UI hangs indefinitely when LLM stream fails mid-flight (fetch failed / network drop) #46583

Description

The TUI freezes and becomes unresponsive when the LLM provider stream errors out mid-flight with a "fetch failed" error. The UI enters a waiting state with no recovery path — no timeout fires, and the interface stays frozen indefinitely while the process continues to consume ~31% CPU in a render loop.

Steps to Reproduce

1. Start opencode with an LLM provider that requires a network connection
2. Send a message to the agent
3. Have the network connection drop or the provider return an error mid-stream
4. Observe: the UI freezes and never recovers

Expected Behavior

The UI should detect the stream failure and display an error, allowing the user to retry or exit cleanly.

Actual Behavior

• TUI hangs indefinitely — no error displayed, no way to recover without killing the process
• Process stays alive consuming ~31% CPU (stat: Rl+)
• Main thread blocked on ep_poll (epoll waiting for I/O that never arrives)
• Log shows the stream error was recorded, but the UI never unblocks

Log Evidence

level=ERROR message="stream error" providerID=zcode modelID=claude-sonnet-4-6
  agent=title error.error.type=api_error error.error.message="fetch failed"

level=ERROR message="stream error" providerID=zcode modelID=claude-sonnet-4-6
  agent=build error.error.type=api_error error.error.message="fetch failed"

The title agent failed at T+0:05, the build agent at T+2:21. After that, the UI was frozen for 5+ hours until manually killed.

Sequence of Events

10:13:10  models.dev fetch → TimeoutError
10:16:40  New session created, user message sent
10:16:45  Title agent stream → "fetch failed"
10:19:06  Build agent stream → "fetch failed"
          ← UI freezes here, no recovery

Process Snapshot (at hang)

PID   STAT  %CPU  THREADS  ELAPSED  WCHAN
58867  Rl+   31.1    33     4:08:31  ep_poll

• 33 threads, most in futex_wait (normal)
• Main thread: ep_poll — blocked waiting for I/O event that never fires
• No subprocess leak, no DB lock, SQLite WAL clean

Environment

• opencode version: 1.18.25
• OS: Ubuntu 24.04.4 LTS (Noble Numbat)
• Kernel: 6.8.0-138-generic
• Platform: Linux x86_64
• Node: v24 (Bun runtime)
• Provider: zcode (Claude Sonnet 4.6 proxy)

Suggested Fix

Add a stream-level timeout or watchdog: if a stream has errored and the promise has not resolved within N seconds, surface the error in the UI and unblock the render loop. A Promise.race(stream, timeout) pattern around the provider stream would prevent the indefinite wait.