// redactions and retries on the next tick. Default-off, so nothing auto-deletes
+// unless the user turns it on.
+function RetentionSweeper() {
+  const mx = useMatrixClient();
+  const [enforceRetentionLocally] = useSetting(settingsAtom, 'enforceRetentionLocally');
+  const enabledRef = useRef(enforceRetentionLocally);
+  enabledRef.current = enforceRetentionLocally;
+  const redactingRef = useRef<Set<string>>(new Set());
+
+  useEffect(() => {
+    const check = () => {
+      if (!enabledRef.current) return;
+      const myId = mx.getUserId();
+      if (!myId) return;
+      const now = Date.now();
+      mx.getRooms().forEach((room) => {
+        const maxLifetime = getRoomRetentionMs(room);
+        if (!maxLifetime) return;
+        room
+          .getLiveTimeline()
+          .getEvents()
+          .forEach((ev) => {
+            const evId = ev.getId();
+            if (!evId || ev.getSender() !== myId) return;
+            if (ev.isState() || ev.isRedacted() || ev.isSending()) return;
+            const t = ev.getType();
+            // Only actual messages — never our membership/topic/reactions.
+            if (t !== 'm.room.message' && t !== 'm.room.encrypted' && t !== 'm.sticker') return;
+            if (!isExpired(ev.getTs(), maxLifetime, now)) return;
+            if (redactingRef.current.has(evId)) return;
+            redactingRef.current.add(evId);
+            mx.redactEvent(room.roomId, evId, undefined, { reason: 'expired' }).catch(() => {
+              redactingRef.current.delete(evId);
+            });
+          });
+      });
+    };
+
+    check();
+    const interval = setInterval(check, 30_000);
+    const onVisible = () => {
+      if (document.visibilityState === 'visible') check();
+    };
+    document.addEventListener('visibilitychange', onVisible);
+    return () => {
+      clearInterval(interval);
+      document.removeEventListener('visibilitychange', onVisible);
+    };
+  }, [mx]);
+
+  return null;
+}
+
 const TAURI_UPDATE_CHECK_INTERVAL = 12 * 60 * 60_000; // 12 hours
 const TAURI_UPDATE_LAST_CHECK_KEY = 'lotus.tauriUpdateLastCheck';
 
@@ -773,6 +830,7 @@ export function ClientNonUIFeatures({ children }: ClientNonUIFeaturesProps) {
       <InviteNotifications />
       <MessageNotifications />
       <ReminderMonitor />
+      <RetentionSweeper />
       <TauriUpdateFeature />
       <TauriDesktopFeatures />
       <LotusDenoiseFeature />

src/app/pages/client/home/Home.tsx

@@ -223,6 +223,7 @@ const factoryRoomIdByUnread =
 
 const DEFAULT_CATEGORY_ID = makeNavCategoryId('home', 'room');
 const FAVORITES_CATEGORY_ID = makeNavCategoryId('home', 'favorite');
+const LOW_PRIORITY_CATEGORY_ID = makeNavCategoryId('home', 'lowpriority');
 export function Home() {
   const mx = useMatrixClient();
   useNavToActivePathMapper('home');
@@ -261,18 +262,21 @@ export function Home() {
   const roomToUnread = useAtomValue(roomToUnreadAtom);
   const [sortMenuAnchor, setSortMenuAnchor] = useState<RectCords>();
 
-  const { favoriteRooms, otherRooms } = useMemo(() => {
+  const { favoriteRooms, lowPriorityRooms, otherRooms } = useMemo(() => {
     const favs: string[] = [];
+    const low: string[] = [];
     const others: string[] = [];
     rooms.forEach((rId) => {
       const room = mx.getRoom(rId);
       if (room?.tags?.['m.favourite']) {
         favs.push(rId);
+      } else if (room?.tags?.['m.lowpriority']) {
+        low.push(rId);
       } else {
         others.push(rId);
       }
     });
-    return { favoriteRooms: favs, otherRooms: others };
+    return { favoriteRooms: favs, lowPriorityRooms: low, otherRooms: others };
   }, [mx, rooms]);
 
   const sortedFavoriteRooms = useMemo(() => {
@@ -297,6 +301,28 @@ export function Home() {
     });
   }, [mx, sortedFavoriteRooms, filterQuery]);
 
