v0.23.0: server-side sign-in state resume (roadmap #29)

Track each authenticated user's last-viewed route + light view state
server-side, and on next sign-in redirect them to that state, falling
back to the empty-state home only when there's no recorded state.

Backend:
- migration 022_user_session_state.sql: one row per user
  (user_id PK/FK, last_route, last_route_state JSON-as-TEXT,
  resume_enabled default 1, last_updated_at).
- PUT /api/me/last-state (require_user): upserts route + light state;
  no-ops when resume_enabled=0. Localized in the /me region.
- /api/auth/me payload now carries resume_enabled + last_route +
  decoded last_route_state (no extra round-trip).
- test_session_resume_vertical.py: auth-required, upsert/read-back,
  per-user isolation, resume_enabled=0 disable.

Frontend:
- lib/useLastState.js: debounced (~1s) route-change PUT for
  authenticated users; one-time resume redirect on sign-in, gated on
  identify having fired (preserves #21 Part C identify-then-track).
- api.js: putLastState() client call.
- App.jsx: import + call the hook; set identifyReady after identify.
  Header region untouched.

Per-user (not per-device); profile-settings opt-out toggle UI
deferred (column + default-on behavior ship now). Stored state is
route + light view state ONLY, never draft buffers — documented in
SPEC §6.8.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/App.jsx

@@ -2,6 +2,7 @@ import { useEffect, useRef, useState } from 'react'
 import { Routes, Route, Link, Navigate, useLocation, useNavigate } from 'react-router-dom'
 import { getMe, subscribeToNotifications } from './api'
 import { anonymize, EVENTS, identify, track } from './lib/analytics'
+import { useLastState } from './lib/useLastState'
 import Catalog from './components/Catalog.jsx'
 import Inbox from './components/Inbox.jsx'
 import RFCView from './components/RFCView.jsx'
@@ -42,6 +43,12 @@ export default function App() {
   // "Privacy & cookies" tab dispatches a `rfc-app:cookie-consent-reopen`
   // event that bumps this.
   const [consentReopenTick, setConsentReopenTick] = useState(0)
+  // v0.23.0 / item #29 — flips true once the #21-Part-C identify effect
+  // has fired (or once we've confirmed there's no authenticated user to
+  // identify). useLastState gates its resume redirect on this so the
+  // redirect always happens AFTER identify, preserving identify-then-
+  // track ordering.
+  const [identifyReady, setIdentifyReady] = useState(false)
   const navigate = useNavigate()
   const location = useLocation()
   // v0.15.0 — Page Viewed event taxonomy. We fire on every
@@ -86,6 +93,9 @@ export default function App() {
       if (viewer?.first_sign_in_at) props.first_sign_in_at = ['__setOnce__', viewer.first_sign_in_at]
       if (viewer?.created_at) props.account_created_at = ['__setOnce__', viewer.created_at]
       identify({ user_id: String(uid), properties: props })
+      // v0.23.0 / item #29 — identify has now fired for this sign-in;
+      // release useLastState's resume redirect (it waits on this).
+      setIdentifyReady(true)
     } else if (uid == null && lastUserIdRef.current != null) {
       // Sign-out edge — App-level reset is handled separately by the
       // sign-out gesture that fires User Signed Out. Clear our local
@@ -94,6 +104,14 @@ export default function App() {
     }
   }, [me?.authenticated, me?.user?.id, me?.user?.role, me?.user?.permission_state, me?.user?.passcode_set, me?.user?.device_trusted])
 
+  // v0.23.0 / item #29 — once `me` has resolved, if there's no
+  // authenticated user there is nothing to identify, so release the
+  // resume gate immediately (anonymous boots have no resume to do, but
+  // the hook still needs the gate resolved to be a clean no-op).
+  useEffect(() => {
+    if (me != null && !me.authenticated) setIdentifyReady(true)
+  }, [me])
+
   useEffect(() => {
     const handler = () => setConsentReopenTick(t => t + 1)
     window.addEventListener('rfc-app:cookie-consent-reopen', handler)
@@ -107,6 +125,18 @@ export default function App() {
       .finally(() => setLoading(false))
   }, [])
 
+  // v0.23.0 / item #29 — server-side sign-in state resume. The hook
+  // debounce-posts the current route for authenticated users and, once
+  // identify has fired, redirects a fresh sign-in (which hard-lands on
+  // "/") to the user's stored last route. Anonymous users: no-op.
+  useLastState({
+    authenticated: !!me?.authenticated,
+    pathname: location.pathname,
+    identifyReady,
+    lastRoute: me?.authenticated ? me.user?.last_route : null,
+    navigate,
+  })
+
   // §15.3 — subscribe to the live SSE stream for authenticated viewers
   // so the badge counter and the toast surface stay in lockstep with
   // the inbox. Tabs that miss an event because they were closed pick