fix(retention): a tiny or brand-new retention value can't wipe a room (#298)

m.room.retention can be set to anything by anyone with state power. A
fat-fingered `max_lifetime: 1000` blanked the timeline for every Lotus
user and, for members with "Enforce Message Retention" on, the sweeper
redacted all their messages within a minute. The RETENTION_MIN_MS floor
existed but was never applied.

- effectiveRetentionMs(): anything under 10 min counts as off; used by
  getRoomRetentionMs (sweeper) and the timeline's hiding.
- The sweeper never deletes under a policy less than 24 h old, so a
  mistake or a malicious change can be reverted before anything is lost.
  (Local hiding of expired messages still applies at once.)

Verified headless (the issue's repro, enforcement on): after
max_lifetime 1000, all 4 messages stay visible and none are redacted
after 45 s (before: timeline blank, all 4 redacted). Unit tests for the
floor and the grace window.

Fixes #298

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/components/CallEmbedProvider.tsx

@@ -20,7 +20,6 @@ import {
 import {
   EventTimelineSetHandlerMap,
   EventType,
-  JoinRule,
   RelationType,
   Room,
   RoomEvent,
@@ -72,7 +71,8 @@ import { useReducedMotion } from '../hooks/useReducedMotion';
 import { useSetting } from '../state/hooks/settings';
 import { useCallPreferences } from '../state/hooks/callPreferences';
 import { settingsAtom } from '../state/settings';
-import { getStateEvent, getStateEvents, getMemberName } from '../utils/room';
+import { getStateEvent, getMemberName } from '../utils/room';
+import { isRingableRoom } from '../utils/callRing';
 import { StateEvent } from '../../types/matrix/room';
 import { getPowersLevelFromMatrixEvent } from '../hooks/usePowerLevels';
 import { getRoomCreatorsForRoomId } from '../hooks/useRoomCreators';
@@ -581,12 +581,7 @@ function IncomingCallListener({ callEmbed, joined }: IncomingCallListenerProps)
       // Only ring in rooms where the call button is visible: DMs or invite-only rooms
       // with no space parent. Persistent voice rooms (call rooms), space channels,
       // restricted rooms, and public rooms must never trigger ringing.
-      if (room.isCallRoom()) return;
-      const isDirect = directs.has(room.roomId);
-      const isSpaceChild = getStateEvents(room, StateEvent.SpaceParent).length > 0;
-      const joinRule = room.getJoinRule();
-      const isPrivateInviteGroup = !isSpaceChild && joinRule === JoinRule.Invite;
-      if (!isDirect && !isPrivateInviteGroup) return;
+      if (!isRingableRoom(room, directs.has(room.roomId))) return;
 
       const info: IncomingCallInfo = {
         room,

src/app/features/lotus/backgrounds/animAurora.ts

@@ -51,7 +51,7 @@ const dark: CSSProperties = {
   backgroundSize: '260% 240%, 300% 260%, 240% 280%, 220% 200%, 100% 100%, 100% 100%',
   backgroundPosition: '0% 30%, 100% 70%, 50% 0%, 20% 80%, 50% 50%, 50% 50%',
   backgroundRepeat: 'no-repeat',
-  animation: `${auroraFlow} 60s ease-in-out infinite`,
+  animation: `${auroraFlow} 60s steps(180) infinite`,
 };
 
 const light: CSSProperties = {
@@ -75,7 +75,7 @@ const light: CSSProperties = {
   backgroundSize: '260% 240%, 300% 260%, 240% 280%, 220% 200%, 100% 100%, 100% 100%',
   backgroundPosition: '0% 30%, 100% 70%, 50% 0%, 20% 80%, 50% 50%, 50% 50%',
   backgroundRepeat: 'no-repeat',
-  animation: `${auroraFlow} 60s ease-in-out infinite`,
+  animation: `${auroraFlow} 60s steps(180) infinite`,
 };
 
 export const animAurora: ChatBgVariants = { dark, light };

src/app/features/lotus/backgrounds/animFireflies.ts

@@ -55,7 +55,7 @@ export const animFireflies: ChatBgVariants = {
       '0 0', // wash A   (static)
       '0 0', // wash B   (static)
     ].join(','),
-    animation: `${firefliesDrift} 44s linear infinite`,
+    animation: `${firefliesDrift} 44s steps(528) infinite`,
   },
 
