fix(eval): support get_agent_async in adk eval

Merge google#4413

**Please ensure you have read the [contribution guide](https://github.com/google/adk-python/blob/main/CONTRIBUTING.md) before creating a pull request.**

### Link to Issue or Description of Change

**1. Link to an existing issue (if applicable):**

- Related: google#4410

**Problem:**
`adk eval` only resolved `agent.root_agent`, while `AgentEvaluator` supports both `root_agent` and `get_agent_async`. This inconsistency caused valid agent modules (for `AgentEvaluator`) to fail in CLI evaluation.

**Solution:**
Aligned `adk eval` agent resolution with `AgentEvaluator` by updating CLI loading logic to support both entry points:
- `root_agent`
- `get_agent_async`

Implementation details:
- Made `get_root_agent` in `cli_eval.py` asynchronous and added fallback resolution to `get_agent_async`.
- Updated `cli_tools_click.py` to call `get_root_agent` via `asyncio.run(...)`.
- Added/updated unit tests for both resolution paths and the error path when neither is present.

### Testing Plan

**Unit Tests:**

- [x] I have added or updated unit tests for my change.
- [x] All unit tests pass locally.

```
% pytest tests/unittests/cli

========================= 271 passed, 140 warnings in 7.69s =========================
```

**Manual End-to-End (E2E) Tests:**

No manual E2E test was run for this PR.

### Checklist

- [x] I have read the [CONTRIBUTING.md](https://github.com/google/adk-python/blob/main/CONTRIBUTING.md) document.
- [x] I have performed a self-review of my own code.
- [x] I have commented my code, particularly in hard-to-understand areas.
- [x] I have added tests that prove my fix is effective or that my feature works.
- [x] New and existing unit tests pass locally with my changes.
- [ ] I have manually tested my changes end-to-end.
- [x] Any dependent changes have been merged and published in downstream modules.

### Additional context

This PR focuses on one scoped item from google#4410: agent resolution parity between `adk eval` and `AgentEvaluator` (`root_agent` / `get_agent_async`).

Co-authored-by: George Weale <gweale@google.com>
COPYBARA_INTEGRATE_REVIEW=google#4413 from ftnext:adk-eval-get-agent-async 267c196
PiperOrigin-RevId: 952361014

Author: 2 people

src/google/adk/cli/cli_eval.py

@@ -26,7 +26,7 @@
 import click
 from google.genai import types as genai_types
 
-from ..agents.llm_agent import Agent
+from ..agents.base_agent import BaseAgent
 from ..evaluation.base_eval_service import BaseEvalService
 from ..evaluation.base_eval_service import EvaluateConfig
 from ..evaluation.base_eval_service import EvaluateRequest
@@ -74,11 +74,18 @@ def _get_agent_module(agent_module_file_path: str) -> ModuleType:
   return _import_from_path(module_name, file_path)
 
 
-def get_root_agent(agent_module_file_path: str) -> Agent:
+async def get_root_agent(agent_module_file_path: str) -> BaseAgent:
   """Returns root agent given the agent module."""
   agent_module = _get_agent_module(agent_module_file_path)
-  root_agent = agent_module.agent.root_agent
-  return cast(Agent, root_agent)
+  agent_module_with_agent = getattr(agent_module, "agent", agent_module)
+  if hasattr(agent_module_with_agent, "root_agent"):
+    return cast(BaseAgent, agent_module_with_agent.root_agent)
+  elif hasattr(agent_module_with_agent, "get_agent_async"):
+    root_agent, _ = await agent_module_with_agent.get_agent_async()
+    return cast(BaseAgent, root_agent)
+  raise ValueError(
+      "Agent module should have either `root_agent` or `get_agent_async`."
+  )
 
 
 def try_get_reset_func(agent_module_file_path: str) -> Any:

src/google/adk/cli/cli_tools_click.py

@@ -26,7 +26,9 @@
 import sys
 import tempfile
 import textwrap
+from typing import cast
 from typing import Optional
+from typing import TYPE_CHECKING
 
 import click
 from click.core import ParameterSource
@@ -42,6 +44,9 @@
 from .utils import envs
 from .utils import logs
 
+if TYPE_CHECKING:
+  from ..agents.llm_agent import LlmAgent
+
 LOG_LEVELS = click.Choice(
     ["DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL"],
     case_sensitive=False,
@@ -1027,7 +1032,7 @@ def cli_eval(
   print(f"Using evaluation criteria: {eval_config}")
   eval_metrics = get_eval_metrics_from_config(eval_config)
 
-  root_agent = get_root_agent(agent_module_file_path)
+  root_agent = asyncio.run(get_root_agent(agent_module_file_path))
   app_name = os.path.basename(agent_module_file_path)
   agents_dir = os.path.dirname(agent_module_file_path)
   eval_sets_manager = None
@@ -1257,7 +1262,7 @@ def cli_optimize(
   else:
     optimizer_config = GEPARootAgentPromptOptimizerConfig()
 
-  root_agent = get_root_agent(agent_module_file_path)
+  root_agent = asyncio.run(get_root_agent(agent_module_file_path))
   app_name = os.path.basename(agent_module_file_path)
   agents_dir = os.path.dirname(agent_module_file_path)
   if app_name != sampler_config.app_name:
@@ -1270,7 +1275,9 @@ def cli_optimize(
   sampler = LocalEvalSampler(sampler_config, eval_sets_manager)
   optimizer = GEPARootAgentPromptOptimizer(optimizer_config)
 
-  optimization_result = asyncio.run(optimizer.optimize(root_agent, sampler))
+  optimization_result = asyncio.run(
+      optimizer.optimize(cast("LlmAgent", root_agent), sampler)
+  )
   best_idx = optimization_result.gepa_result["best_idx"]
 
   click.echo("=" * 80)
@@ -1483,7 +1490,7 @@ def cli_generate_eval_cases(
 
   try:
     eval_sets_manager = get_eval_sets_manager(eval_storage_uri, agents_dir)
-    root_agent = get_root_agent(agent_module_file_path)
+    root_agent = asyncio.run(get_root_agent(agent_module_file_path))
 
     # Try to create if it doesn't already exist.
     if (

tests/unittests/cli/utils/test_cli_eval.py

@@ -19,6 +19,7 @@
 from types import SimpleNamespace
 from unittest import mock
 
+from google.adk.cli.cli_eval import get_root_agent
 import pytest
 
 
@@ -110,3 +111,40 @@ def test_get_eval_sets_manager_gcs(monkeypatch):
   )
   assert manager == mock_gcs_manager
   mock_create_gcs.assert_called_once_with("gs://bucket")
+
+
+@pytest.mark.asyncio
+async def test_get_root_agent_supports_root_agent(monkeypatch):
+  root_agent = mock.MagicMock()
+  agent_module = SimpleNamespace(agent=SimpleNamespace(root_agent=root_agent))
+  monkeypatch.setattr(
+      "google.adk.cli.cli_eval._get_agent_module",
+      lambda _agent_module_file_path: agent_module,
+  )
+  assert await get_root_agent("some/dir") == root_agent
+
+
+@pytest.mark.asyncio
+async def test_get_root_agent_supports_get_agent_async(monkeypatch):
+  root_agent = mock.MagicMock()
+  get_agent_async = mock.AsyncMock(return_value=(root_agent, object()))
+  agent_module = SimpleNamespace(
+      agent=SimpleNamespace(get_agent_async=get_agent_async)
+  )
+  monkeypatch.setattr(
+      "google.adk.cli.cli_eval._get_agent_module",
+      lambda _agent_module_file_path: agent_module,
+  )
+  assert await get_root_agent("some/dir") == root_agent
+  get_agent_async.assert_awaited_once()
+
+
+@pytest.mark.asyncio
+async def test_get_root_agent_raises_without_supported_entrypoint(monkeypatch):
+  agent_module = SimpleNamespace(agent=SimpleNamespace())
+  monkeypatch.setattr(
+      "google.adk.cli.cli_eval._get_agent_module",
+      lambda _agent_module_file_path: agent_module,
+  )
+  with pytest.raises(ValueError, match="root_agent|get_agent_async"):
+    await get_root_agent("some/dir")

tests/unittests/cli/utils/test_cli_tools_click.py

@@ -61,7 +61,9 @@ def mock_load_eval_set_from_file():
 
 @pytest.fixture
 def mock_get_root_agent():
-  with mock.patch("google.adk.cli.cli_eval.get_root_agent") as mock_func:
+  with mock.patch(
+      "google.adk.cli.cli_eval.get_root_agent", new_callable=mock.AsyncMock
+  ) as mock_func:
     mock_func.return_value = root_agent
     yield mock_func