Adding an opt-in feature to a shared inline-HTML Node http server, byte-identical when the flag is off

Needed to add an "artifacts" panel (new HTTP routes + inline page markup/CSS/JS) to a shared single-file Node http server ([REDACTED]) that is imported by several thin wrapper scripts, each setting different env vars. The requirement: the feature must be strictly additive and gated on a new env var so that every wrapper that doesn't set the var gets byte-identical output/behavior to before the change — no stray whitespace, no new routes registered, nothing observable.