feat(escalations): subscribe EscalationQueue to live SSE arrivals

Adds the frontend live-arrival slice on top of the test-stabilized SSE
backend. Senior techs now see a junior's escalation slide into the
queue without refresh.

- streamEscalations(handlers, signal) in aiSessions.ts: fetch-based
  ReadableStream parser (native EventSource cannot send auth headers).
  Handles SSE frames, partial frames across chunks, : keepalive
  heartbeats. Dispatches ready and handoff_created.
- HandoffCreatedEvent + EscalationStreamHandlers types mirror the bus
  payload published by HandoffManager.dispatch_escalation_notifications.
- EscalationQueue.tsx: AbortController-managed subscription with
  exponential-backoff reconnect (1s → 30s cap, attempt counter resets
  on ready). On handoff_created, refetch and diff against previous IDs
  via sessionsRef; new arrivals prepended (newest-first) above
  established cards (oldest-first preserved). Slide-in tag held for
  800ms so the locked 200ms animation completes. Tab-title flash
  prefixes (N) while document.hidden, restores on focus / unmount.
  prefers-reduced-motion swaps slide-in for fade-in. ARIA region +
  aria-live=polite + aria-label on heading. Pick Up bumped to py-2.5
  to clear the 44px touch floor.

Verified end-to-end against the running dev stack: subscriber received
the ready frame on connect; after posting a handoff via the API, the
subscriber received the handoff_created frame with the expected
payload — wire format matches the parser. Backend regression: focused
subset still 32 passed in 18.91s. Frontend tsc -b clean.

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

frontend/src/api/aiSessions.ts

@@ -18,6 +18,8 @@ import type {
   ChatSessionCreateResponse,
   ChatMessageRequest,
   ChatMessageResponse,
+  HandoffCreatedEvent,
+  EscalationStreamHandlers,
 } from '@/types/ai-session'
 
 export const aiSessionsApi = {
@@ -220,6 +222,73 @@ export const aiSessionsApi = {
     return response.data
   },
 
+  // Native EventSource cannot send Authorization headers, so we use fetch +
+  // ReadableStream and parse SSE frames manually (same pattern as
+  // `streamDocumentation`). The returned promise resolves on clean stream
+  // close (server hangs up) and rejects on network/HTTP error so the caller
+  // can decide whether to reconnect with backoff.
+  async streamEscalations(
+    handlers: EscalationStreamHandlers,
+    signal: AbortSignal,
+  ): Promise<void> {
+    const token = localStorage.getItem('access_token')
+    const baseUrl = import.meta.env.VITE_API_URL || ''
+
+    const response = await fetch(
+      `${baseUrl}/api/v1/ai-sessions/escalations/stream`,
+      {
+        headers: { Authorization: `Bearer ${token}` },
+        signal,
+      },
+    )
+
+    if (!response.ok) {
+      throw new Error(`Escalation stream failed: HTTP ${response.status}`)
+    }
+
+    const reader = response.body?.getReader()
+    if (!reader) {
+      throw new Error('Escalation stream: no response body')
+    }
+
+    const decoder = new TextDecoder()
+    let buffer = ''
+
+    while (true) {
+      const { done, value } = await reader.read()
+      if (done) return
+
+      buffer += decoder.decode(value, { stream: true })
+
+      // SSE frames are separated by blank lines. Hold the trailing partial
+      // frame in the buffer until the next chunk completes it.
+      const frames = buffer.split('\n\n')
+      buffer = frames.pop() ?? ''
+
+      for (const frame of frames) {
+        if (!frame) continue
+        let eventType = 'message'
+        let data = ''
+        for (const line of frame.split('\n')) {
+          if (line.startsWith(':')) continue // comment / keepalive
+          if (line.startsWith('event: ')) eventType = line.slice(7).trim()
+          else if (line.startsWith('data: ')) data += line.slice(6)
+        }
+        if (!data) continue
+        try {
+          const parsed = JSON.parse(data) as Record<string, unknown>
+          if (eventType === 'handoff_created' && parsed.type === 'handoff_created') {
+            handlers.onHandoffCreated?.(parsed as unknown as HandoffCreatedEvent)
+          } else if (eventType === 'ready') {
+            handlers.onReady?.()
+          }
+        } catch {
+          // skip malformed frame
+        }
+      }
+    }
+  },
+
   async search(q: string, limit: number = 5): Promise<AISessionSearchResult[]> {
     const response = await apiClient.get<AISessionSearchResult[]>('/ai-sessions/search', {
       params: { q, limit },

