fix(cli): treat agent folder with subfolders as single agent in adk web

When `adk web` is given a path to a single agent directory (containing agent.py or root_agent.yaml), preserve single-agent mode even if that directory contains subfolders.

Fixes #6434

Co-authored-by: Bo Yang <ybo@google.com>
PiperOrigin-RevId: 953470819

Author: boyangsvl

src/google/adk/cli/utils/_nested_agent_loader.py

@@ -30,6 +30,7 @@
 from ...agents.base_agent import BaseAgent
 from ...apps.app import App
 from .agent_loader import AgentLoader
+from .agent_loader import is_single_agent_directory
 from .agent_loader import SPECIAL_AGENTS_DIR
 
 logger = logging.getLogger("google_adk." + __name__)
@@ -41,23 +42,7 @@ class NestedAgentLoader(AgentLoader):
   @staticmethod
   def _is_valid_agent_dir(path: Path) -> bool:
     """Returns True if the directory is a valid agent directory."""
-    if not path.is_dir():
-      return False
-    if (path / "agent.py").is_file():
-      return True
-    if (path / "root_agent.yaml").is_file():
-      return True
-
-    init_py = path / "__init__.py"
-    if init_py.is_file():
-      try:
-        content = init_py.read_text(encoding="utf-8")
-        if "root_agent" in content:
-          return True
-      except Exception as e:
-        logger.warning("Error reading %s: %s", init_py, e)
-
-    return False
+    return is_single_agent_directory(path)
 
   def _has_nested_agents(self, agents_path: Path) -> bool:
     """Returns True if there are any nested agents within the directory (up to max depth)."""
@@ -84,30 +69,37 @@ def _has_nested_agents(self, agents_path: Path) -> bool:
 
   @override
   def _init_agent_mode(self, agents_path: Path) -> None:
-    if agents_path.is_file():
+    try:
+      is_file = agents_path.is_file()
+    except Exception:
+      is_file = False
+
+    if is_file:
       # Explicit file-based single-agent mode
       self._is_single_agent = True
       self._single_agent_name = agents_path.stem
       self.agents_dir = str(agents_path.parent)
+    elif self._is_valid_agent_dir(agents_path):
+      # Single-agent directory mode: treat as single agent even if it has subfolders.
+      self._is_single_agent = True
+      self._single_agent_name = agents_path.name
+      self.agents_dir = str(agents_path.parent)
     else:
-      # It is a directory. Check if it contains any nested agents.
-      if self._has_nested_agents(agents_path):
-        # Force multi-agent (nested) mode even if the root directory itself
-        # contains an agent.py, to allow discovering the nested agents.
-        self._is_single_agent = False
-        self._single_agent_name = None
-        self.agents_dir = str(agents_path)
-      else:
-        # Fall back to parent class behavior
-        super()._init_agent_mode(agents_path)
+      # It is a multi-agent directory containing sub-directories with agents.
+      self._is_single_agent = False
+      self._single_agent_name = None
+      self.agents_dir = str(agents_path)
 
   @override
   def list_agents(self) -> list[str]:
     """Lists all agents recursively across subdirectories (sorted alphabetically)."""
     if self._is_single_agent:
       return [self._single_agent_name]
     base_path = Path(self.agents_dir)
-    if not base_path.exists() or not base_path.is_dir():
+    try:
+      if not base_path.exists() or not base_path.is_dir():
+        return []
+    except Exception:
       return []
 
     apps = []

src/google/adk/cli/utils/agent_loader.py

@@ -42,11 +42,16 @@
 
 def is_single_agent_directory(path: Path | str) -> bool:
   """Returns True if the directory contains a single agent configuration or file."""
-  p = Path(path).resolve()
-  return (
-      p.joinpath("agent.py").is_file()
-      or p.joinpath("root_agent.yaml").is_file()
-  )
+  try:
+    p = Path(path).resolve()
+    if not p.is_dir():
+      return False
+    return (
+        p.joinpath("agent.py").is_file()
+        or p.joinpath("root_agent.yaml").is_file()
+    )
+  except Exception:
+    return False
 
 
 # Special agents directory for agents with names starting with double underscore

tests/unittests/cli/utils/test_nested_agent_loader.py

@@ -58,10 +58,10 @@ def test_list_agents_finds_nested_agents_recursively(self):
       dir2.mkdir(parents=True)
       (dir2 / "root_agent.yaml").write_text("")
 
-      # Create sub_dir/sub_sub_dir/agent_three/__init__.py
+      # Create sub_dir/sub_sub_dir/agent_three/agent.py
       dir3 = temp_path / "sub_dir" / "sub_sub_dir" / "agent_three"
       dir3.mkdir(parents=True)
-      (dir3 / "__init__.py").write_text("root_agent = None")
+      (dir3 / "agent.py").write_text("")
 
       loader = NestedAgentLoader(str(temp_path))
       agents = loader.list_agents()
@@ -102,23 +102,24 @@ def test_list_agents_ignores_hidden_and_special_directories(self):
 
       assert agents == ["valid_agent"]
 
-  def test_list_agents_excludes_root_directory_itself(self):
-    """Root app directory itself is not listed as a nested agent sub-app."""
+  def test_single_agent_directory_with_subfolders_remains_single_agent(self):
+    """A directory with an agent.py at root remains in single-agent mode even with subfolders."""
     with tempfile.TemporaryDirectory() as temp_dir:
-      temp_path = Path(temp_dir)
+      temp_path = Path(temp_dir) / "my_single_agent"
+      temp_path.mkdir()
 
-      # Create agent.py at the root itself
+      # Create agent.py at the root of my_single_agent directory
       (temp_path / "agent.py").write_text("")
 
-      # Create a nested valid agent
+      # Create a nested subfolder containing an agent
       dir_nested = temp_path / "sub_agent"
       dir_nested.mkdir()
       (dir_nested / "agent.py").write_text("")
 
       loader = NestedAgentLoader(str(temp_path))
-      agents = loader.list_agents()
-
-      assert agents == ["sub_agent"]
+      assert loader.is_single_agent is True
+      assert loader.single_agent_name == "my_single_agent"
+      assert loader.list_agents() == ["my_single_agent"]
 
   def test_list_agents_sorts_discovered_agents_alphabetically(self):
     """Returned list of discovered agents is sorted alphabetically."""