Merge pull request 'fix(outbox): two tabs no longer overwrite each other's queue (#268)' (#430) from fix/outbox-multi-tab into lotus

OutboxFeature loaded lotus_outbox_v1 once and then saved its own
in-memory list over the key on every change, so a second tab's save
dropped the first tab's unsent messages. persist() now re-reads the
stored list and applies the change (add/remove by txnId) to it.

Fixes #268

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

src/app/features/bookmarks/BookmarksPanel.css.ts

@@ -1,10 +1,11 @@
 import { style } from '@vanilla-extract/css';
-import { config, toRem } from 'folds';
+import { config } from 'folds';
+import { SIDE_PANEL_WIDTH } from '../../styles/sidePanel';
 
-// Mirrors MembersDrawer: a 266px side panel on desktop that becomes a
+// Mirrors MembersDrawer: a side panel (shared width) on desktop that becomes a
 // full-screen fixed panel on narrow viewports — the app's canonical drawer.
 export const BookmarksPanel = style({
-  width: toRem(266),
+  width: SIDE_PANEL_WIDTH,
   '@media': {
     '(max-width: 750px)': {
       position: 'fixed',

src/app/features/outbox/OutboxFeature.tsx

@@ -94,10 +94,15 @@ export function OutboxFeature() {
       OFFLINE.has(mx.getSyncState()) ||
       (typeof navigator !== 'undefined' && navigator.onLine === false);
 
-    const persist = (next: OutboxEntry[]) => {
-      if (next === entries) return;
+    // [Gitea #268] Read-modify-write: another tab may have queued or cleared
+    // entries since we last looked, and saving our own copy over the key
+    // would drop theirs. Entries are added/removed by txnId, so applying our
+    // change to the stored list merges cleanly.
+    const persist = (update: (list: OutboxEntry[]) => OutboxEntry[]) => {
+      const stored = loadOutbox(userId);
+      const next = update(stored);
       entries = next;
-      saveOutbox(userId, entries);
+      if (next !== stored) saveOutbox(userId, next);
     };
 
     /**
@@ -123,8 +128,8 @@ export function OutboxFeature() {
         if (!shouldKeepInOutbox(event.getType(), event.getContent())) return;
         live.set(txnId, { event, room });
         if (event.status === EventStatus.NOT_SENT) scheduleBlipRetry(event);
-        persist(
-          withEntry(entries, {
+        persist((list) =>
+          withEntry(list, {
             txnId,
             roomId: room.roomId,
             threadId: event.threadRootId ?? null,
@@ -138,7 +143,7 @@ export function OutboxFeature() {
       // SENT, CANCELLED, or the remote echo replaced it (status null).
       live.delete(txnId);
       autoRetries.delete(txnId);
-      persist(withoutEntry(entries, txnId));
+      persist((list) => withoutEntry(list, txnId));
     };
 
     /** Re-send network failures, oldest first; a room stops at its first failure. */
@@ -191,7 +196,7 @@ export function OutboxFeature() {
           return !!room && isDelivered(room, entry.txnId);
         },
       );
-      plan.drop.forEach((entry) => persist(withoutEntry(entries, entry.txnId)));
+      plan.drop.forEach((entry) => persist((list) => withoutEntry(list, entry.txnId)));
       plan.restore.forEach((entry) => {
         const room = mx.getRoom(entry.roomId);
         if (!room || live.has(entry.txnId)) return;

src/app/features/room-settings/RoomServerACL.tsx

@@ -32,24 +32,12 @@ import { AsyncStatus, useAsyncCallback } from '../../hooks/useAsyncCallback';
 import { SequenceCard } from '../../components/sequence-card';
 import { SequenceCardStyle } from '../common-settings/styles.css';
 import { stopPropagation } from '../../utils/keyboard';
-import { isValidServerPattern, matchesAnyGlob } from '../../utils/serverAcl';
+import { isValidServerPattern, matchesAnyGlob, normalizeServerAcl } from '../../utils/serverAcl';
 import { MobileTouchTarget } from '../../styles/mobile.css';
 import { useModalStyle } from '../../hooks/useModalStyle';
 
 // ── Types ─────────────────────────────────────────────────────────────────────
 
