feat(flywheel-c2-c3): C2 hasType4接真實API + C3 WebSocket指數退避重連

C2: flywheel_stats_service 加 type4_count query → API 回傳
    flywheel-diagram.tsx hasType4 改由 type4Count prop 驅動（非 false）
    flywheel-kpi-card.tsx 傳入 type4Count={flowData?.type4_count}

C3: WebSocket onclose 加指數退避重連 (1s→2s→4s→最大30s)
    cancelled 旗標確保 unmount 後不重連
    wsRetryTimer 加入 cleanup

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/src/components/dashboard/flywheel-diagram.tsx

@@ -24,6 +24,8 @@ interface FlywheelDiagramProps {
   currentFlow?: FlowItem[]
   /** active node names from node_stats */
   activeNodes?: Record<string, { status: string }>
+  /** TYPE-4 active incident count from API (ADR-073-C C2) */
+  type4Count?: number
 }
 
 const NODES = [
@@ -44,7 +46,7 @@ function toSVG(pct: { x: number; y: number }) {
   return { cx: (pct.x / 100) * W, cy: (pct.y / 100) * H }
 }
 
-export function FlywheelDiagram({ currentFlow = [], activeNodes = {} }: FlywheelDiagramProps) {
+export function FlywheelDiagram({ currentFlow = [], activeNodes = {}, type4Count = 0 }: FlywheelDiagramProps) {
   // Count active incidents per node
   const nodeCounts: Record<string, number> = {}
   for (const f of currentFlow) {
@@ -52,7 +54,7 @@ export function FlywheelDiagram({ currentFlow = [], activeNodes = {} }: Flywheel
   }
 
   const hasType3 = currentFlow.some(f => f.current_node === 'reasoning' || f.current_node === 'execution')
-  const hasType4 = false // TYPE-4 shown when diagnosis node has stuck items
+  const hasType4 = type4Count > 0
 
   // Build arc path through nodes in order
   const pts = NODES.map(n => toSVG(n))

apps/web/src/components/dashboard/flywheel-kpi-card.tsx

@@ -31,7 +31,7 @@ interface FlywheelSummary {
 
 export function FlywheelKPICard() {
   const [data, setData] = useState<FlywheelSummary | null>(null)
-  const [flowData, setFlowData] = useState<{ current_flow: FlowItem[]; nodes: Record<string, { status: string }> } | null>(null)
+  const [flowData, setFlowData] = useState<{ current_flow: FlowItem[]; nodes: Record<string, { status: string }>; type4_count?: number } | null>(null)
   const [error, setError] = useState(false)
   const wsRef = useRef<WebSocket | null>(null)
 
@@ -55,14 +55,18 @@ export function FlywheelKPICard() {
 
     load()
 
-    // C3: WebSocket — upgrades from polling when available
+    // C3: WebSocket — upgrades from polling when available, with reconnect (ADR-073-C C3)
+    // 指數退避重連：1s → 2s → 4s → 8s → 最大 30s
+    let wsRetryDelay = 1000
+    let wsRetryTimer: ReturnType<typeof setTimeout> | null = null
+
     const connectWS = () => {
-      if (!WS_BASE) return
+      if (!WS_BASE || cancelled) return
       const ws = new WebSocket(`${WS_BASE}/api/v1/stats/flywheel/ws`)
       wsRef.current = ws
 
       ws.onopen = () => {
-        // WS connected — stop HTTP polling
+        wsRetryDelay = 1000  // 連線成功 — 重置退避
         if (pollId) { clearInterval(pollId); pollId = null }
       }
       ws.onmessage = (e) => {
@@ -75,10 +79,14 @@ export function FlywheelKPICard() {
         } catch { /* ignore malformed */ }
       }
       ws.onclose = () => {
-        // WS closed — fall back to polling
-        if (!cancelled && !pollId) {
-          pollId = setInterval(load, 30_000)
-        }
+        if (cancelled) return
+        // 退回 HTTP polling
+        if (!pollId) pollId = setInterval(load, 30_000)
+        // 指數退避重連
+        wsRetryTimer = setTimeout(() => {
+          wsRetryDelay = Math.min(wsRetryDelay * 2, 30_000)
+          connectWS()
+        }, wsRetryDelay)
       }
       ws.onerror = () => ws.close()
     }
@@ -90,6 +98,7 @@ export function FlywheelKPICard() {
     return () => {
       cancelled = true
       if (pollId) clearInterval(pollId)
+      if (wsRetryTimer) clearTimeout(wsRetryTimer)
       wsRef.current?.close()
     }
   }, [])
@@ -175,6 +184,7 @@ export function FlywheelKPICard() {
         <FlywheelDiagram
           currentFlow={flowData?.current_flow ?? []}
           activeNodes={flowData?.nodes ?? {}}
+          type4Count={flowData?.type4_count ?? 0}
         />
       </div>