Keep request origin independent of URL resolution and referrer context,
including local blob fetches and inherited or sandboxed srcdoc documents.
Reject missing browser origins at the resource client boundary and retain
one Request across Service Worker redirects and network fallback.
Cover dispatch rejection, wire Origin/Cookie headers, memory-cache
partitioning and preserved Service Worker request metadata.
Validation: workspace fmt and Clippy passed; Nextest passed 17,517 tests
with 13 existing skips. Renderer test debug symbols were disabled to fit
available build memory; tests and debug assertions were unchanged.
ldm0