-type ServerAclContent = {
-  allow: string[];
-  deny: string[];
-  allow_ip_literals: boolean;
-};
-
-const DEFAULT_ACL: ServerAclContent = {
-  allow: ['*'],
-  deny: [],
-  allow_ip_literals: false,
-};
-
 // ── Server list sub-component ─────────────────────────────────────────────────
 
 type ServerListProps = {
@@ -185,20 +173,20 @@ export function RoomServerACL({ requestClose }: RoomServerACLProps) {
 
   // Read current ACL from room state
   const aclEvent = useStateEvent(room, StateEvent.RoomServerAcl);
-  const currentAcl = aclEvent?.getContent<ServerAclContent>() ?? DEFAULT_ACL;
+  const currentAcl = normalizeServerAcl(aclEvent?.getContent());
 
   // Local draft state — initialised from current ACL
-  const [allowList, setAllowList] = useState<string[]>(() => currentAcl.allow ?? ['*']);
-  const [denyList, setDenyList] = useState<string[]>(() => currentAcl.deny ?? []);
+  const [allowList, setAllowList] = useState<string[]>(() => currentAcl.allow);
+  const [denyList, setDenyList] = useState<string[]>(() => currentAcl.deny);
   const [allowIpLiterals, setAllowIpLiterals] = useState<boolean>(
-    () => currentAcl.allow_ip_literals ?? false,
+    () => currentAcl.allow_ip_literals,
   );
 
   // Track whether there are unsaved changes
   const isDirty =
-    JSON.stringify(allowList) !== JSON.stringify(currentAcl.allow ?? ['*']) ||
-    JSON.stringify(denyList) !== JSON.stringify(currentAcl.deny ?? []) ||
-    allowIpLiterals !== (currentAcl.allow_ip_literals ?? false);
+    JSON.stringify(allowList) !== JSON.stringify(currentAcl.allow) ||
+    JSON.stringify(denyList) !== JSON.stringify(currentAcl.deny) ||
+    allowIpLiterals !== currentAcl.allow_ip_literals;
 
   // Save handler
   const [saveState, save] = useAsyncCallback(
@@ -336,7 +324,10 @@ export function RoomServerACL({ requestClose }: RoomServerACLProps) {
                       id="allow-ip-literals"
                       checked={allowIpLiterals}
                       disabled={!canEdit}
-                      onClick={() => setAllowIpLiterals(!allowIpLiterals)}
+                      // folds' Checkbox has no onChange; readOnly tells React the
+                      // click handler controls it (no "checked without onChange").
+                      readOnly
+                      onClick={(e) => setAllowIpLiterals(e.currentTarget.checked)}
                       size="300"
                       variant="Primary"
                     />

src/app/features/room/MediaGallery.css.ts

@@ -1,13 +1,13 @@
 import { style } from '@vanilla-extract/css';
 import { color, config, toRem } from 'folds';
+import { SIDE_PANEL_WIDTH } from '../../styles/sidePanel';
 
 // Right-side drawer DOCKED into the room layout row (a flex sibling of the
-// timeline), exactly like MembersDrawer — not a floating overlay. 320px is a
-// little wider than the 266px member/bookmark drawers because it hosts a media
-// grid. On narrow viewports it becomes a full-screen fixed panel, matching the
-// app's other drawers.
+// timeline), exactly like MembersDrawer — not a floating overlay. Same width as
+// every other right-hand panel (styles/sidePanel.ts, #263). On narrow viewports
+// it becomes a full-screen fixed panel, matching the app's other drawers.
 export const MediaGalleryDrawer = style({
-  width: toRem(320),
+  width: SIDE_PANEL_WIDTH,
   overflow: 'hidden',
   '@media': {
     '(max-width: 750px)': {

src/app/features/room/MembersDrawer.css.ts

@@ -1,8 +1,9 @@
 import { keyframes, style } from '@vanilla-extract/css';
-import { config, toRem } from 'folds';
+import { config } from 'folds';
+import { SIDE_PANEL_WIDTH } from '../../styles/sidePanel';
 
 export const MembersDrawer = style({
-  width: toRem(266),
+  width: SIDE_PANEL_WIDTH,
   '@media': {
     '(max-width: 750px)': {
       position: 'fixed',

src/app/features/room/thread/ThreadPanel.css.ts

@@ -1,8 +1,9 @@
 import { style } from '@vanilla-extract/css';
-import { config, toRem } from 'folds';
+import { config } from 'folds';
+import { SIDE_PANEL_WIDTH } from '../../../styles/sidePanel';
 
 export const ThreadPanel = style({
-  width: toRem(360),
+  width: SIDE_PANEL_WIDTH,
   '@media': {
     '(max-width: 750px)': {
       position: 'fixed',

