feat: offline outbox — unsent messages survive reload and retry (#112)

Until now a send that failed (offline, homeserver down, a blip) went
straight to "Failed to send": nothing retried it, and a reload dropped it
without trace (chronological pending ordering keeps local echoes in memory
only).

- Outbox (utils/outbox.ts + features/outbox/OutboxFeature): own message
  sends (text, stickers, reactions, polls; not call signalling or
  redactions) are mirrored to localStorage from their first local echo until
  the server confirms them or the user cancels.
- After a reload they come back as local echoes via room.addPendingEvent,
  same shape as the SDK's own. Recent ones (< 1 h) are sent again with the
  same txnId; older ones come back as "Failed to send" for the user to
  retry or cancel. Ones the server already has (transaction id seen in
  /sync) are dropped, so no duplicates.
- Retries: network failures (ConnectionError, 408/429/5xx) are re-sent when
  the connection returns (sync recovers or the browser goes back online),
  and after a blip while online (5 s, backing off, max 10 per message).
  Oldest first, in order per room. 4xx / consent / encryption failures are
  left to the user.
- UI: a network failure while offline shows a clock, "Queued. Will send
  when you're back online" (thread view too), not the red ✕. The ✕ is now
  a button: click to retry.
- Logout wipes the outbox with the other plaintext caches (the content is
  decrypted, like drafts).

Tested end to end against a local Synapse (Chromium): offline → queued →
sent once on reconnect; homeserver unreachable → queued → sent once; failed
send → reload → sent once and shown once; server accepted but response lost
→ reload → no duplicate; 2 h old entry → failed, not sent, click ✕ → sent;
cancel → gone after reload; encrypted room → restored message goes out as
m.room.encrypted with no plaintext and decrypts; one-off failure retried by
itself in ~5 s; no page errors. Unit tests for the pure parts; Playwright
20 passed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/features/outbox/OutboxFeature.tsx

@@ -0,0 +1,268 @@
+import { useSetAtom } from 'jotai';
+import { useEffect } from 'react';
+import {
+  ClientEvent,
+  ClientEventHandlerMap,
+  ConnectionError,
+  EventStatus,
+  KnownMembership,
+  MatrixClient,
+  MatrixError,
+  MatrixEvent,
+  Room,
+  RoomEvent,
+  RoomEventHandlerMap,
+  SyncState,
+} from 'matrix-js-sdk';
+import { useMatrixClient } from '../../hooks/useMatrixClient';
+import { sendOfflineAtom } from '../../state/sendOffline';
+import {
+  OUTBOX_MAX_AUTO_RETRIES,
+  OutboxEntry,
+  isRetryableSendError,
+  loadOutbox,
+  outboxRetryDelayMs,
+  planRestore,
+  saveOutbox,
+  shouldKeepInOutbox,
+  withEntry,
+  withoutEntry,
+} from '../../utils/outbox';
+
+const PENDING: ReadonlySet<EventStatus | null> = new Set([
+  EventStatus.SENDING,
+  EventStatus.ENCRYPTING,
+  EventStatus.QUEUED,
+  EventStatus.NOT_SENT,
+]);
+const ONLINE: ReadonlySet<SyncState | null> = new Set([
+  SyncState.Prepared,
+  SyncState.Syncing,
+  SyncState.Catchup,
+]);
+const OFFLINE: ReadonlySet<SyncState | null> = new Set([SyncState.Reconnecting, SyncState.Error]);
+
+/** The server already has it: its transaction id came back down /sync. */
+const isDelivered = (room: Room, txnId: string): boolean => {
+  const hasTxn = (events: MatrixEvent[]) =>
+    events.some((e) => e.getUnsigned().transaction_id === txnId);
+  return (
+    hasTxn(room.getLiveTimeline().getEvents()) ||
+    room.getThreads().some((t) => hasTxn(t.liveTimeline.getEvents()))
+  );
+};
+
+type OutboxSession = {
+  /** Own pending events of this session, by txnId. */
+  live: Map<string, { event: MatrixEvent; room: Room }>;
+  autoRetries: Map<string, number>;
+  restored: boolean;
+  retrying: boolean;
+};
+
+// Per client, not per mount: a remount must neither restore twice nor forget
+// the events it is tracking.
