fix(web): reconnect SSE stream when mobile tab becomes visible again - #39028

Problem

When using opencode serve or opencode web from a mobile browser (Chrome), switching to another app and coming back leaves the chat frozen. No new messages appear until the user manually refreshes the page.

Root cause

The SSE event stream in server-sdk.tsx only handles tab lifecycle via pagehide/pageshow, which are designed for bfcache (back-forward cache) navigation between pages. On mobile:

1. pagehide often does not fire when the tab is backgrounded by switching apps
2. When it does fire, it calls stop() which aborts the SSE connection and cancels server-side generation
3. pageshow fires with persisted=false on resume (not a bfcache restore), so resumeStreamAfterPageShow returns without restarting the stream
4. The stream stays dead until manual refresh

Fix

• Add a restart() helper that safely tears down and recreates the SSE connection
• Listen to document.visibilitychange and call restart() when the page becomes visible
• Do NOT stop the stream on hidden, preserving server-side generation

+  const restart = () => {
+    started = false
+    generation++
+    attempt?.abort()
+    return start()
+  }
+
   onMount(() => {
     makeEventListener(window, "pagehide", stop)
     makeEventListener(window, "pageshow", (event) => resumeStreamAfterPageShow(event, start))
+    makeEventListener(document, "visibilitychange", () => {
+      if (document.visibilityState === "visible") restart()
+    })
   })

Testing

Tested on Android Chrome by initiating a long response, switching to another app, waiting several seconds, and returning. The response appeared without manual refresh.

Files changed

• packages/app/src/context/server-sdk.tsx — add restart() and visibilitychange listener