fix: Handle App objects in eval and graph endpoints

[ejfn]

Description

Fixes #3059

This PR fixes two endpoints in adk web that fail when using App objects instead of bare agents.

Changes

• Eval execution endpoint (line ~969): Extract root_agent from App objects before passing to LocalEvalService
• Graph visualization endpoint (line ~1308): Extract root_agent from App objects before graph operations

Both endpoints now properly handle both BaseAgent and App objects by checking the type and extracting .root_agent when needed.

Testing Plan

Manual E2E Testing with ADK Web

Tested with an App object that includes context caching:

from google.adk.apps import App
from google.adk.agents import LlmAgent

root_agent = LlmAgent(name="MyAgent", model="gemini-1.5-pro-002")
app = App(
    name="my_agent",
    root_agent=root_agent,
    context_cache_config=ContextCacheConfig(...)
)

Before fix:

• Graph visualization failed (tried to call agent methods on App object)
• Eval execution failed (LocalEvalService received App instead of agent)

After fix:

• Graph visualization works correctly
• Eval execution works correctly
• Both endpoints properly extract root_agent from App objects

Checklist

• Code follows project style (autoformat.sh passed)
• Changes are focused and minimal
• Issue adk web: Multiple endpoints fail with App objects #3059 created and referenced
• Manual E2E testing completed

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[gemini-code-assist]

Summary of Changes

Hello @ejfn, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical compatibility issue within the adk web tool, specifically concerning its eval and graph endpoints. Previously, these functionalities would fail when interacting with App objects, expecting BaseAgent instances instead. The changes introduce robust type checking and extraction logic, ensuring that the underlying root_agent is correctly identified and utilized, thereby enabling seamless operation with both BaseAgent and App objects across the affected endpoints.

Highlights

• App Object Compatibility: The pull request resolves an issue where adk web endpoints failed when App objects were used instead of bare agents, ensuring proper handling for both.
• Eval Execution Endpoint Fix: The run_eval endpoint now correctly extracts the root_agent from App objects before passing them to the LocalEvalService.
• Graph Visualization Endpoint Fix: The get_event_graph endpoint has been updated to extract the root_agent from App objects, allowing graph operations to proceed without errors.

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[gemini-code-assist]

Code Review

This pull request correctly addresses an issue where App objects were not handled correctly in the run_eval and get_event_graph endpoints. The fix involves checking if the loaded object is an App and extracting its root_agent property. While the logic is correct, it introduces code duplication. My feedback suggests refactoring this repeated logic into a private helper method to improve maintainability.