Sink-based structured logger producing JSON line output with deterministic field ordering. The sink abstraction allows output destinations (stdout, file, etc.) to be swapped without changing call sites. Demonstrates a clean separation between log emission and transport, reusable in any TypeScript service.

Typed error constant system used across all modules. Centralizes error codes into a single typed namespace, enabling consistent error handling and cross-module error propagation. The pattern of a typed error code registry is directly transferable to other TypeScript applications that need structured, greppable error semantics.

JSON-RPC client over stdin/stdout for driving the Codex app-server, with dynamic tool injection. Demonstrates a robust subprocess IPC pattern: request/response correlation, event streaming, and tool registration. The client abstraction isolates the wire protocol from the rest of the orchestrator, making it adaptable to other agent runtimes.

A fake Codex app-server implementing the JSON-RPC protocol for tests, with configurable scenarios (happy path, timeouts, user-input, linear tool). This is a novel test pattern: a protocol-level simulation harness that lets tests exercise the full client stack without a real Codex binary. The scenario-based approach is reusable for testing any subprocess-based agent client.