feat: add .yml file extension support for agent file watcher

[yamadashy]

Summary

Add .yml extension to the watched file extensions in AgentChangeEventHandler.on_modified() alongside .py and .yaml files.

This allows the --reload_agents flag to properly detect changes in .yml configuration files.

Fixes #3834

Scope

This PR only adds .yml to the file watcher for hot reload. It does not add support for root_agent.yml as an agent definition file (that would require changes to AgentLoader and could be addressed in a separate PR if needed).

Testing Plan

• Manual testing: Run adk web --reload_agents, modify a .yml file in the agent directory, and verify the reload is triggered

Note: This PR is marked as draft because the approach hasn't been confirmed in the issue yet. Please let me know if this direction works for you.

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[gemini-code-assist]

Summary of Changes

Hello @yamadashy, 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 enhances the agent file watcher to recognize .yml file extensions, alongside existing .py and .yaml extensions. This ensures that any changes made to .yml configuration files will properly trigger a hot reload when the --reload_agents flag is active, addressing a previous limitation where these files were not being monitored for modifications.

Highlights

• New File Extension Support: Added .yml to the list of file extensions watched by the AgentChangeEventHandler.
• Hot Reload Functionality: This change enables the --reload_agents flag to correctly detect and respond to modifications in .yml configuration files.

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[gemini-code-assist]

Code Review

This pull request adds support for the .yml file extension to the agent file watcher for hot reloading. While the change is a good first step, I've suggested a small refactoring for better readability. More critically, the agent loading logic in AgentLoader doesn't seem to support .yml files, which will likely cause reloads to fail. This needs to be addressed to make the feature work as intended. Please see my detailed comments for specifics.

[gemini-code-assist]

While this change correctly adds .yml to the file watcher for hot reloading, the underlying AgentLoader in src/google/adk/cli/utils/agent_loader.py does not appear to support loading agents from .yml files. Functions like _load_from_yaml_config and _determine_agent_language specifically look for root_agent.yaml. This discrepancy will likely cause reloads triggered by .yml file changes to fail. To fully implement this feature, the agent loading logic should also be updated to recognize and load .yml configuration files.

[gemini-code-assist]

The chain of or conditions can be made more concise and maintainable. The endswith() string method can accept a tuple of suffixes to check against, which is a more Pythonic way to handle this.

Suggested change

	if not (event.src_path.endswith(".py") or event.src_path.endswith(".yaml") or event.src_path.endswith(".yml")):
	if not event.src_path.endswith(('.py', '.yaml', '.yml')):

[adk-bot]

Response from ADK Triaging Agent

Hello @yamadashy, thank you for your contribution!

To help reviewers evaluate your changes, could you please add a testing plan section to your pull request description? This section should detail how you've tested the changes to ensure the agent file watcher correctly reloads on .yml file modifications.

Additionally, it appears the CLA (Contributor License Agreement) check has failed. Please ensure you have signed the CLA, as we cannot merge this pull request until that is complete.

Thank you!