src/app/features/room/thread/ThreadsListPanel.css.ts

@@ -1,8 +1,9 @@
 import { style } from '@vanilla-extract/css';
-import { color, config, toRem } from 'folds';
+import { color, config } from 'folds';
+import { SIDE_PANEL_WIDTH } from '../../../styles/sidePanel';
 
 export const ThreadsListPanel = style({
-  width: toRem(340),
+  width: SIDE_PANEL_WIDTH,
   '@media': {
     '(max-width: 750px)': {
       position: 'fixed',

src/app/features/room/widgets/WidgetsPanel.css.ts

@@ -1,8 +1,9 @@
 import { style } from '@vanilla-extract/css';
-import { config, toRem } from 'folds';
+import { config } from 'folds';
+import { SIDE_PANEL_WIDTH } from '../../../styles/sidePanel';
 
 export const WidgetsPanel = style({
-  width: toRem(360),
+  width: SIDE_PANEL_WIDTH,
   '@media': {
     '(max-width: 750px)': {
       position: 'fixed',

src/app/features/room/widgets/widgetUtils.test.ts

@@ -106,3 +106,19 @@ test('classifyWidgetCapabilities: reading protected state is fine, changing unpr
 test('loadWidgetConsent tolerates missing storage', () => {
   assert.equal(loadWidgetConsent('!r:x', 'w', 'https://w.example'), undefined);
 });
+
+test('[#266] space structure, call membership and Lotus room policy can never be granted', () => {
+  const { auto, ask } = classifyWidgetCapabilities(
+    [
+      'm.space.child',
+      'm.space.parent',
+      'org.matrix.msc3401.call',
+      'org.matrix.msc3401.call.member',
+      'm.call.member',
+      'io.lotus.voice_limit',
+      'io.lotus.room_quality',
+    ].map((t) => `org.matrix.msc2762.send.state_event:${t}`),
+  );
+  assert.equal(auto.size, 0);
+  assert.deepEqual(ask, []);
+});

src/app/features/room/widgets/widgetUtils.ts

@@ -67,6 +67,16 @@ export const PROTECTED_STATE_TYPES: ReadonlySet<string> = new Set([
   'm.room.third_party_invite',
   'im.vector.modular.widgets',
   'm.widget',
+  // [Gitea #266] Space structure, call membership and Lotus room policy: a
+  // widget could restructure a space, fake call membership or lift the
+  // voice-channel limit, so these can't be granted even with consent.
+  'm.space.child',
+  'm.space.parent',
+  'org.matrix.msc3401.call',
+  'org.matrix.msc3401.call.member',
+  'm.call.member',
+  'io.lotus.voice_limit',
+  'io.lotus.room_quality',
 ]);
 
 export type WidgetPermissionRequest = {
@@ -137,8 +147,11 @@ export const classifyWidgetCapabilities = (
  */
 export type StoredWidgetConsent = { url: string; allowed: Capability[]; denied: Capability[] };
 
+// [Gitea #266] Swept on logout by clearPlaintextCaches, so one account's
+// approvals never apply to the next account on the same device.
+export const WIDGET_CONSENT_PREFIX = 'lotus.widgetConsent.';
 export const widgetConsentKey = (roomId: string, widgetId: string): string =>
-  `lotus.widgetConsent.${roomId}.${widgetId}`;
+  `${WIDGET_CONSENT_PREFIX}${roomId}.${widgetId}`;
 
 export const loadWidgetConsent = (
   roomId: string,

src/app/pages/client/ClientRoot.tsx

@@ -33,6 +33,8 @@ import {
 } from '../../../client/initMatrix';
 import { deleteSearchCacheDatabase } from '../../utils/searchCache';
 import { clearPlaintextCaches } from '../../state/plaintextCaches';
+import { clearSoundboardClipCache } from '../../utils/soundboardClips';
+import { clearSharedPayload } from '../../../swShare';
 import { SplashScreen } from '../../components/splash-screen';
 import { ServerConfigsLoader } from '../../components/ServerConfigsLoader';
 import { CapabilitiesProvider } from '../../hooks/useCapabilities';
@@ -172,6 +174,10 @@ const useLogoutListener = (mx?: MatrixClient) => {
       // (translation, scheduled messages, recent searches/forwards/gifs/
       // stickers, nav paths) — wipe them on server-forced logout too.
       clearPlaintextCaches(mx?.getUserId() ?? undefined);
+      // [Gitea #57] As on manual logout: no decrypted clip bytes via blob: URLs.
+      clearSoundboardClipCache();
+      // [Gitea #267] As on manual logout: drop files stashed by the share target.
+      await clearSharedPayload().catch(() => undefined);
       // Remove only the session credential keys — NOT settings, drafts, and
       // other preferences (N98). The SDK's IndexedDB stores are cleared above;
       // window.localStorage.clear() is reserved for the explicit reset path.

