Headless Linux, Chromium through T3 Code collaborative preview.
Production publishable key from repository .env.example; no sign-in performed.

Main baseline at http://localhost:6696:
window.Clerk exists; frontendApi=clerk.t3.codes; instanceType=production; loaded=false.
Console: Clerk: Production Keys are only allowed for domain "t3.codes".
API Error: The Request HTTP Origin header must be equal to or a subdomain of the requesting URL.
Clerk SDK requests returned HTTP 400. The local app still rendered, but cloud authentication could not initialize.

Guarded local app at the same origin:
window.Clerk absent; no Clerk runtime mounted. Connections settings renders ordinary local network access, authorized clients, and Add environment.

Supported hosted origin https://app.t3.codes, fresh incognito profile:
window.Clerk exists; frontendApi=clerk.t3.codes; loaded=true.
Welcome displays T3 Connect / Sign in and Add a computer. No authentication was attempted.

Raw /v1/environment probes were inconsistent due cached responses and were not used as origin acceptance proof. No claim is made about nonstandard HTTPS ports beyond Clerk's published requirements.