+  const sortedLowPriorityRooms = useMemo(() => {
+    const isClosed = closedCategories.has(LOW_PRIORITY_CATEGORY_ID);
+    const items = Array.from(lowPriorityRooms).sort(
+      isClosed ? factoryRoomIdByActivity(mx) : factoryRoomIdByAtoZ(mx),
+    );
+    if (isClosed) {
+      return items.filter((rId) => roomsWithUnreadSet.has(rId) || rId === selectedRoomId);
+    }
+    return items;
+  }, [mx, lowPriorityRooms, closedCategories, roomsWithUnreadSet, selectedRoomId]);
+
+  const filteredLowPriorityRooms = useMemo(() => {
+    if (!filterQuery.trim()) return sortedLowPriorityRooms;
+    const query = filterQuery.toLowerCase();
+    const localNames = getLocalRoomNamesContent(mx);
+    return sortedLowPriorityRooms.filter((rId) => {
+      const localName = localNames.rooms[rId];
+      const matrixName = mx.getRoom(rId)?.name ?? '';
+      return (localName ?? matrixName).toLowerCase().includes(query);
+    });
+  }, [mx, sortedLowPriorityRooms, filterQuery]);
+
   const sortedRooms = useMemo(() => {
     const isClosed = closedCategories.has(DEFAULT_CATEGORY_ID);
     let comparator: (a: string, b: string) => number;
@@ -349,6 +375,13 @@ export function Home() {
     overscan: 10,
   });
 
+  const lowVirtualizer = useVirtualizer({
+    count: filteredLowPriorityRooms.length,
+    getScrollElement: () => scrollRef.current,
+    estimateSize: () => 38,
+    overscan: 10,
+  });
+
   const handleCategoryClick = useCategoryHandler(setClosedCategories, (categoryId) =>
     closedCategories.has(categoryId),
   );
@@ -638,6 +671,43 @@ export function Home() {
                 })}
               </div>
             </NavCategory>
+            {lowPriorityRooms.length > 0 && (
+              <NavCategory>
+                <NavCategoryHeader>
+                  <RoomNavCategoryButton
+                    closed={closedCategories.has(LOW_PRIORITY_CATEGORY_ID)}
+                    data-category-id={LOW_PRIORITY_CATEGORY_ID}
+                    onClick={handleCategoryClick}
+                  >
+                    Low Priority
+                  </RoomNavCategoryButton>
+                </NavCategoryHeader>
+                <div style={{ position: 'relative', height: lowVirtualizer.getTotalSize() }}>
+                  {lowVirtualizer.getVirtualItems().map((vItem) => {
+                    const roomId = filteredLowPriorityRooms[vItem.index];
+                    const room = mx.getRoom(roomId);
+                    if (!room) return null;
+                    return (
+                      <VirtualTile
+                        virtualItem={vItem}
+                        key={roomId}
+                        ref={lowVirtualizer.measureElement}
+                      >
+                        <RoomNavItem
+                          room={room}
+                          selected={selectedRoomId === roomId}
+                          linkPath={getHomeRoomPath(getCanonicalAliasOrRoomId(mx, roomId))}
+                          notificationMode={getRoomNotificationMode(
+                            notificationPreferences,
+                            room.roomId,
+                          )}
+                        />
+                      </VirtualTile>
+                    );
+                  })}
+                </div>
+              </NavCategory>
+            )}
           </Box>
         </PageNavContent>
       )}

src/app/state/hooks/useBindAtoms.ts

@@ -3,6 +3,7 @@ import { allInvitesAtom, useBindAllInvitesAtom } from '../room-list/inviteList';
 import { allRoomsAtom, useBindAllRoomsAtom } from '../room-list/roomList';
 import { mDirectAtom, useBindMDirectAtom } from '../mDirectList';
 import { roomToUnreadAtom, useBindRoomToUnreadAtom } from '../room/roomToUnread';
+import { markedUnreadAtom, useBindMarkedUnreadAtom } from '../room/markedUnread';
 import { roomToParentsAtom, useBindRoomToParentsAtom } from '../room/roomToParents';
 import { roomIdToTypingMembersAtom, useBindRoomIdToTypingMembersAtom } from '../typingMembers';
 import { threadNotificationsAtom, useBindThreadNotificationsAtom } from '../threadNotifications';
@@ -14,6 +15,7 @@ export const useBindAtoms = (mx: MatrixClient) => {
   useBindRoomToParentsAtom(mx, roomToParentsAtom);
   useBindThreadNotificationsAtom(mx, threadNotificationsAtom);
   useBindRoomToUnreadAtom(mx, roomToUnreadAtom);
+  useBindMarkedUnreadAtom(mx, markedUnreadAtom);
 
