feat(pilot): Phase 2 — What we know (facts) with stable task-lane IDs

Adds the load-bearing structural feature of the FlowPilot migration: a
"What we know" panel that holds confirmed facts for a session, fed by AI
[PROMOTE] markers and engineer-added notes. Facts feed the resolution
note preview (Phase 3) and survive across turns via stable UUIDs assigned
to pending_task_lane items.

Backend:
- FactSynthesisService: create/update/soft-delete facts with atomic
  state_version bumps; LLM-backed synthesize_from_question/check on the
  fact_synthesis (Haiku) action tier per Section 6.6.
- /api/v1/ai-sessions/{id}/facts CRUD + /facts/promote (proposed_text or
  via synthesis). PATCH returns 403 for question/diagnostic_check facts
  (edit the source item instead, Section 7.3).
- unified_chat_service: [PROMOTE] marker parser (JSON-block per Section
  8.1 spec drift note), stable-UUID assignment for pending_task_lane
  questions/actions preserved by exact text/label match across turns.
- ASSISTANT_SYSTEM_PROMPT: documents [PROMOTE] format, when to/not to
  emit, hallucination guardrails, source_ref handling.
- 17 tests covering parser, stable IDs, service validation, CRUD,
  editability rule, both promote modes, 422 null-synthesis path,
  state_version invariant.

Frontend:
- src/components/pilot/sections/{WhatWeKnow,WhatWeKnowItem,AddNoteButton}
  — green-gradient section above Questions, dashed-circle check, inline
  edit/delete gated by the server's editable flag.
- TaskLane gains a whatWeKnowSlot prop (existing assistant/ folder kept
  per the doc's "rename is opportunistic" guidance).
- AssistantChatPage fetches facts on selectChat and refetches after each
  chat send (so [PROMOTE]-synthesized facts appear immediately); auto-
  opens the lane when facts exist.

Verification: end-to-end smoke against the local docker stack confirms
all five endpoints (list/create/patch/delete/promote) plus the 403
editability rule. pytest suite verifies the same with mocked LLM. Live
[PROMOTE] flow remains untested until used in the UI — the marker shape
is covered by parser tests.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/assistant/TaskLane.tsx

@@ -38,6 +38,11 @@ interface TaskLaneProps {
   onSubmit: (responses: TaskResponse[]) => void
   onClose: () => void
   loading?: boolean
+  // Slot for the FlowPilot Phase 2 "What we know" section. Rendered above
+  // Questions in the body (per FLOWPILOT-MIGRATION.md Section 3.1). The slot
+  // shape lets the parent own fact-fetching and state-version polling without
+  // pulling that concern into TaskLane.
+  whatWeKnowSlot?: React.ReactNode
 }
 
 // ── Storage helpers ──
@@ -64,7 +69,7 @@ export function clearTaskState(sessionId: string) {
 
 // ── Component ──
 
-export function TaskLane({ questions, actions, sessionId, onSubmit, onClose, loading }: TaskLaneProps) {
+export function TaskLane({ questions, actions, sessionId, onSubmit, onClose, loading, whatWeKnowSlot }: TaskLaneProps) {
   const [tasks, setTasks] = useState<TaskResponse[]>(() => {
     // Try to restore saved state for this session (preserves user's in-progress answers)
     if (sessionId) {
@@ -269,6 +274,9 @@ export function TaskLane({ questions, actions, sessionId, onSubmit, onClose, loa
       {/* Body */}
       <div className="flex-1 overflow-y-auto p-3 space-y-4">
 
+        {/* ── What we know (Phase 2) ── */}
+        {whatWeKnowSlot}
+
         {/* ── Questions Section ── */}
         {questionTasks.length > 0 && (
           <section>