The lightbox is now one dialog for every file the artifacts panel and the
content cards can show: audio and video players on the kit's own controls, a
text/source view with highlight.js, and a three.js viewer that replaced the
standalone stl.html frame with a model one. highlight.js emits .hljs-* classes
and ships no theme, so until now every highlighted block rendered in one flat
colour — app.scss now carries the palette.

While a turn runs, the send button no longer turns into Stop and vanishes the
draft with it: the message goes into the socket and is marked "queued" until
the stream_start of the turn that consumes it, the write-now-run-next model
navi-code uses. Send and Stop sit side by side, and the queue chip takes the
larger of the local and the server's counts.

The socket keeps its own liveness: a ping every 20 s, a watchdog that reopens a
socket silent for 45 s or stuck in CONNECTING, and a reconnect on resume from
background, network return or bfcache. On reopen it drops a half-written
message left by the dead socket, so the session_sync that follows is not hidden
behind a stream that will never finish.

- 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

- 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

Backend:
- auth/deps: fix refresh-lock clock race (cleanup now monotonic like the cache)
- core/registry: add missing structlog logger (NameError on fallback path)
- config: GNAUTH_WEBHOOK_SECRET, NAVI_ALLOWED_ORIGINS (+list property)
- webhooks: HMAC-SHA256 signature verification (503 unconfigured in auth mode,
  unsigned+warning in no-auth mode, 403 bad/stale signature, 400 bad JSON)
- main: CORS from NAVI_ALLOWED_ORIGINS in auth mode (fail-fast on empty),
  eval router behind require_admin, /debug only registered in no-auth mode
- auth routes: mobile-done sid validation (32 hex) + CSP header + safe JS
  escaping (reflected XSS); Secure cookie flag via helper (https base URL)
- websocket: anonymous WS rejected in auth mode (closes legacy-session RCE);
  socket registered only after access checks; stop_session auth gate
- messages: REST agent start now takes session lock + busy flag (409 on
  active run), contextvars reset in finally

Webclient:
- useMarkdown: DOMPurify.sanitize on all rendered markdown (stored XSS),
  image-URL scheme whitelist, delegated error listener (no inline onerror)
- html.html artifact viewer: sandbox without allow-same-origin (opaque origin)
- tests: DOMPurify runs under jsdom (happy-dom Node.prototype.nodeName getter
  breaks DOMPurify); useWebSocket tests get localStorage stub + ui-kit alias

Tests: pytest 1049 passed, 1 skipped; vitest 61 passed

- Vitest + @vue/test-utils + happy-dom setup
- api/index.test.js: 8 tests for fetch wrapper, verbs, errors, FormData
- stores/chat.test.js: 23 tests for buildMessageList, WS handlers, load/clear
- stores/sessions.test.js: 6 tests for fetch, create, delete, pin, preview
- stores/profiles.test.js: 3 tests for fetch, auto-select, lookup
- composables/useWebSocket.test.js: 7 tests with MockWebSocket
- Export buildMessageList from chat store so tests can verify message parsing
- Update docs/testing.md with webclient stack, layout, and commands

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>