   // Light: a cozy warm dim-dusk. No harsh dots on white — soft amber motes with
@@ -93,6 +93,6 @@ export const animFireflies: ChatBgVariants = {
       '0 0', // wash A   (static)
       '0 0', // wash B   (static)
     ].join(','),
-    animation: `${firefliesDrift} 44s linear infinite`,
+    animation: `${firefliesDrift} 44s steps(528) infinite`,
   },
 };

src/app/features/lotus/backgrounds/animPulse.ts

@@ -76,7 +76,7 @@ export const animPulse: ChatBgVariants = {
       '0 0', // base wash
       '0 0', // vignette
     ].join(','),
-    animation: `${gridPulse} 22s ease-in-out infinite`,
+    animation: `${gridPulse} 22s steps(528) infinite`,
   },
 
   // Light: soft slate-blue grid on pale cool-white, a gentle luminance breathe.
@@ -116,6 +116,6 @@ export const animPulse: ChatBgVariants = {
       '0 0', // base wash
       '0 0', // vignette
     ].join(','),
-    animation: `${gridPulse} 22s ease-in-out infinite`,
+    animation: `${gridPulse} 22s steps(528) infinite`,
   },
 };

src/app/features/lotus/backgrounds/animRain.ts

@@ -97,7 +97,7 @@ export const animRain: ChatBgVariants = {
     ].join(','),
     backgroundSize: ['260px 200px', '100% 100%', '100% 100%', '100% 100%'].join(','),
     backgroundPosition: ['0 0', '0 0', '0 0', '0 0'].join(','),
-    animation: `${rainFall} 12s linear infinite`,
+    animation: `${rainFall} 12s steps(288) infinite`,
   },
 
   // Light: soft teal-grey streaks on a pale cool base — elegant, never neon.
@@ -118,6 +118,6 @@ export const animRain: ChatBgVariants = {
     ].join(','),
     backgroundSize: ['260px 200px', '100% 100%', '100% 100%', '100% 100%'].join(','),
     backgroundPosition: ['0 0', '0 0', '0 0', '0 0'].join(','),
-    animation: `${rainFall} 12s linear infinite`,
+    animation: `${rainFall} 12s steps(288) infinite`,
   },
 };

src/app/features/lotus/backgrounds/animStars.ts

@@ -68,7 +68,7 @@ export const animStars: ChatBgVariants = {
       '0 0', // nebula A
       '0 0', // nebula B
     ].join(','),
-    animation: `${starDrift} 90s linear infinite`,
+    animation: `${starDrift} 90s steps(1080) infinite`,
   },
 
   // Light: an airy pre-dawn sky. No literal white-on-white stars — instead very
@@ -112,6 +112,6 @@ export const animStars: ChatBgVariants = {
       '0 0', // wash A
       '0 0', // wash B
     ].join(','),
-    animation: `${starDrift} 100s linear infinite`,
+    animation: `${starDrift} 100s steps(1200) infinite`,
   },
 };

src/app/features/lotus/chatBackground.ts

@@ -149,6 +149,11 @@ export const getChatBg = (
   }
   // For animated backgrounds, promote the element to its own compositor layer so
   // background-position keyframes don't trigger repaints on descendant elements.
+  // [Gitea #337] background-position can't run on the compositor, so every
+  // animation frame repaints the whole chat area (45 to 70% main-thread busy
+  // at 60 fps). The drifts are slow (3–22 px/s), so each animation uses steps():
+  // ~12 updates/s for the slow ones, ~24/s for rain and pulse: visually the
+  // same, a fraction of the repaints.
   if (style.animation) {
     return { ...style, willChange: 'background-position', contain: 'paint' };
   }

