fix: properly return errors for malformed config (#2027)

crates/goose-server/src/routes/config_management.rs

@@ -185,7 +185,17 @@ pub async fn get_extensions(
 
     match ExtensionManager::get_all() {
         Ok(extensions) => Ok(Json(ExtensionResponse { extensions })),
-        Err(_) => Err(StatusCode::INTERNAL_SERVER_ERROR),
+        Err(err) => {
+            // Return UNPROCESSABLE_ENTITY only for DeserializeError, INTERNAL_SERVER_ERROR for everything else
+            if err
+                .downcast_ref::<goose::config::base::ConfigError>()
+                .is_some_and(|e| matches!(e, goose::config::base::ConfigError::DeserializeError(_)))
+            {
+                Err(StatusCode::UNPROCESSABLE_ENTITY)
+            } else {
+                Err(StatusCode::INTERNAL_SERVER_ERROR)
+            }
+        }
     }
 }
 
@@ -196,6 +206,7 @@ pub async fn get_extensions(
     responses(
         (status = 200, description = "Extension added or updated successfully", body = String),
         (status = 400, description = "Invalid request"),
+        (status = 422, description = "Could not serialize config.yaml"),
         (status = 500, description = "Internal server error")
     )
 )]