* test(proxy): keep answering requests while a cold /openapi.json builds
* fix(proxy): build the OpenAPI schema off the event loop so a cold /openapi.json no longer stalls the worker
* perf(proxy): reuse the rendered /openapi.json body until the schema changes
* fix(proxy): scope the openapi build's pydantic patch to the build
The schema build swapped a process-wide pydantic hook, which live requests saw once the build moved to a thread, and overlapping builds could leave it installed. The hook now checks a context variable set only inside the build. The proxy test counts liveliness answers instead of timing them.
* test(proxy): hold the cold openapi build on an event instead of pacing on a clock
* fix(proxy): serve a replaced app.openapi like FastAPI's own docs route
* test(proxy): build the cold-docs test on the proxy module's current app
* test(proxy): freeze the model that holds the cold docs build