src/app/features/room/RoomTimeline.tsx

@@ -121,7 +121,7 @@ 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 { RetentionContent, effectiveRetentionMs, isExpired } from '../../utils/retention';
 import { useKeyDown } from '../../hooks/useKeyDown';
 import { useDocumentFocusChange } from '../../hooks/useDocumentFocusChange';
 import { RenderMessageContent } from '../../components/RenderMessageContent';
@@ -138,6 +138,7 @@ import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
 import { useIgnoredUsers } from '../../hooks/useIgnoredUsers';
 import { useImagePackRooms } from '../../hooks/useImagePackRooms';
 import { useIsDirectRoom } from '../../hooks/useRoom';
+import { isRingableRoom } from '../../utils/callRing';
 import { useOpenUserRoomProfile } from '../../state/hooks/userRoomProfile';
 import { useSpaceOptionally } from '../../hooks/useSpace';
 import { useRoomCreators } from '../../hooks/useRoomCreators';
@@ -493,7 +494,10 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
   // 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;
+  // [Gitea #298] Same floor as everywhere else: a tiny value must not blank the room.
+  const retentionMs = effectiveRetentionMs(
+    retentionEvent?.getContent<RetentionContent>().max_lifetime,
+  );
   const [showDeveloperTools] = useSetting(settingsAtom, 'developerTools');
   const [lotusTerminal] = useSetting(settingsAtom, 'lotusTerminal');
 
@@ -2030,6 +2034,9 @@ export function RoomTimeline({ room, eventId, roomInputRef, editor }: RoomTimeli
       [EventType.RTCNotification]: (mEventId, mEvent, item) => {
         const senderId = mEvent.getSender() ?? '';
         if (!senderId || senderId === mx.getUserId()) return null;
+        // Same rule as ringing: no "Missed call" in voice rooms or space
+        // channels, where starting a call is just joining the channel.
+        if (!isRingableRoom(room, direct)) return null;
         const content = mEvent.getContent();
         const mention =
           content['m.mentions']?.room ||

src/app/pages/client/ClientNonUIFeatures.tsx

@@ -68,7 +68,12 @@ import { setPresenceWithRetry } from '../../utils/presenceWrite';
 import { useDeepLinkNavigate } from '../../hooks/useDeepLinkNavigate';
 import { dismissToastAtom, toastQueueAtom } from '../../state/toast';
 import { useReminders } from '../../hooks/useReminders';
-import { getRoomRetentionMs, isExpired } from '../../utils/retention';
+import {
+  getRoomRetentionMs,
+  getRoomRetentionSetAt,
+  isExpired,
+  retentionDeletesAllowed,
+} from '../../utils/retention';
 import { useTauriUpdateProgress, useTauriUpdater } from '../../hooks/useTauriUpdater';
 import { settingsRequestAtom } from '../../state/settingsRequest';
 import { isNetworkUpdateError } from '../../utils/updateErrors';
@@ -910,6 +915,9 @@ function RetentionSweeper() {
       mx.getRooms().forEach((room) => {
         const maxLifetime = getRoomRetentionMs(room);
         if (!maxLifetime) return;
+        // [Gitea #298] Never delete under a policy that is less than a day old.
+        const setAt = getRoomRetentionSetAt(room);
+        if (setAt === undefined || !retentionDeletesAllowed(setAt, now)) return;
         room
           .getLiveTimeline()
           .getEvents()

src/app/utils/callRing.test.ts

@@ -0,0 +1,29 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import type { Room } from 'matrix-js-sdk';
+import { isRingableRoom } from './callRing';
+
+const fakeRoom = (opts: { callRoom?: boolean; joinRule?: string; spaceParent?: boolean }): Room =>
+  ({
+    isCallRoom: () => !!opts.callRoom,
+    getJoinRule: () => opts.joinRule ?? 'invite',
+    getLiveTimeline: () => ({
+      getState: () => ({ getStateEvents: () => (opts.spaceParent ? [{}] : []) }),
+    }),
+  }) as unknown as Room;
+
+test('voice rooms never ring or show "missed call", even as DMs', () => {
+  assert.equal(isRingableRoom(fakeRoom({ callRoom: true }), false), false);
+  assert.equal(isRingableRoom(fakeRoom({ callRoom: true }), true), false);
+});
+
+test('DMs and invite-only groups outside a space ring', () => {
+  assert.equal(isRingableRoom(fakeRoom({ joinRule: 'public' }), true), true);
+  assert.equal(isRingableRoom(fakeRoom({ joinRule: 'invite' }), false), true);
+});
+
+test('space channels, public and restricted rooms do not ring', () => {
+  assert.equal(isRingableRoom(fakeRoom({ joinRule: 'invite', spaceParent: true }), false), false);
+  assert.equal(isRingableRoom(fakeRoom({ joinRule: 'public' }), false), false);
+  assert.equal(isRingableRoom(fakeRoom({ joinRule: 'restricted' }), false), false);
+});

