CVE-2026-70606: Electron: ProtocolResponse.url reuses the default session cache instead of the registering session

When a custom protocol handler returned a ProtocolResponse with a url and no session, Electron made the upstream request through defaultSession instead of the session that handled the protocol. A cached response could then be reused across otherwise isolated session partitions.

Apps that use ProtocolResponse.url, omit ProtocolResponse.session, and rely on separate sessions to isolate content are affected. Apps that set an explicit session, or that do not isolate content across sessions, are not affected.