chore: WIP endpoint

PiperOrigin-RevId: 788232652

Author: wyf7107

src/google/adk/cli/fast_api.py

@@ -277,20 +277,32 @@ async def builder_build(files: list[UploadFile]) -> bool:
       response_model_exclude_none=True,
       response_class=PlainTextResponse,
   )
-  async def get_agent_builder(app_name: str):
+  async def get_agent_builder(app_name: str, file_path: Optional[str] = None):
     base_path = Path.cwd() / agents_dir
     agent_dir = base_path / app_name
-    file_name = "root_agent.yaml"
-    file_path = agent_dir / file_name
-    if not file_path.is_file():
-      return ""
+    if not file_path:
+      file_name = "root_agent.yaml"
+      root_file_path = agent_dir / file_name
+      if not root_file_path.is_file():
+        return ""
+      else:
+        return FileResponse(
+            path=root_file_path,
+            media_type="application/x-yaml",
+            filename="${app_name}.yaml",
+            headers={"Cache-Control": "no-store"},
+        )
     else:
-      return FileResponse(
-          path=file_path,
-          media_type="application/x-yaml",
-          filename="${app_name}.yaml",
-          headers={"Cache-Control": "no-store"},
-      )
+      agent_file_path = agent_dir / file_path
+      if not agent_file_path.is_file():
+        return ""
+      else:
+        return FileResponse(
+            path=agent_file_path,
+            media_type="application/x-yaml",
+            filename=file_path,
+            headers={"Cache-Control": "no-store"},
+        )
 
   if a2a:
     try: