Create packages/ext-agent-orchestrator/ — PubSub reactor extension pattern #70

What to build

Create packages/ext-agent-orchestrator/, a new package that establishes the documented extension pattern for all fork-specific orchestration work. Extensions subscribe to orchestrationEngine.streamDomainEvents, filter for relevant event types, and dispatch commands back through orchestrationEngine.dispatch() — never modifying decider.ts or ProviderCommandReactor.ts.

Package contents

1. README.md documenting the extension pattern with examples
2. Effect Service tag + Layer template for new reactors
3. A minimal example reactor (e.g., logging events to disk) that demonstrates subscribe → filter → dispatch
4. Proper package.json, tsconfig.json, and subpath exports

Pattern contract

// Extensions depend on the existing OrchestrationEngine service
// They NEVER import from decider.ts or modify core orchestration files
const makeMyReactor = Effect.gen(function* () {
  const engine = yield* OrchestrationEngineService;
  yield* engine.streamDomainEvents.pipe(
    Stream.filter(isMyEventType),
    Stream.runForEach((event) => /* react + dispatch */)
  );
});

This is HITL because the pattern becomes the architectural contract all future fork work must follow.

Acceptance criteria

• packages/ext-agent-orchestrator/ exists with correct package structure
• README.md documents the reactor extension pattern with code examples
• Minimal example reactor compiles and demonstrates subscribe → filter → dispatch
• vp check passes
• No changes to decider.ts, OrchestrationEngine.ts, or ProviderCommandReactor.ts

Blocked by

• Resolve upstream merge conflicts from t3-code/main fork #67 (Resolve upstream merge conflicts)