Read an empty supervisor PORT as unset, so NaN never reaches Bun.serve

[Bartok9]

What this changes

The supervisor read Number.parseInt(process.env.PORT ?? "4300", 10). ?? only fires on undefined. An empty PORT= from compose or a leftover .env line is "", so parse became NaN and Bun.serve({ port: NaN }) bound an ephemeral port while compose still published 4300 — the same empty-string trap the API server fixed in #312/#340 and the computer saw in #96/#114. Prefix typos like 30o0 also started on port 30 via parseInt.

Empty/whitespace now means the default 4300. Non-numeric or out-of-range values refuse boot with a clear message. Parser lives in supervisor/src/listen-port.ts with unit tests (no Docker).

Where it runs

• New state that outlives a request? None. Boot-time number.
• What happens on the second replica? Each supervisor reads its own env; empty still means 4300 on that process.
• Anything serialised? No.
• Anything fanned out to a browser? No.
• New listener, port, or schedule? No — same listener, correct bind address.

Boundary and audit

• Every acting call still goes through the gateway: untouched.
• New refusals and new failures each write a row: boot refusal exits before DB; same shape as missing SUPERVISOR_TOKEN.
• Nothing new is trusted from the client.

Changelog

• Unreleased section: empty supervisor PORT is unset, not an ephemeral bind.

Proof

Node smoke of listenPort (empty → 4300; 4500 → 4500; 30o0/0/65536 refused). Added supervisor/tests/listen-port.test.ts for bun test.