src/app/utils/callRing.ts

@@ -0,0 +1,18 @@
+import { JoinRule, Room } from 'matrix-js-sdk';
+import { StateEvent } from '../../types/matrix/room';
+import { getStateEvents } from './room';
+
+/**
+ * Whether a call notification in this room may ring — and, by the same rule,
+ * whether an unanswered one may show as "Missed call" (Gitea #162 follow-up).
+ * Only DMs and invite-only groups outside any space ring, i.e. rooms where the
+ * call button is shown. Persistent voice rooms, space channels, restricted and
+ * public rooms never do: joining a voice channel alone is normal and isn't a
+ * "call" anyone missed.
+ */
+export const isRingableRoom = (room: Room, isDirect: boolean): boolean => {
+  if (room.isCallRoom()) return false;
+  if (isDirect) return true;
+  const isSpaceChild = getStateEvents(room, StateEvent.SpaceParent).length > 0;
+  return !isSpaceChild && room.getJoinRule() === JoinRule.Invite;
+};

src/app/utils/linkSafety.test.ts

@@ -38,3 +38,38 @@ test('hostFromText only accepts URL/host-shaped text; IDN becomes punycode', ()
   assert.equal(analyzeLink('paypal.com', 'https://xn--pypal-4ve.com/')?.punycode, true);
   assert.equal(analyzeLink('paypal.com', 'https://xn--pypal-4ve.com/')?.mismatch, true);
 });
+
+test('a trusted name inside a sentence still exposes a different destination (#335)', () => {
+  const a = analyzeLink('Log in at chat.lotusguild.org', 'https://evil.example/');
+  assert.equal(a?.mismatch, true);
+  assert.equal(a?.shownHost, 'chat.lotusguild.org');
+  assert.equal(
+    analyzeLink('chat.lotusguild.org (official)', 'https://evil.example/')?.mismatch,
+    true,
+  );
+  assert.equal(
+    analyzeLink('Open https://paypal.com/login now', 'https://evil.example/')?.mismatch,
+    true,
+  );
+  // honest sentences are not flagged
+  assert.equal(
+    analyzeLink('Log in at chat.lotusguild.org', 'https://chat.lotusguild.org/login')?.mismatch,
+    false,
+  );
+  assert.equal(analyzeLink('read the docs', 'https://evil.example/')?.mismatch, false);
+  assert.equal(analyzeLink('see main.py and report.pdf', 'https://github.com/x')?.mismatch, false);
+  assert.equal(analyzeLink('release v1.2.3 notes', 'https://github.com/x')?.mismatch, false);
+});
+
+test('shared hosting suffixes are separate sites (#335)', () => {
+  assert.equal(registrableDomain('alice.github.io'), 'alice.github.io');
+  assert.equal(registrableDomain('www.alice.github.io'), 'alice.github.io');
+  assert.equal(registrableDomain('bucket.s3.amazonaws.com'), 'bucket.s3.amazonaws.com');
+  assert.equal(analyzeLink('alice.github.io', 'https://evil.github.io/')?.mismatch, true);
+  assert.equal(analyzeLink('lotusguild.pages.dev', 'https://evil.pages.dev/')?.mismatch, true);
+  assert.equal(
+    analyzeLink('alice.github.io/blog', 'https://alice.github.io/blog/1')?.mismatch,
+    false,
+  );
+  assert.equal(registrableDomain('news.bbc.co.uk'), 'bbc.co.uk');
+});

src/app/utils/linkSafety.ts

@@ -48,11 +48,53 @@ const TWO_LABEL_SUFFIXES = new Set([
   'com.tw',
 ]);
 
