docs(ai): handoff state after frontend SSE slice lands

Marks the SSE subscription as shipped, points the next-session resume
target at the magic-moment handoff-context screen, and logs the live
end-to-end verification.

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

.ai/SESSION_LOG.md

@@ -12,6 +12,17 @@
 
 ---
 
+## 2026-04-27 21:00 EDT — Claude Code — Escalation Mode: frontend SSE subscription in EscalationQueue
+
+- Picked up `feat/escalation-metric-endpoint` after the Codex test-stabilization pass. Confirmed green starting state: focused backend subset `32 passed in 18.78s` with `-n auto`.
+- Implemented the live-arrival frontend slice. Added `streamEscalations(handlers, signal)` to `frontend/src/api/aiSessions.ts` — fetch-based `ReadableStream` reader (native `EventSource` can't send auth headers) that parses SSE frames (event/data/comment lines), buffers partial frames across chunks, ignores `: keepalive` heartbeats, dispatches `ready` and `handoff_created` events. Added `HandoffCreatedEvent` and `EscalationStreamHandlers` types in `frontend/src/types/ai-session.ts` mirroring the backend bus payload.
+- Rewrote `frontend/src/components/flowpilot/EscalationQueue.tsx`. SSE subscription with `AbortController` + exponential-backoff reconnect (1s → 30s cap, attempt counter resets on `ready`). On `handoff_created` the component refetches the queue, diffs against the previous IDs via a `sessionsRef`, prepends new arrivals (newest-first) above established cards (oldest-first preserved). New IDs are tagged for 800ms so the locked 200ms slide-in animation plays before cleanup. Tab-title flash: captures `document.title` at mount, prefixes `(N)` while `document.hidden`, clears on `focus` / `visibilitychange`, restores on unmount. `prefers-reduced-motion: reduce` swaps `animate-slide-in-bottom` for `animate-fade-in`. ARIA: `role="region"` + `aria-live="polite"` on the list, `aria-label="N escalations awaiting pickup"` on the heading; Pick Up button bumped to `py-2.5` to clear the 44px touch floor.
+- Verified end-to-end against the running dev stack. `tsc -b` exit 0. Vite HMR'd the new component without errors. Raw SSE handshake against `/api/v1/ai-sessions/escalations/stream` returned 200 with `text/event-stream; charset=utf-8` plus the locked headers (`cache-control: no-cache`, `x-accel-buffering: no`). Subscriber received the `ready` frame on connect; after posting a handoff via the API, the subscriber received the `handoff_created` frame with the full payload — wire format matches the parser exactly. Backend regression: same focused subset still `32 passed in 18.91s`.
+- Not yet verified (would need a real browser session): the slide-in animation visually plays, the tab title actually updates, the reduced-motion media-query path, AbortController cancellation on unmount, backoff after a real network blip. Wire contract is confirmed; these are visual/timing-dependent and follow from correct parser + state machine.
+- Smoke-test artifact: a single test handoff (`0f6149db…` on session `50ea20d4…`) is sitting in the engineer's queue from the verification step. Harmless; useful as visual demo data.
+- Left for next session: the magic-moment handoff-context screen — 4 sections (problem summary / what's been tried / AI assessment / Start here CTA), loads on Pick Up, dissolves into the regular FlowPilot session view. Must render gracefully when `ai_assessment` is `None` (per the 5s assessment timeout from Codex's earlier fix).
+- Files touched: `frontend/src/api/aiSessions.ts`, `frontend/src/types/ai-session.ts`, `frontend/src/components/flowpilot/EscalationQueue.tsx`, `.ai/CURRENT_TASK.md`, `.ai/HANDOFF.md`, `.ai/SESSION_LOG.md`.
+
 ## 2026-04-27 EDT — Claude Code — Escalation Mode wedge: design through SSE backend (8 commits)
 
 - One long session that produced the entire planning artifact stack and most of the backend for the Escalation Mode wedge. Output of `/office-hours` (8 founder-signal session, top-tier YC archetype indicators), `/plan-eng-review` (scope reduced from "2-3 weeks greenfield" to "~6-9 days integration + metric + polish" once the existing handoff_manager surface was inventoried), `/plan-design-review` (6/10 → 9/10 with magic-moment screen, hero metric placement, and real-time arrival visual locked), and `/codex review` (12 findings, 6 applied — two-metric framing, notification routing, claim auth gate moved in-scope, unread-state fix, "Start here" CTA reframe, per-channel delivery model; 5 rejected including the full-scope reduction Codex pushed for).