feat(pilot): Phase 3 — Suggested fix tracking + Resolve preview with state_version cache

Adds the AI-proposed resolution path and the inline preview of the
markdown that will be posted to the customer ticket on Resolve. The
preview is keyed on (session_id, ai_sessions.state_version) so back-to-
back fetches against unchanged state hit an in-process cache instead
of paying for a Sonnet call.

Backend:
- preview_cache: in-process LRU keyed on (kind, session_id, state_version).
  No TTL — state_version is the source of truth. Soft-cap 5000 entries.
- unified_chat_service: [SUGGEST_FIX] parser (last-block-wins, JSON
  payload, confidence clamped 0-100), supersession persistence (sets
  superseded_at on prior active row), atomic state_version bump.
- ResolutionNoteGeneratorService: pulls session, facts, active fix, and
  redacted script_generations into a structured input bundle for Sonnet;
  produces the four-section markdown (Problem / What we confirmed /
  Root cause / Resolution). Sensitive script parameters redacted via
  ScriptTemplateEngine.redact_sensitive driven by the template's
  parameters_schema.
- /api/v1/ai-sessions/{id}/suggested-fixes/active — 200 with the active
  fix or 404.
- /api/v1/ai-sessions/{id}/suggested-fixes/{fix_id}/decision — records
  one_off / draft_template / build_template / dismissed; dismiss
  supersedes; bumps state_version. 409 on dismissing an already-
  superseded fix.
- /api/v1/ai-sessions/{id}/resolution-note/preview — generates or returns
  cached markdown; from_cache flag in payload signals cache hit.
- scripts.py POST /generate now bumps state_version on the linked
  ai_session_id when present (third source of preview-cache invalidation
  per Section 5.5).
- ASSISTANT_SYSTEM_PROMPT documents [SUGGEST_FIX] (when to/not to emit,
  format, supersession semantics).
- 12 tests covering the parser (well-formed, last-wins, malformed,
  confidence clamping), supersession + state_version invariant, all
  decision branches, preview cache hit-on-no-change + miss-after-write.

Frontend:
- src/components/pilot/sections/SuggestedFix.tsx — amber-accented card
  with confidence badge; dismiss action wired to the decision endpoint.
- src/components/pilot/ResolutionNotePreview.tsx — popover with refresh,
  loading state, cached/fresh indicator, ticket-ref display.
- src/api/sessionSuggestedFixes.ts — typed client; getActive normalizes
  404 to null so callers don't have to special-case.
- TaskLane gains suggestedFixSlot + bottomSlot props (rendered after
  Diagnostic Checks; bottomSlot anchors the Resolve action).
- AssistantChatPage: refreshSessionDerived helper batches fact + fix
  refresh; fact mutations and chat sends both schedule a 500ms-debounced
  preview refresh per the Section 5.5 spec.

Verified end-to-end against the dev stack with a real Sonnet call:
- /active 404 → fact create → preview generates four-section markdown
  grounded only in provided facts → second preview call hits cache
  (from_cache=true, no LLM call) → fact write 2 → cache miss, regenerates.

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

frontend/src/components/assistant/TaskLane.tsx

@@ -43,6 +43,12 @@ interface TaskLaneProps {
   // shape lets the parent own fact-fetching and state-version polling without
   // pulling that concern into TaskLane.
   whatWeKnowSlot?: React.ReactNode
+  // Phase 3: Suggested fix card, rendered below Diagnostic Checks.
+  suggestedFixSlot?: React.ReactNode
+  // Phase 3: bottom-of-lane slot for the Resolve action bar + preview popover
+  // (parent owns state). Renders inside the scrollable body so the popover
+  // stays anchored as the lane scrolls.
+  bottomSlot?: React.ReactNode
 }
 
 // ── Storage helpers ──
@@ -69,7 +75,7 @@ export function clearTaskState(sessionId: string) {
 
 // ── Component ──
 
-export function TaskLane({ questions, actions, sessionId, onSubmit, onClose, loading, whatWeKnowSlot }: TaskLaneProps) {
+export function TaskLane({ questions, actions, sessionId, onSubmit, onClose, loading, whatWeKnowSlot, suggestedFixSlot, bottomSlot }: TaskLaneProps) {
   const [tasks, setTasks] = useState<TaskResponse[]>(() => {
     // Try to restore saved state for this session (preserves user's in-progress answers)
     if (sessionId) {
@@ -503,6 +509,12 @@ export function TaskLane({ questions, actions, sessionId, onSubmit, onClose, loa
             })}
           </section>
         )}
+
+        {/* ── Suggested fix (Phase 3) ── */}
+        {suggestedFixSlot}
+
+        {/* ── Resolve action bar + preview popover (Phase 3) ── */}
+        {bottomSlot}
       </div>
 
       {/* Footer */}