+const sessions = new WeakMap<MatrixClient, OutboxSession>();
+const getSession = (mx: MatrixClient): OutboxSession => {
+  let session = sessions.get(mx);
+  if (!session) {
+    session = { live: new Map(), autoRetries: new Map(), restored: false, retrying: false };
+    sessions.set(mx, session);
+  }
+  return session;
+};
+
+/**
+ * [Gitea #112] Offline outbox (see utils/outbox.ts): mirrors own message sends
+ * into localStorage until the server confirms them, puts unsent ones back
+ * after a reload, and re-sends network failures when the connection returns.
+ */
+export function OutboxFeature() {
+  const mx = useMatrixClient();
+  const setOffline = useSetAtom(sendOfflineAtom);
+
+  useEffect(() => {
+    const userId = mx.getSafeUserId();
+    let entries = loadOutbox(userId);
+    const session = getSession(mx);
+    const { live, autoRetries } = session;
+    let disposed = false;
+    let offlineNow = false;
+    const timers = new Set<ReturnType<typeof setTimeout>>();
+
+    const isOffline = () =>
+      OFFLINE.has(mx.getSyncState()) ||
+      (typeof navigator !== 'undefined' && navigator.onLine === false);
+
+    const persist = (next: OutboxEntry[]) => {
+      if (next === entries) return;
+      entries = next;
+      saveOutbox(userId, entries);
+    };
+
+    /**
+     * A network failure while we think we're online (a blip neither sync nor
+     * the browser noticed): try again shortly, backing off. Real outages are
+     * handled by the reconnect / back-online triggers below.
+     */
+    const scheduleBlipRetry = (event: MatrixEvent) => {
+      const attempts = autoRetries.get(event.getTxnId() ?? '') ?? 0;
+      if (!isRetryableSendError(event.error) || attempts >= OUTBOX_MAX_AUTO_RETRIES || isOffline())
+        return;
+      const timer = setTimeout(() => {
+        timers.delete(timer);
+        retryQueued();
+      }, outboxRetryDelayMs(attempts));
+      timers.add(timer);
+    };
+
+    const onLocalEcho: RoomEventHandlerMap[RoomEvent.LocalEchoUpdated] = (event, room) => {
+      const txnId = event.getTxnId();
+      if (!txnId || event.getSender() !== userId) return;
+      if (PENDING.has(event.status)) {
+        if (!shouldKeepInOutbox(event.getType(), event.getContent())) return;
+        live.set(txnId, { event, room });
+        if (event.status === EventStatus.NOT_SENT) scheduleBlipRetry(event);
+        persist(
+          withEntry(entries, {
+            txnId,
+            roomId: room.roomId,
+            threadId: event.threadRootId ?? null,
+            type: event.getType(),
+            content: event.getContent(),
+            ts: event.getTs(),
+          }),
+        );
+        return;
+      }
+      // SENT, CANCELLED, or the remote echo replaced it (status null).
+      live.delete(txnId);
+      autoRetries.delete(txnId);
+      persist(withoutEntry(entries, txnId));
+    };
+
+    /** Re-send network failures, oldest first; a room stops at its first failure. */
+    const retryQueued = async () => {
+      if (session.retrying || disposed) return;
+      session.retrying = true;
+      try {
+        const byRoom = new Map<Room, MatrixEvent[]>();
+        Array.from(live.values())
+          .filter(
+            ({ event }) =>
+              event.status === EventStatus.NOT_SENT &&
+              isRetryableSendError(event.error) &&
+              (autoRetries.get(event.getTxnId() ?? '') ?? 0) < OUTBOX_MAX_AUTO_RETRIES,
+          )
+          .sort((a, b) => a.event.getTs() - b.event.getTs())
+          .forEach(({ event, room }) => {
+            byRoom.set(room, [...(byRoom.get(room) ?? []), event]);
+          });
+        await Promise.all(
+          Array.from(byRoom.entries()).map(async ([room, events]) => {
+            for (const event of events) {
+              if (disposed || event.status !== EventStatus.NOT_SENT) continue;
+              const txnId = event.getTxnId() ?? '';
+              autoRetries.set(txnId, (autoRetries.get(txnId) ?? 0) + 1);
+              try {
+                // eslint-disable-next-line no-await-in-loop
+                await mx.resendEvent(event, room);
+              } catch (e) {
+                // Still offline: keep the rest of this room in order for the next try.
