When an MCP host (opencode and others) SIGTERM's the shared daemon as a new
session starts, the existing session's proxy used to exit on the dropped socket
— silently losing CodeGraph for that session, and hanging any request in flight
at the drop. The SIGTERM originates in the host's process-tree teardown, not in
CodeGraph (nothing here signals another process), so the fix is proxy
resilience, not chasing the signal.
The local-handshake proxy now treats a daemon disconnect as recoverable rather
than terminal: it falls back to its in-process engine for the rest of the
session (the same path used when no daemon is reachable at startup, and what
CODEGRAPH_NO_DAEMON does) and re-serves any requests that were in flight to the
dead daemon, so the host never hangs. The proxy still exits when the HOST goes
away (stdin close / PPID watchdog) — only daemon loss is now non-fatal.
Also replaces the over-the-wire liveness-sweep test added in #712 — which was
flaky under heavy parallel load (a raced raw-socket connect) — with a
deterministic Daemon.reapDeadClients unit test. The client-hello round-trip is
still exercised by every daemon test (the real proxy now sends it).
Validated with a reproduction (proxy stays alive, in-flight request answered,
post-drop request recovers) and a regression test in mcp-daemon.test.ts.
Confirmed on macOS (full suite green) and a Windows 11 VM.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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