   useBindRoomIdToTypingMembersAtom(mx, roomIdToTypingMembersAtom);
 };

src/app/state/room/markedUnread.test.ts

@@ -0,0 +1,65 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { MatrixEvent } from 'matrix-js-sdk';
+import { receiptIsMine, setMarkedUnread } from './markedUnread';
+
+// MSC2867 mark-as-unread: reading a room (our own receipt) clears the flag, so
+// `receiptIsMine` must detect only OUR receipt and ignore others'. And a write
+// must land on BOTH the stable `m.marked_unread` and the unstable
+// `com.famedly.marked_unread` key so it round-trips across servers/clients.
+
+const ME = '@me:server';
+const OTHER = '@friend:server';
+
+const receiptEvent = (content: object): MatrixEvent =>
+  ({ getContent: () => content }) as MatrixEvent;
+
+test('receiptIsMine: true when the receipt content carries our user id', () => {
+  const event = receiptEvent({
+    $abc: { 'm.read': { [ME]: { ts: 1 } } },
+  });
+  assert.equal(receiptIsMine(event, ME), true);
+});
+
+test('receiptIsMine: false when only another user has a receipt', () => {
+  const event = receiptEvent({
+    $abc: { 'm.read': { [OTHER]: { ts: 1 } } },
+  });
+  assert.equal(receiptIsMine(event, ME), false);
+});
+
+test('receiptIsMine: tolerates empty / malformed content', () => {
+  assert.equal(receiptIsMine(receiptEvent({}), ME), false);
+  assert.equal(receiptIsMine(receiptEvent({ $x: {} }), ME), false);
+});
+
+test('setMarkedUnread writes both the stable and unstable keys with the flag', async () => {
+  const calls: Array<{ type: string; content: unknown }> = [];
+  const mx = {
+    setRoomAccountData: (_roomId: string, type: string, content: unknown) => {
+      calls.push({ type, content });
+      return Promise.resolve();
+    },
+  } as any;
+
+  await setMarkedUnread(mx, '!room:server', true);
+
+  const types = calls.map((c) => c.type).sort();
+  assert.deepEqual(types, ['com.famedly.marked_unread', 'm.marked_unread']);
+  assert.ok(calls.every((c) => (c.content as { unread: boolean }).unread === true));
+});
+
+test('setMarkedUnread(false) clears both keys and does not reject if the unstable write fails', async () => {
+  const seen: string[] = [];
+  const mx = {
+    setRoomAccountData: (_roomId: string, type: string) => {
+      seen.push(type);
+      // Simulate an older server rejecting the unstable key — must not reject.
+      if (type === 'com.famedly.marked_unread') return Promise.reject(new Error('unknown type'));
+      return Promise.resolve();
+    },
+  } as any;
+
+  await assert.doesNotReject(() => setMarkedUnread(mx, '!room:server', false));
+  assert.ok(seen.includes('m.marked_unread'));
+});

