Cell F4 (ENG-2592). Attribution source: F1's first-party request without a Referer, and a cross-origin same-site fetch carrying only Origin. Brave keys on the initiator and is unaffected. Ours: Referer and Origin are confident sources; a request with neither falls back to TopLevelUrlSource.Self, which is not confident, so the first-party gate fails safe to blocked (ENG-2391 confidence rule, AdblockFilteringEngine.cs:711-714). The MV3 extension's top frame (Extension) is not counted as confident either, so the extension context feed does not close this row today.
Rows, rules and Brave's verdicts are in pages/network-fixtures.json. The runner grades from CDP, never from this page.