test: assert OPTIONS-preflight test matches at least one route

Greptile flagged a vacuous-pass risk: the loop only asserts inside the
match branch, so if no route matched the scope the test would pass even
on a broken FastAPI version. Count matches and assert matched > 0.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: declan-scale

agentex/tests/unit/api/test_otel_route_compat.py

@@ -49,7 +49,14 @@ def test_options_preflight_route_matching_does_not_crash(self):
             "path": "/agents",
             "headers": [],
         }
+        matched = 0
         for route in fastapi_app.routes:
             match, _ = route.matches(scope)
             if match in (Match.FULL, Match.PARTIAL):
+                matched += 1
                 assert route.path is not None
+        assert matched > 0, (
+            "No route matched the OPTIONS /agents preflight scope, so the "
+            "`.path` assertion never ran. The test would pass vacuously even "
+            "on a broken FastAPI version. Pick a path served by app.routes."
+        )