Cookie transport

[vitalets]

Along with custom header transport, it would be useful to support cookie transport of mocks. It will make easier integration with test runners and other tools (e.g. browser extensions).

Proof of concept

We can serialize mocks into a cookie named x-mock-request and check this cookie on server.

Caveats

Header is stateless, but cookie is stateful. Maybe we need to provide methods to clear the mocking cookie.

[vitalets]

Investigation summary:

The core server-side change is minimal — extractMockSchemas already receives the full incoming headers, so adding a cookie fallback is straightforward: check x-mock-request header first, fall back to parsing Cookie: x-mock-request=<value>. No interceptor or MockClient API changes needed.

The tricky part is the client side (e.g. browser extensions). Cookies are stateful unlike headers, so we'd need helpers for both setting and clearing the mock cookie. More importantly, setting cookies from a browser extension requires the cookies permission in the manifest — an extra permission that users may not want to grant.

Decision: Deferring cookie transport for now. For the browser extension use case, the existing header approach works via the debugger permission (already required for network interception), so there's no practical gap. Cookie transport can be revisited if a compelling use case emerges that can't be served by headers.