story-kit: merge 176_bug_stories_moved_to_current_get_supervisor_instead_of_coder

server/src/http/mcp.rs

@@ -442,7 +442,7 @@ fn handle_tools_list(id: Option<Value>) -> JsonRpcResponse {
                             },
                             "agent_name": {
                                 "type": "string",
-                                "description": "Agent name from project.toml config. If omitted, uses the first configured agent."
+                                "description": "Agent name from project.toml config. If omitted, uses the first coder agent (stage = \"coder\"). Supervisor must be requested explicitly by name."
                             }
                         },
                         "required": ["story_id"]
@@ -2890,6 +2890,71 @@ mod tests {
         assert!(result.unwrap_err().contains("story_id"));
     }
 
+    #[tokio::test]
+    async fn tool_start_agent_no_agent_name_no_coder_returns_clear_error() {
+        // Config has only a supervisor — start_agent without agent_name should
+        // refuse rather than silently assigning supervisor.
+        let tmp = tempfile::tempdir().unwrap();
+        let sk = tmp.path().join(".story_kit");
+        std::fs::create_dir_all(&sk).unwrap();
+        std::fs::write(
+            sk.join("project.toml"),
+            r#"
+[[agent]]
+name = "supervisor"
+stage = "other"
+"#,
+        )
+        .unwrap();
+        let ctx = test_ctx(tmp.path());
+        let result = tool_start_agent(&json!({"story_id": "42_my_story"}), &ctx).await;
+        assert!(result.is_err());
+        let err = result.unwrap_err();
+        assert!(
+            err.contains("coder"),
+            "error should mention 'coder', got: {err}"
+        );
+    }
+
+    #[tokio::test]
+    async fn tool_start_agent_no_agent_name_picks_coder_not_supervisor() {
+        // Config has supervisor first, then coder-1. Without agent_name the
+        // coder should be selected, not supervisor. The call will fail due to
+        // missing git repo / worktree, but the error must NOT be about
+        // "No coder agent configured".
+        let tmp = tempfile::tempdir().unwrap();
+        let sk = tmp.path().join(".story_kit");
+        std::fs::create_dir_all(&sk).unwrap();
+        std::fs::write(
+            sk.join("project.toml"),
+            r#"
+[[agent]]
+name = "supervisor"
+stage = "other"
+
+[[agent]]
+name = "coder-1"
+stage = "coder"
+"#,
+        )
+        .unwrap();
+        let ctx = test_ctx(tmp.path());
+        let result = tool_start_agent(&json!({"story_id": "42_my_story"}), &ctx).await;
+        // May succeed or fail for infrastructure reasons (no git repo), but
+        // must NOT fail with "No coder agent configured".
+        if let Err(err) = result {
+            assert!(
+                !err.contains("No coder agent configured"),
+                "should not fail on agent selection, got: {err}"
+            );
+            // Should also not complain about supervisor being absent.
+            assert!(
+                !err.contains("supervisor"),
+                "should not select supervisor, got: {err}"
+            );
+        }
+    }
+
     #[tokio::test]
     async fn tool_create_worktree_missing_story_id() {
         let tmp = tempfile::tempdir().unwrap();