"""Mount a probe router on the shared app — and actually take it back off.

Several gate tests prove a negative ("an ungated route WOULD answer this
caller, so the sweep above isn't vacuous") by mounting a throwaway
``APIRouter`` on the real ``app.main:app``. That app is a process-global
shared by all ~15k tests, so anything mounted has to come back off.

The obvious teardown — filtering ``app.router.routes`` by ``.path`` — is a
**no-op** under FastAPI 0.141: ``include_router`` no longer copies the
child's routes up, it appends one deferred ``_IncludedRouter`` wrapper that
has no ``.path`` at all. The filter kept it, the probe stayed mounted for the
rest of the session, and the first later test to call ``app.openapi()`` blew
up on the probe's unresolvable annotation. That's how
``test_knowledge_loop``/``test_partner_directory``'s
``test_the_endpoint_list_matches_the_router`` came to pass alone and fail in
a full run.

So restore the list itself instead of pattern-matching its contents, and drop
the memoised OpenAPI schema on both edges — ``app.openapi()`` re-generates
only when ``app.router._get_routes_version()`` moves, and that version is a
*sum* that mount+unmount returns to its old value.

Annotation caveat: an endpoint defined inside a test function still gets its
annotations resolved against the **module's** globals (every test module here
is ``from __future__ import annotations``, so they are all strings). Import
anything you annotate with at module level, or FastAPI will treat it as an
unresolved forward ref and turn it into a request-body field.
"""
from __future__ import annotations

from collections.abc import Iterator
from contextlib import contextmanager

from fastapi import APIRouter, FastAPI


@contextmanager
def mounted_router(app: FastAPI, router: APIRouter) -> Iterator[None]:
    """Mount ``router`` on ``app`` for the duration of the block."""
    saved = list(app.router.routes)
    app.include_router(router)
    app.openapi_schema = None
    try:
        yield
    finally:
        app.router.routes[:] = saved
        app.openapi_schema = None


__all__ = ["mounted_router"]