Add ability to attach rules as context (#29109)

Release Notes:

- agent: Added support for adding rules as context.

crates/agent/src/thread.rs

@@ -774,7 +774,9 @@ impl Thread {
                                 cx,
                             );
                         }
-                        AssistantContext::FetchedUrl(_) | AssistantContext::Thread(_) => {}
+                        AssistantContext::FetchedUrl(_)
+                        | AssistantContext::Thread(_)
+                        | AssistantContext::Rules(_) => {}
                     }
                 }
             });