add test for deeply nested flow deployment.parameters

verifies that deployment.parameters propagates through multiple nesting levels (parent → nested → doubly nested)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: zzstoatzz

tests/runtime/test_deployment.py

@@ -224,3 +224,44 @@ async def parent_flow():
         # Both parent and nested should see the deployment parameters
         assert seen_params["parent"] == {"foo": "from_deployment"}
         assert seen_params["nested"] == {"foo": "from_deployment"}
+
+    async def test_parameters_accessible_in_deeply_nested_flows(
+        self, deployment_id, prefect_client
+    ):
+        """Test that deployment.parameters propagates through multiple nesting levels."""
+        from prefect.flow_engine import run_flow_async
+        from prefect.runtime import deployment as deployment_runtime
+
+        # Track what we saw at each level
+        seen_params = {}
+
+        @flow
+        async def doubly_nested_flow():
+            seen_params["doubly_nested"] = deployment_runtime.parameters
+            return deployment_runtime.parameters
+
+        @flow
+        async def nested_flow():
+            seen_params["nested"] = deployment_runtime.parameters
+            result = await doubly_nested_flow()
+            return result
+
+        @flow
+        async def parent_flow():
+            seen_params["parent"] = deployment_runtime.parameters
+            result = await nested_flow()
+            return result
+
+        # Create flow run from deployment with custom parameters
+        flow_run = await prefect_client.create_flow_run_from_deployment(
+            deployment_id, parameters={"foo": "from_deployment", "level": "deep"}
+        )
+
+        # Execute the flow using the flow engine helper
+        await run_flow_async(parent_flow, flow_run=flow_run)
+
+        # All levels should see the deployment parameters
+        expected = {"foo": "from_deployment", "level": "deep"}
+        assert seen_params["parent"] == expected
+        assert seen_params["nested"] == expected
+        assert seen_params["doubly_nested"] == expected