fix(fastapi): Prevent double wrapping of sync handlers on FastAPI >= 0.137

[jhonny-on]

Fixes #6568

What

patch_get_request_handler() wraps dependant.call in a _sentry_call closure and writes it back to the shared dependant object. In FastAPI ≤ 0.136 this was called once per route at registration time, so one wrapper was applied and never repeated. In FastAPI 0.137, include_router() preserves a router tree instead of flattening routes, causing get_request_handler() to be called on every request — so the wrapper count grows by 1 per request, until Python's 1000-frame recursion limit is hit at ~987 requests and the endpoint returns 500 permanently.

Only def (sync) endpoints are affected. async def endpoints go through _sentry_app, not _sentry_call, and are unaffected.

Why the root cause is correct

Test proves it

test_sync_endpoint_does_not_crash_after_many_requests sends 1,000 requests to a sync endpoint registered via include_router() and asserts all return 200. With the bug it fails at request 987; with the fix all 1,000 pass.

Note: the test takes ~75 seconds because it sends 1,000 real requests through TestClient. Happy to discuss a faster approach if the team prefers (e.g. inspecting dependant.call directly, or parameterising the request count).

Would not reccommed to merge this test as-is

Additionally, the diagnosis was confirmed by local reproduction before filing the issue:

• FastAPI 0.137.0 + sentry-sdk 2.35.2, real production app (80+ include_router() calls), 1,200 rapid-fire TestClient requests
• **Crashed at request 987 **
• Time was irrelevant; request count was the trigger
• The same test with FastAPI 0.136.3 runs all 1,200 requests without issue

How

Add a _sentry_is_patched = True sentinel attribute to _sentry_call after wrapping, and check for it before wrapping. If dependant.call is already patched, skip — the _sentry_call still executes on every request (thread/profiling context updates still happen), it just isn't re-wrapped.

# before
dependant.call = _sentry_call

# after
_sentry_call._sentry_is_patched = True
dependant.call = _sentry_call

# and in the guard condition:
and not getattr(dependant.call, "_sentry_is_patched", False)

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Disclosure: This fix was developed with AI assistance (Claude) and has been manually reviewed, reproduced, and verified by a human engineer before submission.