Run transport security tests in process instead of over sockets

src/mcp/server/streamable_http.py

@@ -669,7 +669,7 @@ async def _handle_get_request(self, request: Request, send: Send) -> None:
             await response(request.scope, request.receive, send)
             return
 
-        if not await self._validate_request_headers(request, send):  # pragma: no cover
+        if not await self._validate_request_headers(request, send):
             return
 
         # Handle resumability: check for Last-Event-ID header

tests/interaction/transports/__init__.py

@@ -0,0 +1,9 @@
+"""Transport-specific interaction tests, and the in-process streaming bridge they are built on.
+
+`StreamingASGITransport` is re-exported here as the sanctioned import point for test code
+outside this suite (the bridge module itself is suite-private).
+"""
+
+from tests.interaction.transports._bridge import StreamingASGITransport
+
+__all__ = ["StreamingASGITransport"]