design-code-proxy startup log hardcodes backend ports — misreports custom ANTIGRAVITY_LS_PROXY_PORT/CODEX_PROXY_PORT #496

Problem

bin/design-code-proxy.mjs's startup "Backends" log line hardcodes the two backend ports, although both are now strictly validated environment variables in the same file. With custom ports configured, the log misreports where the proxy will actually route — the exact diagnostic an operator reads first when a backend is unreachable.

Evidence (verified on main d7a6d90)

• bin/design-code-proxy.mjs:8-9 parses the real values:

  • ANTIGRAVITY_LS_PORT = parseProxyPort('ANTIGRAVITY_LS_PROXY_PORT', 18745)
  • CODEX_PROXY_PORT = parseProxyPort('CODEX_PROXY_PORT', 18744)
    (strict validation added by PR fix(bin): validate *_PROXY_PORT strictly in all five proxies #493, closing bin proxies: *_PROXY_PORT parsed with bare parseInt — invalid values crash opaquely or bind the wrong port #483.)

• The route table (bin/design-code-proxy.mjs:17-27, the MODELS entries) uses those parsed variables.

• But bin/design-code-proxy.mjs:302 logs literals:

  console.log(`[design-code-proxy] Backends: Antigravity LS (18745), Codex (18744), AMR Upstream (${AMR_UPSTREAM_URL})`);

  The adjacent Listening line (:301) correctly interpolates ${PORT}.

• Live repro this run:

  $ DESIGN_CODE_PROXY_PORT=19003 ANTIGRAVITY_LS_PROXY_PORT=19001 CODEX_PROXY_PORT=19002 node bin/design-code-proxy.mjs
  [design-code-proxy] Listening on http://127.0.0.1:19003
  [design-code-proxy] Backends: Antigravity LS (18745), Codex (18744), AMR Upstream (https://amr-link.open-design.ai/v1)
  

  The proxy routes to 19001/19002 but the log claims 18745/18744.

• Dedup: no open or recently closed issue names the Backends log line (searched "design-code-proxy Backends log" and "hardcoded ports startup log"). The other four proxies' startup lines interpolate ${PORT} and name no backend ports — this is the only site. The bin proxies exist only in this repo.

Why it matters

Custom backend ports are a supported configuration (#483/#493 made them strictly validated env vars, and #434 adds {env:VAR:-fallback} substitution for these proxy base URLs). An operator debugging a failed backend with non-default ports will be told by the proxy's own log that it is talking to ports it is not using.

Acceptance criteria

• The Backends log line interpolates the parsed ANTIGRAVITY_LS_PORT / CODEX_PROXY_PORT values instead of the literals 18745/18744.
• With custom ANTIGRAVITY_LS_PROXY_PORT / CODEX_PROXY_PORT set, the startup log shows those ports; with defaults, output is unchanged.
• Existing bin/proxy-port.test.mjs suite still passes.