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conformance · v140

v140 · serviceworkerautopreload-browser-mode / race-in-practice — conformance probe

3 assertions drawn from the spec. Each is a single contract the spec text makes. Pass/fail reflects what this browser executed; blocked means the contract was not run because it needs user mediation, hardware, or another unavailable precondition. Open the page in Chrome stable / canary / Firefox / Safari to compare.

browser: spec: https://w3c.github.io/ServiceWorker/#dom-installevent-addroutes chromestatus: #5194817700364288 generated 2026-08-28T00:00:00Z by claude-opus-5-v140-additive
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id contract kind verdict detail
a-streamed-response-resolves-before-its-body The finding this page rests on: fetch resolves when the response's headers arrive, not when its body finishes. That is why a race against a slow stream is decided on time-to-first-byte, and why the crossover measured here is so low. spec ↗ script
the-slow-stream-fixture-is-actually-slow The network side of the race is a server route that paces its chunks. If it returned instantly the race would have nothing to race, and every reading on this page would be noise. spec ↗ script
custom-headers-survive-a-synthesised-response The winner of each race is read from x-served-by rather than guessed from the duration — which would be circular, since the duration is the thing being explained. spec ↗ script