The interface being an MCP client is this architecture's central claim: it is why the tools are said to be provably sufficient, because the flagship interface is a client of them. No test joined the two halves. One test drove a real server and never touched a route; the others drove every route against a fake link, and the two assertions on /live/frame accepted every status the route can produce.
One request now goes through the whole chain with only the browser left out, and making the route reach the registry in-process instead turns it red. No engine is downloaded, so it runs by default.
Writing it found two things. The first version used TestClient, like every other route test here, and hung with no output: TestClient runs the app in its own event loop while a real Link holds its stdio streams in the test's. Every request is now bounded, so the next regression of that shape fails with a name instead of hanging a suite. And the first assertion was wrong about the product rather than the plumbing: browser_list reports the browsers that exist, not the two roles that could.
Also: server.json's description was the one duplicated fact nothing compared, and the file's own docstring still named a manifest removed in #1316.