Phase 1 of PRD 0014. Adds the in-sidecar SIGHUP signal handler that
re-reads routes.json + re-resolves tokens from env without dropping
in-flight connections:
- reload_routes(server, path, environ=...) does the atomic swap.
Returns (ok, message) so the caller can log/surface failures.
On failure (bad JSON, missing file) the server keeps serving the
old routes rather than dying — typos shouldn't crash the sidecar.
- install_sighup_handler wires SIGHUP → reload_routes. No-op on
platforms without SIGHUP (Windows).
- serve() now installs the handler at startup.
Atomicity: Python attribute reassignment is atomic, and the request
handler reads server.routes/tokens once at the top of _proxy() so
an in-flight request keeps the version it captured.
Tests cover successful reload, JSON-parse failure, and missing-file
failure (both verify the old routes survive).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
didericis
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