fix(web): add exponential backoff + max retries to SSE reconnect

SSE reconnect was looping infinitely when the stream kept dropping
(e.g. during long Claude thinking pauses). Now uses exponential
backoff (2s, 4s, 8s, 16s, 32s) with a max of 5 retries. Counter
resets on successful connection.

Author: mariuspruvot

apps/web/src/features/session/ContainerSession.tsx

@@ -51,10 +51,14 @@ export default function ContainerSession({
 
   const lineIdRef = useRef(0)
   const sseOffsetRef = useRef(0)
+  const reconnectCountRef = useRef(0)
   const eventSourceRef = useRef<EventSource | null>(null)
   const mountedRef = useRef(true)
   const inputRef = useRef<HTMLInputElement>(null)
 
+  const MAX_RECONNECTS = 5
+  const RECONNECT_BASE_DELAY_MS = 2000
+
   const appendLine = useCallback((text: string, kind?: TerminalLine['kind']) => {
     if (!mountedRef.current) return
     lineIdRef.current += 1
@@ -73,6 +77,7 @@ export default function ContainerSession({
     const abortController = new AbortController()
     lineIdRef.current = 0
     sseOffsetRef.current = 0
+    reconnectCountRef.current = 0
     setLines([])
 
     async function init() {
@@ -111,6 +116,19 @@ export default function ContainerSession({
     }
 
     async function pollSessionStatus(sessionId: string) {
+      reconnectCountRef.current += 1
+      if (reconnectCountRef.current > MAX_RECONNECTS) {
+        setStatus('failed')
+        setError('Lost connection to session')
+        appendLine('[error] Lost connection after multiple retries.')
+        return
+      }
+
+      // Exponential backoff: 2s, 4s, 8s, 16s, 32s
+      const delay = RECONNECT_BASE_DELAY_MS * Math.pow(2, reconnectCountRef.current - 1)
+      await new Promise((r) => setTimeout(r, delay))
+      if (!mountedRef.current) return
+
       try {
         const fresh = await getContainerSession(sessionId)
         if (!mountedRef.current) return
@@ -121,7 +139,6 @@ export default function ContainerSession({
           setError('Container failed')
           appendLine('[error] Container failed.')
         } else if (fresh.status === 'running') {
-          appendLine('[reconnecting] Stream dropped, container still running...')
           connectStream(sessionId)
         }
       } catch {
@@ -146,6 +163,8 @@ export default function ContainerSession({
       source.addEventListener('open', () => {
         if (!mountedRef.current) return
         setStatus('running')
+        // Connection succeeded — reset reconnect counter
+        reconnectCountRef.current = 0
       })
 
       // Default message event — parse Claude Code stream-json