src/app/state/room/markedUnread.ts

@@ -0,0 +1,97 @@
+import { atom, useSetAtom } from 'jotai';
+import { MatrixClient, MatrixEvent, Room, RoomEvent, RoomEventHandlerMap } from 'matrix-js-sdk';
+import { useEffect } from 'react';
+import { AccountDataEvent } from '../../../types/matrix/accountData';
+
+// MSC2867 — "mark a room as unread". A per-room account-data flag `{ unread }`.
+// Stable type `m.marked_unread`; servers/clients predating the stabilization use
+// the unstable `com.famedly.marked_unread`. We read either and write both so the
+// flag round-trips across the ecosystem.
+const UNSTABLE_MARKED_UNREAD = 'com.famedly.marked_unread';
+
+const readMarkedUnread = (room: Room): boolean => {
+  const stable = room.getAccountData(AccountDataEvent.MarkedUnread)?.getContent()?.unread;
+  if (typeof stable === 'boolean') return stable;
+  return room.getAccountData(UNSTABLE_MARKED_UNREAD)?.getContent()?.unread === true;
+};
+
+/** Set of room ids the user has explicitly marked as unread. */
+export const markedUnreadAtom = atom<Set<string>>(new Set<string>());
+
+/** Write (or clear) the marked-unread flag on both the stable + unstable keys. */
+export const setMarkedUnread = (
+  mx: MatrixClient,
+  roomId: string,
+  unread: boolean,
+): Promise<unknown> =>
+  Promise.all([
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    mx.setRoomAccountData(roomId, AccountDataEvent.MarkedUnread as any, { unread }),
+    // Best-effort mirror for older servers; never fail the primary write on it.
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    mx.setRoomAccountData(roomId, UNSTABLE_MARKED_UNREAD as any, { unread }).catch(() => undefined),
+  ]);
+
+export const receiptIsMine = (event: MatrixEvent, userId: string): boolean => {
+  const content = event.getContent();
+  return Object.keys(content).some((eventId) =>
+    Object.keys(content[eventId] ?? {}).some(
+      (receiptType) => content[eventId][receiptType]?.[userId],
+    ),
+  );
+};
+
+export const useBindMarkedUnreadAtom = (mx: MatrixClient, anAtom: typeof markedUnreadAtom) => {
+  const setAtom = useSetAtom(anAtom);
+
+  useEffect(() => {
+    const seed = new Set<string>();
+    mx.getRooms().forEach((room) => {
+      if (readMarkedUnread(room)) seed.add(room.roomId);
+    });
+    setAtom(seed);
+
+    const syncRoom = (room: Room) => {
+      const marked = readMarkedUnread(room);
+      setAtom((prev) => {
+        if (marked === prev.has(room.roomId)) return prev;
+        const next = new Set(prev);
+        if (marked) next.add(room.roomId);
+        else next.delete(room.roomId);
+        return next;
+      });
+    };
+
+    const onAccountData: RoomEventHandlerMap[RoomEvent.AccountData] = (_event, room) => {
+      syncRoom(room);
+    };
+    // Reading a room clears its marked-unread flag (MSC2867): when our own read
+    // receipt lands for a room that's currently marked, clear it.
+    const onReceipt: RoomEventHandlerMap[RoomEvent.Receipt] = (event, room) => {
+      const myId = mx.getUserId();
+      if (!myId || !readMarkedUnread(room)) return;
+      if (receiptIsMine(event, myId)) {
+        setMarkedUnread(mx, room.roomId, false).catch(() => undefined);
+      }
+    };
+    const onMembership: RoomEventHandlerMap[RoomEvent.MyMembership] = (room) => {
+      if (room.getMyMembership() !== 'join') {
+        setAtom((prev) => {
+          if (!prev.has(room.roomId)) return prev;
+          const next = new Set(prev);
+          next.delete(room.roomId);
+          return next;
+        });
+      }
+    };
+
+    mx.on(RoomEvent.AccountData, onAccountData);
+    mx.on(RoomEvent.Receipt, onReceipt);
+    mx.on(RoomEvent.MyMembership, onMembership);
+    return () => {
+      mx.removeListener(RoomEvent.AccountData, onAccountData);
+      mx.removeListener(RoomEvent.Receipt, onReceipt);
+      mx.removeListener(RoomEvent.MyMembership, onMembership);
+    };
+  }, [mx, setAtom]);
+};

src/app/state/settings.ts

@@ -183,6 +183,9 @@ export interface Settings {
   urlPreview: boolean;
   encUrlPreview: boolean;
   showHiddenEvents: boolean;
+  // [MSC1763] Opt-in: permanently redact your OWN messages once a room's
+  // retention window passes (default off — nothing auto-deletes by surprise).
+  enforceRetentionLocally: boolean;
   legacyUsernameColor: boolean;
 
   showNotifications: boolean;
@@ -288,6 +291,7 @@ const defaultSettings: Settings = {
   urlPreview: true,
   encUrlPreview: true,
   showHiddenEvents: false,
+  enforceRetentionLocally: false,
   legacyUsernameColor: false,
 