frontend/src/components/flowpilot/EscalationQueue.tsx

@@ -1,15 +1,31 @@
-import { useState, useEffect } from 'react'
+import { useCallback, useEffect, useMemo, useRef, useState } from 'react'
 import { useNavigate } from 'react-router-dom'
 import { AlertTriangle, Clock, Hash, Ticket, Loader2, RefreshCw } from 'lucide-react'
 import { aiSessionsApi } from '@/api'
 import type { AISessionSummary } from '@/types/ai-session'
 import { timeAgo } from '@/lib/timeAgo'
+import { cn } from '@/lib/utils'
 
 interface EscalationQueueProps {
   onPickup?: (sessionId: string) => void
   onCountChange?: (count: number) => void
 }
 
+// Static list sort: oldest-first. Longest waiting = most urgent.
+const sortOldestFirst = (a: AISessionSummary, b: AISessionSummary) =>
+  new Date(a.created_at).getTime() - new Date(b.created_at).getTime()
+
+// Live-arrival bucket sort: newest-first so the most recent escalation is at
+// the very top of the list.
+const sortNewestFirst = (a: AISessionSummary, b: AISessionSummary) =>
+  new Date(b.created_at).getTime() - new Date(a.created_at).getTime()
+
+// How long a freshly-arrived card keeps the slide-in animation class. The
+// keyframe itself runs 200ms; this just keeps the class on the DOM long
+// enough for the animation to finish before React removes it on the next
+// state transition.
+const NEW_CARD_HIGHLIGHT_MS = 800
+
 function waitTimeColor(createdAt: string): string {
   const hours = (Date.now() - new Date(createdAt).getTime()) / 3_600_000
   if (hours >= 4) return '#f87171'   // danger
@@ -22,29 +38,156 @@ export function EscalationQueue({ onPickup, onCountChange }: EscalationQueueProp
   const [sessions, setSessions] = useState<AISessionSummary[]>([])
   const [isLoading, setIsLoading] = useState(true)
   const [error, setError] = useState<string | null>(null)
+  // Session IDs that arrived via SSE and should still play the slide-in.
+  const [newIds, setNewIds] = useState<Set<string>>(new Set())
+  // Track count of unseen arrivals while the tab is backgrounded.
+  const [unseenCount, setUnseenCount] = useState(0)
 
-  const loadQueue = async () => {
+  // Ref mirrors the latest sessions so the SSE handler can diff without
+  // re-binding on every state change.
+  const sessionsRef = useRef<AISessionSummary[]>([])
+  useEffect(() => {
+    sessionsRef.current = sessions
+  }, [sessions])
+
+  const prefersReducedMotion = useMemo(() => {
+    if (typeof window === 'undefined' || !window.matchMedia) return false
+    return window.matchMedia('(prefers-reduced-motion: reduce)').matches
+  }, [])
+
+  // ── Tab title flash ──
+  // Capture the original title once at mount. While unseen > 0, prefix it.
+  const originalTitleRef = useRef<string>('')
+  useEffect(() => {
+    originalTitleRef.current = document.title
+    return () => {
+      // Restore on unmount so a leftover "(N) ..." prefix doesn't bleed
+      // into the next page.
+      document.title = originalTitleRef.current
+    }
+  }, [])
+
+  useEffect(() => {
+    const base = originalTitleRef.current || document.title
+    document.title = unseenCount > 0 ? `(${unseenCount}) ${base}` : base
+  }, [unseenCount])
+
+  useEffect(() => {
+    const clearUnseen = () => {
+      if (!document.hidden) setUnseenCount(0)
+    }
+    const onFocus = () => setUnseenCount(0)
+    document.addEventListener('visibilitychange', clearUnseen)
+    window.addEventListener('focus', onFocus)
+    return () => {
+      document.removeEventListener('visibilitychange', clearUnseen)
+      window.removeEventListener('focus', onFocus)
+    }
+  }, [])
+
+  const loadQueue = useCallback(async () => {
     setIsLoading(true)
     setError(null)
     try {
       const data = await aiSessionsApi.getEscalationQueue()
-      // Sort oldest-first — longest waiting = most urgent
-      const sorted = [...data].sort(
-        (a, b) => new Date(a.created_at).getTime() - new Date(b.created_at).getTime()
-      )
+      const sorted = [...data].sort(sortOldestFirst)
       setSessions(sorted)
+      setNewIds(new Set())
       onCountChange?.(sorted.length)
     } catch {
       setError('Failed to load escalation queue')
     } finally {
       setIsLoading(false)
     }
-  }
+  }, [onCountChange])
 