+// [Gitea #335] Shared-hosting suffixes (the Public Suffix List's "private"
+// section, the ones phishing actually uses): every customer gets their own
+// subdomain, so `alice.github.io` and `evil.github.io` are different sites.
+// A curated list rather than the full PSL keeps this out of the bundle budget.
+const SHARED_HOSTING_SUFFIXES = new Set([
+  'github.io',
+  'gitlab.io',
+  'codeberg.page',
+  'pages.dev',
+  'workers.dev',
+  'trycloudflare.com',
+  'netlify.app',
+  'vercel.app',
+  'web.app',
+  'firebaseapp.com',
+  'appspot.com',
+  'herokuapp.com',
+  'onrender.com',
+  'fly.dev',
+  'glitch.me',
+  'replit.app',
+  'repl.co',
+  'surge.sh',
+  'blogspot.com',
+  'wordpress.com',
+  'wixsite.com',
+  'weebly.com',
+  'azurewebsites.net',
+  'cloudfront.net',
+  'ngrok.io',
+  'ngrok-free.app',
+  'duckdns.org',
+  's3.amazonaws.com',
+]);
+
+const isPublicSuffix = (suffix: string): boolean =>
+  TWO_LABEL_SUFFIXES.has(suffix) || SHARED_HOSTING_SUFFIXES.has(suffix);
+
 export const registrableDomain = (host: string): string => {
   const labels = host.toLowerCase().replace(/\.$/, '').split('.');
-  if (labels.length <= 2) return labels.join('.');
-  const lastTwo = labels.slice(-2).join('.');
-  return TWO_LABEL_SUFFIXES.has(lastTwo) ? labels.slice(-3).join('.') : lastTwo;
+  // Longest matching public suffix wins (3 labels, e.g. s3.amazonaws.com, then 2).
+  for (const n of [3, 2]) {
+    if (labels.length > n && isPublicSuffix(labels.slice(-n).join('.'))) {
+      return labels.slice(-(n + 1)).join('.');
+    }
+  }
+  return labels.slice(-2).join('.');
 };
 
 const HOST_LIKE =
@@ -72,6 +114,85 @@ export const hostFromText = (text: string): string | null => {
   }
 };
 
+// Words that look like hosts but are usually files or versions in chat
+// ("see main.py", "report.pdf", "v1.2.3"): skipped inside sentences unless
+// written as a URL (scheme, www., or a path) so ordinary links aren't flagged.
+const FILE_EXTENSIONS = new Set([
+  'py',
+  'sh',
+  'md',
+  'rs',
+  'js',
+  'ts',
+  'tsx',
+  'jsx',
+  'json',
+  'yaml',
+  'yml',
+  'toml',
+  'txt',
+  'log',
+  'csv',
+  'pdf',
+  'zip',
+  'gz',
+  'tar',
+  'png',
+  'jpg',
+  'jpeg',
+  'gif',
+  'webp',
+  'svg',
+  'mp3',
+  'mp4',
+  'mov',
+  'html',
+  'htm',
+  'css',
+  'exe',
+  'dll',
+  'lock',
+  'cfg',
+  'conf',
+  'ini',
+  'xml',
+  'doc',
+  'docx',
+  'xls',
+  'xlsx',
+  'ppt',
+  'pptx',
+  'apk',
+  'iso',
+  'jar',
+  'java',
+  'go',
+  'rb',
+  'php',
+  'c',
+  'h',
+  'cpp',
+]);
+const TRIM_PUNCT = /^[\s"'“”‘’«»([{<]+|[\s"'“”‘’«»)\]}>.,;:!?]+$/g;
+
+/** Every host a sentence names (Gitea #335), e.g. "Log in at chat.lotusguild.org". */
+export const hostsFromText = (text: string): string[] => {
+  const hosts: string[] = [];
+  text.split(/\s+/).forEach((raw) => {
+    const word = raw.replace(TRIM_PUNCT, '');
+    const host = word && hostFromText(word);
+    if (!host) return;
+    const tld = host.split('.').pop() ?? '';
+    if (!/[a-z]/i.test(tld)) return; // version numbers, IPs-as-words
+    const urlShaped =
+      /^[a-z][a-z0-9+.-]*:\/\//i.test(word) || /^www\./i.test(word) || word.includes('/');
+    if (!urlShaped && host.split('.').length === 2 && FILE_EXTENSIONS.has(tld.toLowerCase()))
+      return;
+    if (!hosts.includes(host)) hosts.push(host);
+  });
+  return hosts;
+};
+
 export type LinkSafety = {
   /** The visible text names a different site than the destination. */
   mismatch: boolean;
@@ -92,8 +213,11 @@ export const analyzeLink = (text: string, href: string): LinkSafety | null => {
   if (url.hostname === 'matrix.to') return null;
   const realHost = url.hostname;
   const punycode = realHost.split('.').some((l) => l.startsWith('xn--'));
-  const shownHost = hostFromText(text) ?? undefined;
-  const mismatch =
-    shownHost !== undefined && registrableDomain(shownHost) !== registrableDomain(realHost);
-  return { mismatch, shownHost, realHost, punycode };
+  // A single URL/host-shaped text, or (Gitea #335) host-shaped words inside a
+  // sentence: "Log in at chat.lotusguild.org" must not hide a different site.
+  const single = hostFromText(text);
+  const shown = single ? [single] : hostsFromText(text);
+  const realSite = registrableDomain(realHost);
+  const other = shown.find((h) => registrableDomain(h) !== realSite);
+  return { mismatch: other !== undefined, shownHost: other ?? shown[0], realHost, punycode };
 };

