webclient: Backgrounds tab in artifacts panel + task toasts ...

- new Backgrounds tab: task list (running first, badges, per-tool icons)
  with a detail view (status, timestamps, sub-agent tokens, result/progress)
- GET /sessions/{id}/tasks snapshot endpoint: task_update events are not
  replayed on reconnect, so the client fetches the task list on session
  load/reload; live task_update entries are merged on top (chat.fetchTasks)
- terminal task_update no longer removes the entry — it marks it finished
  so the tab shows recent completions; _terminalTaskIds still blocks
  resurrection by a late running update
- toasts for background task start / finish (info / success / error) in
  the WS dispatch; silent for other sessions and unknown terminal ids
- persistent background-tasks chip removed (replaced by the tab); only
  the queued-messages chip stays
- fix invisible status text in terminal detail rows: filled .status-*
  backgrounds now scope to .terminal-status-badge only

background tasks: review fixes B1-B11 batch ...

- stop mid-batch cancels in-flight tools (B1) and keeps real results
  of already-finished ones, mixing them with synthetic stopped notes
  in call order (B2)
- queued messages: headless drain publishes session_sync (B4), the
  run's teardown broadcasts session_sync to other sockets but not the
  owner socket (prevents double reload) (B5)
- task_update notifications are chained per task so late running
  updates can't overtake the terminal one (B7; client drops late
  re-flicker of a terminal task chip) (B8)
- client: ui_component results reference the owning message via
  card.parentMsg instead of a stale msg reference (B6)
- tasks cancel reports the real outcome after a bounded wait instead
  of an optimistic 'cancelled' (B9)
- session delete cancels its running background jobs and drops
  pending result notes (B10)
- subagent tool loop routes background:true calls through
  ToolExecutor._maybe_background like the main loop (B11)
- tests for all of the above; docs/tasks.md stop/cancel semantics

webclient: virtualized message list (DynamicScroller) ...

- MessageList rewritten on vue-virtual-scroller DynamicScroller; only rows
  near the viewport mount (session switch 650-730ms longtask / DOM 31645 ->
  110-165ms / DOM 1-2.5k, zero freezes)
- scroller is keyed by session id: message ids repeat across sessions, so
  teardown drops the measured-size cache on switch
- convergeToBottom watches the bottom hold for a bounded window after
  landing (lazy row measurements nudge scrollHeight late); yields to wheel/
  pointer/touch input instead of scroll-position heuristics, which the
  scroller's own adjustments would trip
- renderMarkdown gets a byte-capped LRU memo so markdown remount cost is
  amortized while virtualized rows recycle
- removed dead .message-list/.message-list-inner styles

webclient: loading indicators where the UI looked frozen ...

- session open: centered spinner in MessageList while chat.loading
- image paste/drop: imagesProcessing counter (chat store, shared);
  FilePreviewStrip shows spinner placeholder tiles where the resized
  previews will land
- file upload: indeterminate sliding bar instead of the fake static 60%
- send → run start gap: "Sending…" hint with spinner, cleared on
  stream_start / message_queued / stream end / error / session switch
- content-card images: skeleton with spinner until @load (reset on src
  change); wrapper keeps min-height while the img is empty

vitest 96 passed.

chat history pagination: paged load instead of full-session fetch ...

Backend:
- PgSessionStore.get_meta — light session head (sessions row + COUNT),
  no message payload
- PgSessionStore.get_history_page — page of display history (archive ∪
  hot UNION), newest-first page, oldest-first result, limit+1 peek for
  has_more; each message stamped metadata.display_index (ROW_NUMBER-1
  over the full display history) so client ids stay stable across
  paged loads; dangling-tool-call repair keeps real ranks by
  sequence-number lookup
- GET /sessions/{id}/meta and GET /sessions/{id}/messages/history
  (before_seq cursor, limit ≤200)

Webclient:
- loadSession/reloadSession fetch meta + newest 200-item page
  (Promise.all), archive state from the page itself
- buildMessageList ids (h_*) and rawIndices use the global
  display_index — feedback keys and search-jump stay stable when
  history is paged
- scroll-up loads older pages through the same history endpoint
  (archive table alone misses sessions whose threshold never moved)
- search-jump pulls pages until the target index is covered (bounded)

Tests: store unit tests (ranks, has_more peek, placeholder shift) +
vitest updates; full pytest 1231 passed, vitest 94 passed.

webclient: background task chip, id-first tool matching, queued badge ...

- toolIndex (tool_call_id → card): exact matching for parallel batches and
  late events after stream_end; legacy name+pending fallback kept
- bare tool_call synthesizes a card so results are never lost
- task_update: backgroundTasks chip above composer + steps appended to the
  spawning tool card (parent_tool_call_id binding)
- message_queued badge, terminal_opened dispatch
- new BackgroundTasksChip component, task_update step rendering in ToolCard

webclient: lightbox dialog shrink-wraps the photo, img without crop

webclient: code blocks span full message width in flex markdown container

PWA: installable webclient, offline shell, web push ...

Installability:
- public/manifest.webmanifest (standalone, theme #16161E) + PNG icons
  generated from logo.svg (regular + maskable, served via /images mount)
- index.html: manifest link, theme-color, apple-touch-icon

Offline shell:
- hand-rolled sw.js (no workbox): navigation = network-first (3s race)
  with cached-shell fallback + background refresh (a stale cached shell
  would 404 on entry chunks after a deploy); /assets/* cache-first
  (content-hashed); /images/* cache-first capped; /api,/ws,/auth,/push,
  /content pass-through
- vite closeBundle plugin stamps __NAVI_BUILD_VERSION__ (digest of
  index.html + asset names) into dist/sw.js; sw.js served no-store so
  every deploy reactivates the SW and activation evicts old caches
- SW registration in main.js, PROD only (dev HMR untouched)
- OfflineBanner (useOnline composable) over the app shell

Web push (VAPID, pywebpush):
- navi/push/ package: push_subscriptions table (postgres, boot-time DDL),
  PushSubscriptionStore, PushService (async fan-out, to_thread sends,
  404/410 prunes dead endpoints, per-session cooldown)
- routes: GET /push/vapid-key, POST/DELETE /push/subscribe (auth-gated)
- trigger in orchestrator run_agent + run_recall: push on StreamEnd when
  no WebSocket client watches the session; fire-and-forget, never
  disturbs the run; anonymous fallback only when auth is off
- client: usePush composable + Notifications settings panel (enable/
  disable via PushManager.subscribe with the server VAPID key)
- notification click focuses the app at /#<session_id> (hash routing
  opens the right chat); payload body is a markdown-stripped <=140-char
  preview

NAVIVAPID keys empty = push fully disabled (graceful, like other optional
integrations). dist/ artifacts committed per repo convention.

Tests: pytest push store/service/routes/trigger (+23), vitest usePush
(83 webclient tests green). Full suite 1143 passed.