src/app/pages/client/share/Share.tsx

@@ -145,6 +145,11 @@ export function Share() {
               <Box direction="Column" gap="400">
                 <Box direction="Column" gap="200">
                   <Text size="L400">Shared</Text>
+                  {/* [Gitea #267] Not everything that arrives here came from the
+                      user's share sheet; say so before they pick a room. */}
+                  <Text size="T200" priority="300">
+                    This came from another app or website. Check it before you send it.
+                  </Text>
                   {shared.files.map((f) => (
                     <Box key={f.name} alignItems="Center" gap="200">
                       <Icon

src/app/state/plaintextCaches.test.ts

@@ -26,7 +26,10 @@ const api = {
       : Object.getOwnPropertyDescriptor(target, key),
 });
 
-const { clearPlaintextCaches, plaintextCachesWiped } = await import('./plaintextCaches');
+const { clearPlaintextCaches, plaintextCachesWiped, WIDGET_CONSENT_KEY_PREFIX } =
+  await import('./plaintextCaches');
+const { WIDGET_CONSENT_PREFIX, widgetConsentKey } =
+  await import('../features/room/widgets/widgetUtils');
 
 test('clearPlaintextCaches removes every plaintext/PII localStorage key', () => {
   store.clear();
@@ -104,3 +107,17 @@ test('clearPlaintextCaches clears the encrypted-search opt-in and flags the wipe
   assert.equal(store.has('mxjssdk_memory_filter_FILTER_SYNC_@me:server'), false);
   assert.equal(plaintextCachesWiped(), true, 'draft writes stop until the page reloads');
 });
+
+test('[#266] clearPlaintextCaches sweeps remembered widget approvals', () => {
+  assert.equal(WIDGET_CONSENT_KEY_PREFIX, WIDGET_CONSENT_PREFIX, 'prefix kept in sync');
+  store.clear();
+  const consent = widgetConsentKey('!room:server', 'widget-1');
+  store.set(consent, '{"url":"https://pad.example","allowed":[],"denied":[]}');
+  store.set('lotus.widgetConsentNotAKey', 'kept');
+  removed.length = 0;
+
+  clearPlaintextCaches('@me:server');
+
+  assert.ok(removed.includes(consent), 'consent cleared');
+  assert.ok(store.has('lotus.widgetConsentNotAKey'), 'unrelated key kept');
+});

src/app/state/plaintextCaches.ts

@@ -139,6 +139,31 @@ const clearAccountScopedFlags = (userId?: string): void => {
   });
 };
 
+/**
+ * [Gitea #266] Remembered widget approvals (`lotus.widgetConsent.<room>.<widget>`,
+ * widgetUtils.ts) would otherwise apply silently to the next account on this
+ * device, and their keys list the previous account's rooms. Kept as a string
+ * here so logout doesn't pull the widget code into the entry chunk; a test
+ * checks it matches WIDGET_CONSENT_PREFIX.
+ */
+export const WIDGET_CONSENT_KEY_PREFIX = 'lotus.widgetConsent.';
+const clearWidgetConsents = (): void => {
+  let keys: string[];
+  try {
+    keys = Object.keys(localStorage);
+  } catch {
+    return;
+  }
+  keys.forEach((key) => {
+    if (!key.startsWith(WIDGET_CONSENT_KEY_PREFIX)) return;
+    try {
+      localStorage.removeItem(key);
+    } catch {
+      // best-effort
+    }
+  });
+};
+
 export const clearPlaintextCaches = (userId?: string): void => {
   wiped = true;
   clearTranslationCache();
@@ -153,5 +178,6 @@ export const clearPlaintextCaches = (userId?: string): void => {
   clearStatusMessage();
   clearCallVolumesAndSyncMeta(userId);
   clearAccountScopedFlags(userId);
+  clearWidgetConsents();
   if (userId) clearNavToActivePathStore(userId);
 };

