Testing with Playwright

A running mock server accepts overrides over plain HTTP, so a Playwright test can shape one
operation's response for the duration of a single test, then reset it back to the document's
generated baseline before the next test runs:

Wire the mock server into playwright.config.ts's webServer option alongside the app itself,
then reset runtime overrides in afterEach so a failed assertion cannot leak state into the next
test:

test.afterEach(async ({ request }) => {
  await request.post("http://localhost:4010/@fusion-mock/reset");
});

test("shows fallback UI when context resolution fails", async ({ page, request }) => {
  await request.post("http://localhost:4010/@fusion-mock/context/getContext", {
    data: { status: 404, mock: { error: "not found" } },
  });

  await page.goto("/some-context-dependent-page");
  await expect(page.getByText("Context not found")).toBeVisible();
});

The control request targets an OpenAPI operationId, not a URL path. Omitting status preserves
that operation's baseline status while replacing its response body.

See cookbooks/app-react-mock-playwright
for a full app wired up this way, including its playwright.config.ts's webServer entry for
ffc mock-server.

Routes

Every override goes through the /@fusion-mock/ control plane; everything else is proxied to the
matching service's own mock:

Route	Method	Purpose
/@fusion-mock/discovery	GET	Service-discovery response for each discovery-visible service: its key and http://<key>.localhost:<port> origin. Direct-only definitions using serviceDiscovery: false remain routable but are omitted.
/@fusion-mock/health	GET	200 OK once the server is ready.
/@fusion-mock/reset	POST	Discards runtime operation overrides and rebuilds each source-defined baseline, including declarative defineService routes.
/@fusion-mock/:service/:operationId	POST	Registers a one-off override for that operation; body is { status?: number, mock: unknown }.
http://<service>.localhost:<port>/*	any	Resolved against that service's middleware first, then its OpenAPI mock, using its discovered origin.
/:service/*	any	Same service-relative behavior, for embedding without relying on *.localhost DNS resolution.

Override bodies missing the required mock field return 400; unknown service keys and
unmatched data-plane operations return 404. Invalid JSON, source-resolution failures, and
unexpected handler failures return 500 with an error body.

Avoid naming a service @fusion-mock — that segment is always routed to the control plane
first, so a service with that exact key would be unreachable. health, discovery, and reset
are only reserved as paths under /@fusion-mock/; a service named e.g. health is still
reachable at /health/* or health.localhost.