Force fresh document loads in same-port visual comparisons

Reusable visual-regression method observed 2026-09-08 during COR-4091 localhost verification: swapping two builds behind the same host, port, and asset URLs can leave a browser tab displaying the previous build's stylesheet even when the fixture sends no-store. A reliable matched comparison should load each route with a unique document query (or otherwise force a full reload), then assert one or more computed design tokens before capturing. In this case the token check caught a contaminated baseline immediately: the expected staging canvas was #101513 while the stale tab still rendered the replacement #070707. Source provenance: loopback synthetic fixture plus browser-computed CSS values; no live service data.