src/app/utils/retention.test.ts

@@ -1,6 +1,13 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
-import { isExpired, RETENTION_PRESETS, RETENTION_MIN_MS } from './retention';
+import {
+  effectiveRetentionMs,
+  isExpired,
+  RETENTION_DELETE_GRACE_MS,
+  RETENTION_MIN_MS,
+  RETENTION_PRESETS,
+  retentionDeletesAllowed,
+} 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
@@ -40,3 +47,22 @@ test('presets: Off is 0 and the rest are strictly increasing, all >= the floor',
     'all presets above the floor',
   );
 });
+
+test('effectiveRetentionMs: tiny or invalid windows count as off (#298)', () => {
+  assert.equal(effectiveRetentionMs(1000), undefined, '1 s is a typo, not a policy');
+  assert.equal(effectiveRetentionMs(RETENTION_MIN_MS - 1), undefined);
+  assert.equal(effectiveRetentionMs(RETENTION_MIN_MS), RETENTION_MIN_MS);
+  assert.equal(effectiveRetentionMs(86_400_000), 86_400_000);
+  assert.equal(effectiveRetentionMs(0), undefined);
+  assert.equal(effectiveRetentionMs(-5), undefined);
+  assert.equal(effectiveRetentionMs('86400000'), undefined);
+  assert.equal(effectiveRetentionMs(Number.NaN), undefined);
+});
+
+test('retentionDeletesAllowed: no deletions in the first 24 h of a policy (#298)', () => {
+  const now = 1_000 * HOUR;
+  assert.equal(retentionDeletesAllowed(now - 2 * HOUR, now), false);
+  assert.equal(retentionDeletesAllowed(now - RETENTION_DELETE_GRACE_MS + 1, now), false);
+  assert.equal(retentionDeletesAllowed(now - RETENTION_DELETE_GRACE_MS, now), true);
+  assert.equal(retentionDeletesAllowed(now - 72 * HOUR, now), true);
+});

src/app/utils/retention.ts

@@ -20,13 +20,38 @@ export const RETENTION_PRESETS: RetentionPreset[] = [
   { label: '1 Month', ms: 30 * DAY_MS },
 ];
 
+/**
+ * [Gitea #298] A usable retention window, or `undefined`. Anything under
+ * RETENTION_MIN_MS is treated as off: a fat-fingered `max_lifetime: 1000` (set
+ * from any client by anyone with state power) used to blank every timeline and
+ * get opted-in users' messages redacted within a minute.
+ */
+export const effectiveRetentionMs = (maxLifetime: unknown): number | undefined =>
+  typeof maxLifetime === 'number' && Number.isFinite(maxLifetime) && maxLifetime >= RETENTION_MIN_MS
+    ? maxLifetime
+    : undefined;
+
 /** 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;
+  return effectiveRetentionMs(event?.getContent<RetentionContent>()?.max_lifetime);
 };
 
+/**
+ * [Gitea #298] Deletion grace: the auto-delete sweeper ignores a retention
+ * policy for this long after it was set, so a mistaken or malicious change can
+ * be reverted before anything is permanently redacted. (Hiding expired
+ * messages locally is not destructive and applies at once.)
+ */
+export const RETENTION_DELETE_GRACE_MS = DAY_MS;
+
+export const retentionDeletesAllowed = (policySetAtMs: number, nowMs: number): boolean =>
+  nowMs - policySetAtMs >= RETENTION_DELETE_GRACE_MS;
+
+/** When the room's current retention policy was set (its state event's ts). */
+export const getRoomRetentionSetAt = (room: Room): number | undefined =>
+  room.currentState.getStateEvents(StateEvent.RoomRetention, '')?.getTs();
+
 /** 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;