   useEffect(() => {
     loadQueue()
-    // eslint-disable-next-line react-hooks/exhaustive-deps -- load once on mount
-  }, [])
+  }, [loadQueue])
+
+  // ── SSE subscription ──
+  // Refetch the queue on each `handoff_created` event (the event payload is
+  // intentionally thin — it's a trigger, not the full card data). Diff
+  // against the previous list to identify newly-arrived sessions; prepend
+  // them at the top with the slide-in animation, then keep the rest of the
+  // queue in oldest-first order below.
+  const handleHandoffCreated = useCallback(async () => {
+    let fresh: AISessionSummary[]
+    try {
+      fresh = await aiSessionsApi.getEscalationQueue()
+    } catch {
+      return
+    }
+
+    const prevIds = new Set(sessionsRef.current.map((s) => s.id))
+    const arrived = fresh.filter((s) => !prevIds.has(s.id)).sort(sortNewestFirst)
+    const established = fresh.filter((s) => prevIds.has(s.id)).sort(sortOldestFirst)
+    const next = [...arrived, ...established]
+    setSessions(next)
+    onCountChange?.(next.length)
+
+    if (arrived.length === 0) return
+
+    const arrivedIds = arrived.map((s) => s.id)
+    setNewIds((prev) => {
+      const merged = new Set(prev)
+      arrivedIds.forEach((id) => merged.add(id))
+      return merged
+    })
+    if (document.hidden) {
+      setUnseenCount((c) => c + arrived.length)
+    }
+    window.setTimeout(() => {
+      setNewIds((prev) => {
+        const remaining = new Set(prev)
+        arrivedIds.forEach((id) => remaining.delete(id))
+        return remaining
+      })
+    }, NEW_CARD_HIGHLIGHT_MS)
+  }, [onCountChange])
+
+  useEffect(() => {
+    const abort = new AbortController()
+    let reconnectTimer: number | null = null
+    let attempt = 0
+    let cancelled = false
+
+    const connect = async () => {
+      if (cancelled) return
+      try {
+        await aiSessionsApi.streamEscalations(
+          {
+            onReady: () => {
+              attempt = 0
+            },
+            onHandoffCreated: () => {
+              void handleHandoffCreated()
+            },
+          },
+          abort.signal,
+        )
+        // Stream ended cleanly (server hung up). Reconnect quickly.
+        if (!cancelled) {
+          reconnectTimer = window.setTimeout(connect, 1000)
+        }
+      } catch (err) {
+        if (cancelled || abort.signal.aborted) return
+        if (err instanceof DOMException && err.name === 'AbortError') return
+        // Exponential backoff: 1s, 2s, 4s, 8s, 16s, capped at 30s.
+        const delay = Math.min(30_000, 1000 * 2 ** attempt)
+        attempt += 1
+        reconnectTimer = window.setTimeout(connect, delay)
+      }
+    }
+
+    void connect()
+
+    return () => {
+      cancelled = true
+      abort.abort()
+      if (reconnectTimer !== null) window.clearTimeout(reconnectTimer)
+    }
+  }, [handleHandoffCreated])
 
   const handlePickup = (sessionId: string) => {
     if (onPickup) {
@@ -95,7 +238,10 @@ export function EscalationQueue({ onPickup, onCountChange }: EscalationQueueProp
   return (
     <div className="space-y-3">
       <div className="flex items-center justify-between px-1">
-        <h3 className="font-sans text-[0.625rem] uppercase tracking-wider text-muted-foreground">
+        <h3
+          className="font-sans text-[0.625rem] uppercase tracking-wider text-muted-foreground"
+          aria-label={`${sessions.length} escalations awaiting pickup`}
+        >
           Awaiting pickup ({sessions.length})
         </h3>
         <button
@@ -107,54 +253,66 @@ export function EscalationQueue({ onPickup, onCountChange }: EscalationQueueProp
         </button>
       </div>
 