src/app/styles/sidePanel.ts

@@ -0,0 +1,9 @@
+import { toRem } from 'folds';
+
+/**
+ * One width for every right-hand room panel (members, bookmarks, threads, a
+ * thread, media gallery, widgets). Swapping one panel for another must not
+ * resize the room view: when the widths differed, the header icons slid
+ * sideways and a second click on the same spot hit a different button (#263).
+ */
+export const SIDE_PANEL_WIDTH = toRem(340);

src/app/utils/serverAcl.test.ts

@@ -1,6 +1,11 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
-import { isValidServerPattern, globToRegExp, matchesAnyGlob } from './serverAcl';
+import {
+  isValidServerPattern,
+  globToRegExp,
+  matchesAnyGlob,
+  normalizeServerAcl,
+} from './serverAcl';
 
 test('isValidServerPattern: accepts hostnames, IPs, and globs', () => {
   for (const v of [
@@ -42,3 +47,35 @@ test('matchesAnyGlob: true if any glob matches (self-ban detection)', () => {
   assert.equal(matchesAnyGlob('lotusguild.org', ['*.evil.com']), false);
   assert.equal(matchesAnyGlob('lotusguild.org', []), false);
 });
+
+test('no ACL event: every server allowed, IP literals allowed (#261)', () => {
+  assert.deepEqual(normalizeServerAcl(undefined), {
+    allow: ['*'],
+    deny: [],
+    allow_ip_literals: true,
+  });
+});
+
+test('a missing allow_ip_literals defaults to true, per the spec (#261)', () => {
+  assert.equal(normalizeServerAcl({ allow: ['*'], deny: ['bad.example'] }).allow_ip_literals, true);
+});
+
+test('an explicit allow_ip_literals is kept', () => {
+  assert.equal(
+    normalizeServerAcl({ allow: ['*'], allow_ip_literals: false }).allow_ip_literals,
+    false,
+  );
+  assert.equal(
+    normalizeServerAcl({ allow: ['*'], allow_ip_literals: true }).allow_ip_literals,
+    true,
+  );
+});
+
+test('missing or malformed lists become empty, non-strings are dropped', () => {
+  assert.deepEqual(normalizeServerAcl({ allow: ['a.example', 3, null] }), {
+    allow: ['a.example'],
+    deny: [],
+    allow_ip_literals: true,
+  });
+  assert.deepEqual(normalizeServerAcl({ allow: 'a.example', deny: {} }).allow, []);
+});

src/app/utils/serverAcl.ts

@@ -50,3 +50,29 @@ export function matchesAnyGlob(domain: string, globs: string[]): boolean {
     }
   });
 }
+
+/**
+ * `m.room.server_acl` content with the spec's defaults filled in (#261).
+ * `allow_ip_literals` defaults to **true** when absent; `allow` and `deny`
+ * default to empty lists, but with no ACL event at all every server is allowed,
+ * so the editor starts from `allow: ['*']` in that case.
+ * https://spec.matrix.org/v1.12/client-server-api/#mroomserver_acl
+ */
+export type ServerAclContent = {
+  allow: string[];
+  deny: string[];
+  allow_ip_literals: boolean;
+};
+
+const stringList = (value: unknown): string[] | undefined =>
+  Array.isArray(value) ? value.filter((v): v is string => typeof v === 'string') : undefined;
+
+export function normalizeServerAcl(content: Record<string, unknown> | undefined): ServerAclContent {
+  if (!content) return { allow: ['*'], deny: [], allow_ip_literals: true };
+  return {
+    allow: stringList(content.allow) ?? [],
+    deny: stringList(content.deny) ?? [],
+    allow_ip_literals:
+      typeof content.allow_ip_literals === 'boolean' ? content.allow_ip_literals : true,
+  };
+}

src/client/initMatrix.ts

@@ -9,6 +9,7 @@ import { pushSessionToSW } from '../sw-session';
 import { deleteSearchCacheDatabase, shouldRunBootCleanup } from '../app/utils/searchCache';
 import { clearPlaintextCaches } from '../app/state/plaintextCaches';
 import { clearSoundboardClipCache } from '../app/utils/soundboardClips';
+import { clearSharedPayload } from '../swShare';
 
