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: session-list polish from review pass ...

- documentTitle: persistent nameById map — names for sessions beyond the
  loaded list page (list only holds ~30); map filled by fetches and
  loadSession meta, never wiped by later refetches
- createSession: placeholder inserted at the position the server list
  would give it (after pinned run, last_active desc) so refetch no
  longer visibly moves the new row
- SessionItem: skip empty .session-icons wrapper when no icons
- drawer breakpoint made exclusive (-sidebar-drawer 1280 -> 1279.98):
  viewport of exactly 1280px now gets the desktop sidebar

webclient: fix session-list flicker and double-load on select ...

- fetchSessions merges into existing items (preserve object references)
  instead of wholesale array replacement — DynamicScroller reuses rows,
  the list no longer repaints/reflows on every refetch (measured: sidebar
  repaint spikes 8-17% per switch -> 0)
- AppSidebar.handleSelect no longer refetches the list on a plain select;
  refetch only when leaving search (the array still held search results)
- loadSession now lives only in handleSelect — SessionList.onSelect used
  to start a first load and handleSelect raced it with a second one
  (double fetch + double buildMessageList, incl. search-jump target)
- pinSession mutates in place instead of replacing every item object
- SessionItem.highlightText matches on the raw string so <mark> offsets
  stay correct when the text contains &/</>

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

Add session search across messages with backend + frontend ...

Backend:
- GET /sessions now accepts `search` query param
- _session_summary computes match_indices and match_preview from messages
- pg_session_store: messages ILIKE added to search_list and count_all
- In-memory store: search_list also filters by message content

Frontend:
- AppSidebar: search toggle icon + debounced input, Ctrl+K shortcut
- SessionItem: highlight matching text, show match_preview from search
- SessionList: pass searchQuery to SessionItem
- SessionsStore: searchQuery/searchActive state, setSearch/clearSearch
- API layer: getSessions accepts search param
- MessageList: scroll to target message + brightness flash animation
- ChatStore: loadSession accepts targetMessageIndex, scrollToMessageIndex ref
- CSS: msg-flash keyframe animation in app.scss
- Tests updated for new getSessions signature

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

Paginate session list loading

Refine 3D modeler workflow

Add webclient unit tests (Vitest) — 47 tests ...

- 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>