Issue 24549 runtime reproduction
Before commit: 3afb9b366f271b56a3e49fd86f2594981ec11b66
Environment: Linux x86_64 fs-06; real web dev server, T3 collaborative Chromium browser 1280x800, light theme; OpenCode 2.1.2; anthropic/claude-haiku-5-5 through configured hub.
Isolated state: /home/ubuntu/wt/issue-24549/.t3; no writes to live T3 database.
Attempt 1, normal event delivery, 21:36 UTC:
- Complete prompt: Reply with just hello. Do not use tools.
- Start: Run sleep 60 in the shell, then reply done. Do not change files.
- Click Stop generation, Fork from this response on earlier hello response, send Reply with fork works. Do not use tools.
- Result: fork replied 'fork works'. No protocol error.
Attempt 2, controlled lost-event delivery, 21:38-21:39 UTC:
- Run real OpenCode serve behind proxy.cjs at localhost:18166; configure T3 provider Server URL to this proxy; restart isolated dev server to use new connection.
- Proxy forwards real API calls and events, dropping only SSE frames containing session.execution.interrupted. No provider replies or data are stubbed.
- Complete hello response. Start Run sleep 60 in shell then reply done. Do not edit files.
- Wait for Running sleep. Click Stop generation. Fork earlier assistant response. Send Reply fork works.
- Proxy log: DROPPED interrupted terminal event 2026-10-24T21:38:56.362Z (three subscribers).
- Result: Provider turn failed to start; opencode provider protocol error: Cannot fork OpenCode session ses_e902693daffeOzPRgk7L9HAwYs while it is still working.
- Source lineage displays Stopped. Fork thread exists with inherited history.