Changelog

[Unreleased]

UnixServer(path, handler, *, mode=0o600, backlog=16) — threaded Unix-domain-socket server speaking JSON lines. Auto-cleans stale socket files; refuses to overwrite a live socket. Handler exceptions are returned to the client as {"error", "type"} envelopes; the server keeps serving. Context-manager protocol.
UnixClient(path, *, timeout=5.0, retries=3, retry_backoff=0.5) — synchronous client with request() (round-trip) and notify() (fire-and-forget). Exponential backoff retry on ConnectionRefusedError / FileNotFoundError.
JsonLineProtocol — framing helper. encode(payload) → bytes and decode_stream(reader) generator over a binary stream.
FifoChannel(path, *, mode=0o600) — JSON-line over a named pipe. Auto-creates the FIFO; non-blocking send() (raises BrokenPipeError when no reader is attached); blocking recv().
pidfile(path) — context manager that writes the current PID, takes an exclusive flock advisory lock, and removes the file on exit. Raises BlockingIOError if another process already holds the lock — drop-in "don't start twice" guard for sidecar daemons.