-      {sessions.map((session) => (
-        <div key={session.id} className="card-flat p-3 sm:p-4 space-y-3">
-          <div>
-            <p className="text-sm font-semibold text-foreground">
-              {session.problem_summary || 'Untitled session'}
-            </p>
-            {session.escalation_reason && (
-              <p className="mt-1 text-xs text-warning line-clamp-2">
-                Reason: {session.escalation_reason}
-              </p>
-            )}
-          </div>
-
-          <div className="flex flex-wrap items-center gap-x-3 gap-y-1 text-xs text-muted-foreground">
-            {session.problem_domain && (
-              <span className="font-sans rounded-md bg-accent-dim px-1.5 py-0.5 text-[0.5625rem] uppercase tracking-wider text-accent-text">
-                {session.problem_domain}
-              </span>
-            )}
-            <span className="flex items-center gap-1">
-              <Hash size={10} />
-              {session.step_count} steps
-            </span>
-            <span
-              className="flex items-center gap-1 font-medium"
-              style={{ color: waitTimeColor(session.created_at) }}
+      <div role="region" aria-live="polite" className="space-y-3">
+        {sessions.map((session) => {
+          const isNew = newIds.has(session.id)
+          return (
+            <div
+              key={session.id}
+              className={cn(
+                'card-flat p-3 sm:p-4 space-y-3',
+                isNew && !prefersReducedMotion && 'animate-slide-in-bottom',
+                isNew && prefersReducedMotion && 'animate-fade-in',
+              )}
             >
-              <Clock size={10} />
-              {timeAgo(session.created_at)}
-            </span>
-            {session.psa_ticket_id && (
-              <span className="flex items-center gap-1 text-accent-text">
-                <Ticket size={10} />
-                #{session.psa_ticket_id}
-              </span>
-            )}
-          </div>
+              <div>
+                <p className="text-sm font-semibold text-foreground">
+                  {session.problem_summary || 'Untitled session'}
+                </p>
+                {session.escalation_reason && (
+                  <p className="mt-1 text-xs text-warning line-clamp-2">
+                    Reason: {session.escalation_reason}
+                  </p>
+                )}
+              </div>
 
-          <div className="flex justify-end">
-            <button
-              onClick={() => handlePickup(session.id)}
-              className="rounded-lg bg-primary text-white px-4 py-2 text-sm font-semibold hover:brightness-110 active:scale-[0.98] transition-all"
-            >
-              Pick Up
-            </button>
-          </div>
-        </div>
-      ))}
+              <div className="flex flex-wrap items-center gap-x-3 gap-y-1 text-xs text-muted-foreground">
+                {session.problem_domain && (
+                  <span className="font-sans rounded-md bg-accent-dim px-1.5 py-0.5 text-[0.5625rem] uppercase tracking-wider text-accent-text">
+                    {session.problem_domain}
+                  </span>
+                )}
+                <span className="flex items-center gap-1">
+                  <Hash size={10} />
+                  {session.step_count} steps
+                </span>
+                <span
+                  className="flex items-center gap-1 font-medium"
+                  style={{ color: waitTimeColor(session.created_at) }}
+                >
+                  <Clock size={10} />
+                  {timeAgo(session.created_at)}
+                </span>
+                {session.psa_ticket_id && (
+                  <span className="flex items-center gap-1 text-accent-text">
+                    <Ticket size={10} />
+                    #{session.psa_ticket_id}
+                  </span>
+                )}
+              </div>
+
+              <div className="flex justify-end">
+                <button
+                  onClick={() => handlePickup(session.id)}
+                  className="rounded-lg bg-primary text-white px-4 py-2.5 text-sm font-semibold hover:brightness-110 active:scale-[0.98] transition-all"
+                >
+                  Pick Up
+                </button>
+              </div>
+            </div>
+          )
+        })}
+      </div>
     </div>
   )
 }

frontend/src/types/ai-session.ts

@@ -258,3 +258,23 @@ export interface SimilarSession {
   created_at: string | null
   similarity: number
 }
+
+// ── Escalation SSE bus ──
+//
+// Mirrors the `event_generator` payload in
+// backend/app/api/endpoints/session_handoffs.py — keep this in sync with the
+// dict published by `HandoffManager.dispatch_escalation_notifications`.
+
+export interface HandoffCreatedEvent {
+  type: 'handoff_created'
+  handoff_id: string
+  session_id: string
+  priority: string
+  engineer_notes: string
+  created_at: string | null
+}
+
+export interface EscalationStreamHandlers {
+  onReady?: () => void
+  onHandoffCreated?: (event: HandoffCreatedEvent) => void
+}