fix: new agent card

[racinmat]

Fixes #2622.
Basically reflects the change from https://github.com/a2aproject/a2a-python/releases/tag/v0.3.0.

testing plan

I ran the relevant tests to my code and here are the results, everything passes except few tests that are completely unrelated.

pytest .\tests\unittests\cli\                                                                                                                                                                          
======================================================================================================================= test session starts =======================================================================================================================
platform win32 -- Python 3.12.8, pytest-8.4.1, pluggy-1.6.0
rootdir: C:\Projects\others\adk-python
configfile: pyproject.toml
plugins: anyio-4.9.0, langsmith-0.3.45, asyncio-1.1.0, mock-3.14.1, xdist-3.8.0
asyncio: mode=Mode.AUTO, asyncio_default_fixture_loop_scope=function, asyncio_default_test_loop_scope=function
collected 222 items                                                                                                                                                                                                                                                

tests\unittests\cli\test_cli_tools_click_option_mismatch.py ................                                                                                                                                                                                 [  7%] 
tests\unittests\cli\test_fast_api.py ................................                                                                                                                                                                                        [ 21%]
tests\unittests\cli\utils\test_agent_loader.py ..................................                                                                                                                                                                            [ 36%]
tests\unittests\cli\utils\test_cli.py ........                                                                                                                                                                                                               [ 40%]
tests\unittests\cli\utils\test_cli_create.py ..................................                                                                                                                                                                              [ 55%]
tests\unittests\cli\utils\test_cli_deploy.py ..........................................                                                                                                                                                                      [ 74%] 
tests\unittests\cli\utils\test_cli_tools_click.py ......FF..................FF..                                                                                                                                                                             [ 88%] 
tests\unittests\cli\utils\test_evals.py ..........................                                                                                                                                                                                           [100%]

pytest .\tests\unittests\agents\
======================================================================================================================= test session starts =======================================================================================================================
platform win32 -- Python 3.12.8, pytest-8.4.1, pluggy-1.6.0
rootdir: C:\Projects\others\adk-python
configfile: pyproject.toml
plugins: anyio-4.9.0, langsmith-0.3.45, asyncio-1.1.0, mock-3.14.1, xdist-3.8.0
asyncio: mode=Mode.AUTO, asyncio_default_fixture_loop_scope=function, asyncio_default_test_loop_scope=function
collected 342 items                                                                                                                                                                                                                                                

tests\unittests\agents\test_agent_clone.py ..............................                                                                                                                                                                                    [  8%]
tests\unittests\agents\test_agent_config.py ............                                                                                                                                                                                                     [ 12%] 
tests\unittests\agents\test_base_agent.py ........................................................                                                                                                                                                           [ 28%] 
tests\unittests\agents\test_callback_context.py ..................................                                                                                                                                                                           [ 38%] 
tests\unittests\agents\test_langgraph_agent.py ......                                                                                                                                                                                                        [ 40%]
tests\unittests\agents\test_live_request_queue.py ..........                                                                                                                                                                                                 [ 43%] 
tests\unittests\agents\test_llm_agent_callbacks.py ............                                                                                                                                                                                              [ 46%] 
tests\unittests\agents\test_llm_agent_fields.py ......................................                                                                                                                                                                       [ 57%] 
tests\unittests\agents\test_llm_agent_include_contents.py ......                                                                                                                                                                                             [ 59%] 
tests\unittests\agents\test_llm_agent_output_save.py ..........................                                                                                                                                                                              [ 67%] 
tests\unittests\agents\test_loop_agent.py ....                                                                                                                                                                                                               [ 68%] 
tests\unittests\agents\test_model_callback_chain.py ............                                                                                                                                                                                             [ 71%] 
tests\unittests\agents\test_parallel_agent.py ....                                                                                                                                                                                                           [ 73%]
tests\unittests\agents\test_readonly_context.py ......                                                                                                                                                                                                       [ 74%] 
tests\unittests\agents\test_remote_a2a_agent.py ..........................................................................                                                                                                                                   [ 96%] 
tests\unittests\agents\test_run_config.py ........                                                                                                                                                                                                           [ 98%] 
tests\unittests\agents\test_sequential_agent.py ....                                                                                                                                                                                                         [100%]

The errors are completely unrelated, they are caused by <Result OSError(22, 'A required privilege is not held by the client')>.exit_code because I run tests on windows and nobody bothered to make them fully multiplatform.

[gemini-code-assist]

Summary of Changes

Hello @racinmat, 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 introduces an update to the agent configuration file naming convention, transitioning from agent.json to agent-card.json. The primary goal is to align with recent changes in the a2a-python project, ensuring consistency across related components. The changes include renaming existing sample agent configuration files and modifying the agent loading logic to support both the new and old naming conventions, providing a smooth transition path. This update ensures that the system correctly identifies and loads agent configurations while maintaining compatibility with previous versions.

Highlights

• Agent Card Naming Convention: The standard agent configuration file name has been updated from agent.json to agent-card.json across all sample directories, reflecting a new naming convention.
• Backward Compatibility: The agent loading mechanism has been enhanced to first look for agent-card.json and then gracefully fall back to agent.json, ensuring backward compatibility for existing configurations.
• Test Suite Updates: Unit tests for remote A2A agents and FastAPI integration have been updated to align with the new agent-card.json naming, ensuring test accuracy and consistency with the updated logic.

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[gemini-code-assist]

Code Review

This pull request updates the codebase to prefer agent-card.json over the deprecated agent.json for agent definitions, aligning with a change in a2a-python. The changes correctly implement backward compatibility by checking for both filenames. The sample agent files and tests have been updated accordingly. My review includes one suggestion to refactor a loop in src/google/adk/cli/fast_api.py to improve efficiency and maintainability by removing a redundant file system check.