docs(todo): redirect to sign-in on session timeout instead of hanging

Captured from Gate 2 live testing: when the OIDC session expires mid-use, the
app hangs the action and shows a generic 'couldn't load events' instead of
recognizing the signed-out state and redirecting to /api/login. Re-auth is
currently only wired to the initial /api/me failure (one-shot).

.planning/todos/pending/session-timeout-redirect-to-signin.md

@@ -0,0 +1,71 @@
+---
+title: Redirect to sign-in on session timeout instead of hanging / "couldn't load events"
+date: 2026-06-07
+priority: high
+phase_hint: Phase 03 (auth-entry UX) / Gate 2 polish
+---
+
+# Redirect to sign-in on session timeout instead of hanging
+
+## Problem (observed in live Gate 2 testing)
+
+When the OIDC session expires **mid-use** (e.g. user leaves the tab open past
+the session/refresh lifespan, then tries to delete an event), the app does not
+recognize the signed-out state. The action (delete) appears to hang — no sync
+toast, no progress — and shortly after the calendar shows a generic
+**"couldn't load events"** error. The user is fooled into thinking the app is
+working/broken rather than understanding they've been signed out and need to
+re-authenticate.
+
+## Root cause
+
+Re-auth is only wired to the **initial** `/api/me` failure:
+- `CalendarShell.tsx` calls `maybeRedirectToLogin()` only on `meQuery.isError`.
+- `maybeRedirectToLogin()` (apps/pwa/src/lib/loginRedirect.ts) is **one-shot**
+  (guarded by the `familysync.loginRedirectAttempted` sessionStorage flag) and
+  `clearLoginRedirect()` runs on a successful `/api/me`.
+- Other calls don't drive re-auth:
+  - `fetchEvents` uses `redirect: 'follow'`, so a timed-out session 302s to
+    Authelia (cross-origin) → the XHR rejects → `eventsQuery` just errors
+    ("couldn't load events"), no redirect.
+  - Write mutations (create/edit/**delete**) call the API directly; on an
+    expired session the request 302s/opaque-fails and the mutation hangs/errors
+    with no re-auth and no clear feedback.
+
+So a session that expires after the first successful load has no path back to
+login except a manual full refresh.
+
+## Desired behavior
+
+Any API response that indicates "not authenticated anymore" (401, or an
+`opaqueredirect`/`type: 'opaqueredirect'` from the OIDC guard's 302 to Authelia)
+should put the app into a clear **signed-out** state and trigger a top-level
+re-auth navigation to `/api/login` — from ANY query or mutation, not just the
+initial `/api/me`. The user should never be left staring at a hung action or a
+generic data-load error when the real cause is an expired session.
+
+## Scope to decide when promoted
+
+- Centralize auth-expiry detection in the API client (apps/pwa/src/api/client.ts):
+  a shared helper that classifies a response as "session expired" (401 or
+  opaqueredirect) and throws a typed `SessionExpiredError`.
+- Apply `redirect: 'manual'` consistently (fetchEvents/mutations) so the guard's
+  302 is detectable instead of hanging on the cross-origin follow.
+- A single TanStack Query handler (e.g. QueryCache/MutationCache `onError`, or
+  a small auth-state listener) that, on `SessionExpiredError`, calls a
+  re-armed `maybeRedirectToLogin()` — the one-shot loop guard must be reset so
+  a genuine later expiry can redirect again (clear the flag on detected expiry,
+  not only on successful `/api/me`).
+- Decide UX: immediate redirect to `/api/login` vs a brief "Your session
+  expired — signing you back in…" toast/interstitial before redirecting (the
+  non-technical Apple member should not see a raw error).
+- Make sure an in-flight write that fails on expiry is not silently lost — after
+  re-auth, either resurface the unsaved action or clearly tell the user it
+  wasn't saved (ties to T-03-18 no-silent-loss).
+
+## Notes
+
+- Relates to the earlier one-shot login redirect work (quick 260606-tv8) and the
+  OIDC state-cookie-churn fix (commit bb61d21 — gate events query on auth).
+- Verify with a real expiry (or shorten `OIDC_AUTH_EXPIRES` / Authelia
+  `refresh_token_lifespan` in a test) rather than only reasoning about it.