Add changelog entry for new behaviour w.r.t subgraph_url

CHANGELOG.md

@@ -115,6 +115,38 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
   Now that Rover supports hot-reloading from `supergraph.yaml` files we've removed the ability to start multiple
   `rover dev` sessions, in multiple terminal windows, and have them communicate with each other.
 
+- **Remove ambiguity around which URL is used for query execution when using `subgraph_url` and `--graph-ref` flag**
+
+  In previous versions of Rover, when the `--graph-ref` flag was used and a subgraph was specified in the 
+  `supergraph.yaml` in the following way, to override a subgraph in Studio:
+
+  ```yaml
+  federation_version: 2.10.0
+  subgraphs:
+    subgraph_a:
+      schema:
+        subgraph_url: "http://localhost:4000/graphql"
+  ```
+  Rover would use the given `subgraph_url` for schema introspection **and** query execution. However, this was a bug in 
+  earlier versions of Rover that has only recently been identified. Now if this same situation occurs, Rover will use
+  the given `subgraph_url` (`http://localhost:4000/graphql` in the example above) for introspection **only**. Query
+  execution will use the `routing_url` from Studio.
+
+  This is consistent with the documented behaviour since this feature launched and in addition is consistent with the 
+  principle that the use of the `supergraph.yaml` will only override `--graph-ref` where you explicitly state that 
+  should happen. To obtain the original behaviour again you simply need to override the `routing_url` in the 
+  `supergraph.yaml` as well, so the example above would become:
+
+  ```yaml
+  federation_version: 2.10.0
+  subgraphs:
+    subgraph_a:
+      routing_url: "http://localhost:4000/graphql"
+      schema:
+        subgraph_url: "http://localhost:4000/graphql"
+  ```
+  and this will use `http://localhost:4000/graphql` for query execution **and** introspection.
+
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