+                if (isRetryableSendError(e)) break;
+              }
+            }
+          }),
+        );
+      } finally {
+        session.retrying = false;
+      }
+    };
+
+    const restore = () => {
+      if (session.restored) return;
+      session.restored = true;
+      const plan = planRestore(
+        entries,
+        Date.now(),
+        (roomId) => mx.getRoom(roomId)?.getMyMembership() === KnownMembership.Join,
+        (entry) => {
+          const room = mx.getRoom(entry.roomId);
+          return !!room && isDelivered(room, entry.txnId);
+        },
+      );
+      plan.drop.forEach((entry) => persist(withoutEntry(entries, entry.txnId)));
+      plan.restore.forEach((entry) => {
+        const room = mx.getRoom(entry.roomId);
+        if (!room || live.has(entry.txnId)) return;
+        // Same shape as the SDK's own local echo (client.sendCompleteEvent).
+        const event = new MatrixEvent({
+          type: entry.type,
+          content: entry.content,
+          event_id: `~${entry.roomId}:${entry.txnId}`,
+          sender: userId,
+          room_id: entry.roomId,
+          origin_server_ts: entry.ts,
+        });
+        const thread = entry.threadId ? room.getThread(entry.threadId) : undefined;
+        if (thread) event.setThread(thread);
+        event.setTxnId(entry.txnId);
+        event.setStatus(EventStatus.NOT_SENT);
+        if (plan.autoSend.has(entry.txnId)) {
+          // Recent: treat like a send that lost the network (shown as Queued
+          // while offline, re-sent below and on reconnect).
+          // (The SDK types `error` as MatrixError but stores any send error there.)
+          event.error = new ConnectionError(
+            'not sent before the app was closed',
+          ) as unknown as MatrixError;
+        } else {
+          // Old: back as "Failed to send"; the user decides (Retry / Cancel).
+          autoRetries.set(entry.txnId, OUTBOX_MAX_AUTO_RETRIES);
+        }
+        try {
+          room.addPendingEvent(event, entry.txnId); // emits LocalEchoUpdated → `live`
+        } catch {
+          // Already pending under this txnId: nothing to restore.
+        }
+      });
+      if (!isOffline()) retryQueued();
+    };
+
+    const updateOffline = () => {
+      const offline = isOffline();
+      // Back online (sync recovered or the browser says so): send what's queued.
+      if (offlineNow && !offline && session.restored) retryQueued();
+      offlineNow = offline;
+      setOffline(offline);
+    };
+
+    const onSync: ClientEventHandlerMap[ClientEvent.Sync] = (state, prevState) => {
+      updateOffline();
+      if (!ONLINE.has(state)) return;
+      if (!session.restored) {
+        restore();
+        return;
+      }
+      if (OFFLINE.has(prevState) || prevState === SyncState.Catchup) retryQueued();
+    };
+    const onBrowserOnline = () => updateOffline();
+
+    mx.on(RoomEvent.LocalEchoUpdated, onLocalEcho);
+    mx.on(ClientEvent.Sync, onSync);
+    window.addEventListener('online', onBrowserOnline);
+    window.addEventListener('offline', onBrowserOnline);
+    updateOffline();
+    if (ONLINE.has(mx.getSyncState())) restore();
+
+    return () => {
+      disposed = true;
+      timers.forEach((t) => clearTimeout(t));
+      mx.off(RoomEvent.LocalEchoUpdated, onLocalEcho);
+      mx.off(ClientEvent.Sync, onSync);
+      window.removeEventListener('online', onBrowserOnline);
+      window.removeEventListener('offline', onBrowserOnline);
+    };
+  }, [mx, setOffline]);
+
+  return null;
+}