 // Thrown when the local IndexedDB has a higher schema version than this SDK expects.
 // This happens after a downgrade (e.g. matrix-js-sdk was briefly upgraded and then reverted).
@@ -146,6 +147,9 @@ export const logoutClient = async (mx: MatrixClient) => {
   // [Gitea #57] Same reasoning as clearPlaintextCaches: decrypted soundboard
   // clip bytes stay reachable via live blob: URLs until the reload otherwise.
   clearSoundboardClipCache();
+  // [Gitea #267] Files stashed by the share target stay in Cache Storage until
+  // /share is opened; a shared photo must not outlive the logout.
+  await clearSharedPayload().catch(() => undefined);
   // Remove only the session credential keys, preserving user preferences and
   // unsent drafts (N98). The factory-reset path is clearLoginData() below.
   removeFallbackSession();

src/sw.ts

@@ -1,7 +1,7 @@
 /// <reference lib="WebWorker" />
 
 import { precacheAndRoute, type PrecacheEntry } from 'workbox-precaching';
-import { SHARE_TARGET_PATH, stashSharedForm } from './swShare';
+import { isTrustedShareRequest, SHARE_TARGET_PATH, stashSharedForm } from './swShare';
 import { pickReplySession, replyFailureText, sendNotificationReply } from './swReply';
 
 export type {};
@@ -249,6 +249,11 @@ self.addEventListener('fetch', (event: FetchEvent) => {
   // share_target). Stash the form and bounce to the in-app /share page.
   if (method === 'POST' && new URL(url).pathname.endsWith(SHARE_TARGET_PATH)) {
     const base = new URL(url).pathname.slice(0, -SHARE_TARGET_PATH.length);
+    // [Gitea #267] A cross-site form posting here is not a share: drop it.
+    if (!isTrustedShareRequest(event.request.headers, self.location.origin)) {
+      event.respondWith(Response.redirect(`${base}/`, 303));
+      return;
+    }
     event.respondWith(
       stashSharedForm(event.request, base).catch(() => Response.redirect(`${base}/`, 303)),
     );

src/swShare.test.ts

@@ -1,6 +1,6 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
-import { shareDraftText } from './swShare';
+import { isTrustedShareRequest, shareDraftText } from './swShare';
 
 const base = { files: [], receivedAt: 0 };
 
@@ -25,3 +25,14 @@ test('shareDraftText drops a title/url the text already contains', () => {
   assert.equal(shareDraftText({ ...base, url: 'https://x.test' }), 'https://x.test');
   assert.equal(shareDraftText(base), '');
 });
+
+test('[#267] a share another website submitted is refused', () => {
+  const app = 'https://chat.lotusguild.org';
+  const h = (origin?: string) => new Headers(origin ? { Origin: origin } : {});
+  assert.equal(isTrustedShareRequest(h(), app), true, 'no Origin (OS share sheet)');
+  assert.equal(isTrustedShareRequest(h('null'), app), true, 'opaque origin (OS share sheet)');
+  assert.equal(isTrustedShareRequest(h(app), app), true, 'the app itself');
+  assert.equal(isTrustedShareRequest(h('https://evil.example'), app), false);
+  assert.equal(isTrustedShareRequest(h('https://chat.lotusguild.org.evil.example'), app), false);
+  assert.equal(isTrustedShareRequest(h('http://chat.lotusguild.org'), app), false, 'other scheme');
+});

src/swShare.ts

@@ -20,6 +20,27 @@ export type SharePayload = {
   receivedAt: number;
 };
 
+/**
+ * [Gitea #267] Refuse a share that another website submitted: any site could
+ * otherwise auto-submit a cross-site form here and drop attacker-chosen text
+ * and files into the "Share to…" picker as if the user had shared them.
+ *
+ * The worker can't use `Sec-Fetch-Site`: fetch-metadata headers are added
+ * after the service worker and never appear on `event.request` (checked in
+ * Chromium). `Origin` does: a cross-site form carries the site's origin. The
+ * OS share sheet's POST has no web initiator, so its Origin is `null` or
+ * absent, and both stay accepted. A page can also produce `Origin: null`
+ * (sandboxed frame, no-referrer), which is why /share also says the content
+ * came from elsewhere.
+ */
+export const isTrustedShareRequest = (
+  headers: Pick<Headers, 'get'>,
+  selfOrigin: string,
+): boolean => {
+  const origin = headers.get('Origin');
+  return origin === null || origin === 'null' || origin === selfOrigin;
+};
+
 /** Worker side: stash the POSTed form and answer with a redirect to /share. */
 export async function stashSharedForm(request: Request, base: string): Promise<Response> {
   const form = await request.formData();