move opencode's turn output into its own sidecar

The second copy of the same problem. The opencode sidecar reported raw
ChatEvents and officer translated them, buffered the assistant text and wrote
every durable message to chat_session_events — so an officer restart mid-turn
lost whatever the model had produced since the last write, and `connect.ts`
dropped the events that arrived while it was down without a word.

Both harnesses speak ChatEvents, so the sidecar reuses the agent's session log
verbatim: translate, commit, then deliver the finished message with its cursor
id as `opencode:message`. Officer folds it into the in-memory transcript and
relays it, exactly as it now does for claude — `createEventHandler` (166 lines,
a duplicate of turn-stream.ts) and `emitToSession` are gone, and nothing in
officer writes to chat_session_events any more.

`opencode:event` stops being a wire event; it is the runner's internal report to
the sidecar it runs in, typed as such so it cannot leak back onto the socket.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/servers/sidecar/opencode/runner.ts

@@ -1,7 +1,7 @@
 import { existsSync } from 'node:fs';
 import type { Subprocess } from 'bun';
 import type { ChatEvent, MessageCost } from '../../api/chat/types';
-import type { OpenCodeRunParams, SidecarEvent } from '../protocol';
+import type { OpenCodeRunParams } from '../protocol';
 
 // Drives one chat turn by spawning `opencode run … --format json` and mapping its newline-delimited
 // JSON events to the shared ChatEvent contract. This is the reliable path: `--dir <cwd>` hard-anchors
@@ -21,7 +21,14 @@ export type RunnerConfig = {
   fallbackCwd: string; // used when params.cwd is missing/nonexistent
 };
 
-type Emit = (event: SidecarEvent) => void;
+// What a turn reports to the sidecar it runs in. `opencode:event` is deliberately not a wire event any
+// more: the sidecar translates each one into a TurnMessage and commits it before officer sees anything,
+// so the durable record does not depend on officer being up (see index.ts).
+export type RunnerMessage =
+  | { type: 'opencode:event'; sessionKey: string; event: ChatEvent }
+  | { type: 'opencode:session'; sessionKey: string; sessionId: string };
+
+type Emit = (msg: RunnerMessage) => void;
 
 type RunHandle = { proc: Subprocess; killedByUser: boolean };
 
@@ -108,7 +115,10 @@ export function runOpenCodeTurn(params: OpenCodeRunParams, config: RunnerConfig,
       } catch {
         /* already gone */
       }
-      finish({ type: 'error', message: `OpenCode turn stalled (no output for ${INACTIVITY_MS / 1000}s) and was stopped` });
+      finish({
+        type: 'error',
+        message: `OpenCode turn stalled (no output for ${INACTIVITY_MS / 1000}s) and was stopped`,
+      });
     }, INACTIVITY_MS);
   };
   bumpInactivity();