feat: report compatibility evidence

app/main.py

@@ -7,6 +7,7 @@ from fastapi import FastAPI
 from app.api.errors import ApiError, api_error_handler, unhandled_exception_handler
 from app.api.middleware import RequestContextMiddleware
 from app.api.registry import HandlerRegistry, register_contract_routes
+from app.compatibility import build_report
 from app.config import Settings, get_settings
 from app.contracts.model import Snapshot
 from app.lifespan import DatabaseFactory, create_lifespan, default_database_factory
@@ -34,12 +35,19 @@ def create_app(
     app.include_router(health_router)
     if resolved.contract_snapshot is not None:
         snapshot = Snapshot.model_validate_json(resolved.contract_snapshot.read_bytes())
+        resolved_handlers = handlers or HandlerRegistry()
         register_contract_routes(
             app,
             snapshot,
-            handlers or HandlerRegistry(),
+            resolved_handlers,
             resolved.contract_fallback,
         )
+        report = build_report(snapshot, implemented=resolved_handlers.keys())
+
+        @app.get("/admin/compatibility", include_in_schema=False)
+        async def compatibility_report() -> dict[str, object]:
+            return report.as_json()
+
     return app