   showNotifications: true,

src/app/utils/retention.test.ts

@@ -0,0 +1,42 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { isExpired, RETENTION_PRESETS, RETENTION_MIN_MS } from './retention';
+
+// MSC1763 retention: `isExpired` decides whether a message is past the room's
+// retention window. It must be strict (> window, not >=) and a disabled policy
+// (0) must never expire anything.
+
+const HOUR = 60 * 60 * 1000;
+
+test('isExpired: an event older than the window is expired', () => {
+  const now = 10 * HOUR;
+  assert.equal(isExpired(now - 2 * HOUR, HOUR, now), true);
+});
+
+test('isExpired: an event within the window is NOT expired', () => {
+  const now = 10 * HOUR;
+  assert.equal(isExpired(now - HOUR / 2, HOUR, now), false);
+});
+
+test('isExpired: exactly at the boundary is NOT expired (strict >)', () => {
+  const now = 10 * HOUR;
+  assert.equal(isExpired(now - HOUR, HOUR, now), false);
+});
+
+test('isExpired: a disabled policy (0 / negative) never expires', () => {
+  const now = 10 * HOUR;
+  assert.equal(isExpired(now - 100 * HOUR, 0, now), false);
+  assert.equal(isExpired(0, -1, now), false);
+});
+
+test('presets: Off is 0 and the rest are strictly increasing, all >= the floor', () => {
+  assert.equal(RETENTION_PRESETS[0].ms, 0);
+  const nonZero = RETENTION_PRESETS.slice(1).map((p) => p.ms);
+  for (let i = 1; i < nonZero.length; i += 1) {
+    assert.ok(nonZero[i] > nonZero[i - 1], 'presets increase');
+  }
+  assert.ok(
+    nonZero.every((ms) => ms >= RETENTION_MIN_MS),
+    'all presets above the floor',
+  );
+});

src/app/utils/retention.ts

@@ -0,0 +1,32 @@
+import { Room } from 'matrix-js-sdk';
+import { StateEvent } from '../../types/matrix/room';
+
+// MSC1763 — per-room message retention (`m.room.retention`). `max_lifetime` is a
+// duration in milliseconds after which a message is considered expired.
+export type RetentionContent = {
+  max_lifetime?: number;
+};
+
+const DAY_MS = 24 * 60 * 60 * 1000;
+
+// Floor to avoid foot-guns (an admin fat-fingering a tiny value nuking a room).
+export const RETENTION_MIN_MS = 10 * 60 * 1000;
+
+export type RetentionPreset = { label: string; ms: number };
+export const RETENTION_PRESETS: RetentionPreset[] = [
+  { label: 'Off', ms: 0 },
+  { label: '1 Day', ms: DAY_MS },
+  { label: '1 Week', ms: 7 * DAY_MS },
+  { label: '1 Month', ms: 30 * DAY_MS },
+];
+
+/** The room's active retention window in ms, or `undefined` when unset/disabled. */
+export const getRoomRetentionMs = (room: Room): number | undefined => {
+  const event = room.currentState.getStateEvents(StateEvent.RoomRetention, '');
+  const ms = event?.getContent<RetentionContent>()?.max_lifetime;
+  return typeof ms === 'number' && ms > 0 ? ms : undefined;
+};
+
+/** True when an event at `tsMs` has passed the `maxLifetimeMs` retention window. */
+export const isExpired = (tsMs: number, maxLifetimeMs: number, nowMs: number): boolean =>
+  maxLifetimeMs > 0 && nowMs - tsMs > maxLifetimeMs;

src/client/initMatrix.ts

@@ -38,7 +38,8 @@ export const initClient = async (session: Session): Promise<MatrixClient> => {
     deviceId: session.deviceId,
     timelineSupport: true,
     cryptoCallbacks: cryptoCallbacks as any,
-    verificationMethods: ['m.sas.v1'],
+    // SAS (emoji) + QR-code verification (show/scan/reciprocate).
+    verificationMethods: ['m.sas.v1', 'm.qr_code.show.v1', 'm.qr_code.scan.v1', 'm.reciprocate.v1'],
     tokenRefreshFunction: oidcRefresher
       ? (refreshToken) => oidcRefresher.doRefreshAccessToken(refreshToken)
       : undefined,

src/types/matrix/accountData.ts

@@ -2,6 +2,8 @@ export enum AccountDataEvent {
   PushRules = 'm.push_rules',
   Direct = 'm.direct',
   IgnoredUserList = 'm.ignored_user_list',
+  // [MSC2867] Per-room "mark as unread" flag (room account data).
+  MarkedUnread = 'm.marked_unread',
 
   CinnySpaces = 'in.cinny.spaces',
 

src/types/matrix/room.ts

@@ -29,6 +29,8 @@ export enum StateEvent {
   RoomPinnedEvents = 'm.room.pinned_events',
   RoomEncryption = 'm.room.encryption',
   RoomHistoryVisibility = 'm.room.history_visibility',
+  // [MSC1763] Per-room message retention policy (disappearing messages).
+  RoomRetention = 'm.room.retention',
   RoomGuestAccess = 'm.room.guest_access',
   RoomServerAcl = 'm.room.server_acl',
   RoomTombstone = 'm.room.tombstone',