Web UI freezes after SSE reconnect — missed events not recovered #13947

Description

When the SSE event stream (/global/event) drops and reconnects, the web UI never re-fetches state from the server. Events missed during the disconnect are permanently lost — the session timer keeps running but no new content appears. Only a manual page refresh recovers the UI.

Root cause: applyGlobalEvent in event-reducer.ts ignores server.connected events. After SSE reconnection the client gets a fresh stream but has no idea it missed anything.

Secondary issues:

• The 30s heartbeat interval is too slow to detect dead connections through buffering reverse proxies (Tailscale serve, nginx, etc.)
• The frontend proxy catch-all hardcodes app.opencode.ai with no way to override it for self-hosted patched frontends

Steps to reproduce

1. Open the web UI through any reverse proxy (Tailscale serve, nginx, Cloudflare Tunnel) or on a mobile browser
2. Start an agent session
3. Wait for the SSE connection to drop (switch WiFi, put phone to background, or proxy idle timeout)
4. Observe: timer keeps counting but content stops updating
5. Refresh Chrome → UI shows the completed state that was missed

Also reproducible without a proxy by switching networks mid-session on mobile.

Fix

Working patch on my fork (2 commits): https://github.com/rich-jojo/opencode/pull/1

Commit 1 — SSE reconnect recovery:

• event-reducer.ts: treat server.connected like global.disposed → call refresh() to re-bootstrap state
• SSE endpoints: add X-Accel-Buffering: no header, reduce heartbeat 30s→10s
• global-sdk.tsx: add client-side heartbeat timeout (15s) + visibilitychange reconnect

Commit 2 — configurable frontend proxy:

• server.ts: read OPENCODE_APP_URL env var in the catch-all route (falls back to app.opencode.ai)

Running both patches in production (opencode web via Tailscale serve, accessed from Android Chrome). UI now recovers within seconds after any connection drop.

OpenCode version

v1.2.6

Operating System

Ubuntu 24.04 (server), Android Chrome (client)