Introduces an OpenCode chat harness alongside Claude, driven over HTTP + SSE against
a persistent `opencode serve`, emitting the same ChatEvent contract so the entire
chat UI and createEventHandler pipeline are unchanged.
New servers/api/chat/opencode/:
- server-manager.ts — one warm `opencode serve` per cwd (free port, health-gated,
respawn on exit; HOME set so it reads the user's ~/.local/share/opencode auth).
Binary pinned via OPENCODE_BIN (installed is 1.17.9; the 1.18.4 upgrade never landed).
- client.ts — per-server HTTP calls (/session create, /message, /abort) + a single
reconnecting `/event` SSE stream demuxed to per-session listeners.
- event-mapper.ts — SSE → ChatEvent. Verified live against 1.17.9: message.part.delta
→ delta, tool parts → tool:start/tool:result, message.updated → cost, session.idle
→ result. Crucially, deltas are gated on partID being a `text` part (declared before
its deltas) so the model's reasoning — which also streams as field:'text' — is
dropped, matching the Claude harness hiding thinking.
- state.ts — sessionKey ↔ opencode ses_ id map for resume.
channels/send-opencode.ts — the OpenCode analog of send-claude-code: ensure serve,
create/reuse session, subscribe, post the message, forward mapped events; kill = abort.
websocket.ts — replaces the Claude-only coercion with harness routing:
provider 'claude-code' → Claude sidecar, everything else → handleOpenCodeChat.
handleStop aborts the right harness.
Verified end-to-end (streaming text, tool call/result, cost, abort) against a
throwaway serve using the free deepseek model — no prod restart involved. UI-level
model selection + session history follow in Phases 2–3.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
