feat(pilot): Phase 4 — Resolve + Escalate PSA writebacks with status verification

Wires the preview popover's Confirm & post action to ConnectWise (and,
via the provider pattern, any future PSA). Adds the parallel Escalate
flow with the handoff-oriented five-section markdown. Sessions without a
linked PSA ticket resolve/escalate locally — markdown stored, status
flipped, nothing posted externally.

Backend:
- EscalationPackageGeneratorService: Sonnet, five sections (Problem /
  What we've confirmed / What we've tried / Current hypothesis /
  Suggested next steps). Shares the preview_cache with a separate KIND
  so Resolve and Escalate previews for the same state coexist.
- PSAWritebackService: post_resolution_note (RESOLUTION note type,
  customer-visible), post_escalation_package (INTERNAL_ANALYSIS,
  handoff for the next engineer only), transition_ticket_status with
  mandatory re-fetch verification. PSAStatusVerificationError surfaces
  loudly when CW silently rejects a status change — the
  ConnectWise anti-pattern CLAUDE.md flags.
- Endpoints:
  * POST /ai-sessions/{id}/escalation-package/preview
  * POST /ai-sessions/{id}/resolution-note/post
  * POST /ai-sessions/{id}/escalation-package/post
  Outcomes: "resolved" / "escalated" with external_id + verified status,
  "resolved_local" / "escalated_local" when no PSA linked.
- Target CW status IDs live in account_settings.preferences
  (cw_resolved_status_id, cw_escalated_status_id). When unset, the post
  proceeds without a status transition — response includes a
  status_transition_skipped_reason rather than silently erroring.
- 7 tests: local-only path, PSA happy path with verified transition,
  status verification failure → 502, skipped transition when
  unconfigured, 409 on already-resolved re-post, escalate parallel path,
  internal-analysis note type enforced.

Frontend:
- ResolutionNotePreview now kind-parameterized ('resolve' | 'escalate')
  with inline edit + Confirm & post. Preview loads from the matching
  backend endpoint; posting calls the matching endpoint; outcome toast
  surfaces the verified CW status or the local-only result.
- AssistantChatPage: previewKind state replaces previewOpen; two toggle
  buttons (Preview Resolve note / Escalate instead) in the lane's bottom
  slot. handleConfirmPost dispatches by kind.

Verified 2026-04-22:
- Local-only Resolve + Escalate round-trip against the dev stack.
- Live Sonnet escalation-package preview; cache hit on repeat call
  with no state change (separate cache kind from resolution-note).
- PSA post + status-verification paths covered by mocked-provider pytest
  cases. Live CW round-trip pending a test CW instance.

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

frontend/src/api/sessionSuggestedFixes.ts

@@ -36,6 +36,16 @@ export interface ResolutionNotePreview {
   from_cache: boolean
 }
 
+export interface ResolutionPostResponse {
+  outcome: 'resolved' | 'escalated' | 'resolved_local' | 'escalated_local'
+  session_status: string
+  external_id: string | null
+  posted_at: string | null
+  verified_status_id: number | null
+  verified_status_name: string | null
+  status_transition_skipped_reason: string | null
+}
+
 export const sessionSuggestedFixesApi = {
   /**
    * Returns the active suggested fix for a session, or `null` if there isn't one.
@@ -79,6 +89,45 @@ export const sessionSuggestedFixesApi = {
     )
     return r.data
   },
+
+  /**
+   * Parallel to getResolutionNotePreview, for the Escalate flow (five-section
+   * handoff markdown). Separate backend cache kind, same state_version invariant.
+   */
+  async getEscalationPackagePreview(sessionId: string): Promise<ResolutionNotePreview> {
+    const r = await apiClient.post<ResolutionNotePreview>(
+      `/ai-sessions/${sessionId}/escalation-package/preview`,
+    )
+    return r.data
+  },
+
+  /**
+   * Post the engineer-edited resolution markdown to PSA + mark session resolved.
+   * Local-only when the session has no linked PSA ticket (outcome = "resolved_local").
+   */
+  async postResolutionNote(
+    sessionId: string,
+    markdown: string,
+    resolutionSummary?: string,
+  ): Promise<ResolutionPostResponse> {
+    const r = await apiClient.post<ResolutionPostResponse>(
+      `/ai-sessions/${sessionId}/resolution-note/post`,
+      { markdown, resolution_summary: resolutionSummary },
+    )
+    return r.data
+  },
+
+  async postEscalationPackage(
+    sessionId: string,
+    markdown: string,
+    escalationReason?: string,
+  ): Promise<ResolutionPostResponse> {
+    const r = await apiClient.post<ResolutionPostResponse>(
+      `/ai-sessions/${sessionId}/escalation-package/post`,
+      { markdown, escalation_reason: escalationReason },
+    )
+    return r.data
+  },
 }
 
 export default sessionSuggestedFixesApi