fix(cli): Discover newly staged agents during validation

[yousefalbanna1]

Problem:

_validate_agent_import() can fail to import a newly created agent package when Python has already cached the contents of the package's parent directory.

In that case, the package and agent.py exist, but importlib.import_module() can still raise ModuleNotFoundError.

Solution:

Invalidate Python's import caches immediately before importing the agent package.

A regression test was added that primes the import cache before creating the package and verifies that validation can still discover the new agent.

Testing Plan

Unit Tests:

• I have added unit tests for my change.

• All unit tests pass locally.

• python -m pytest tests/unittests/cli/utils/test_cli_deploy.py::TestValidateAgentImport -q — 12 passed.

• python -m pytest tests/unittests/cli/utils/test_cli_deploy.py -q — 98 passed.

• tox:

  • Python 3.10 — passed.
  • Python 3.11 — passed.
  • Python 3.12 — 2 failures in tests/unittests/test_import_loading.py.
  • Python 3.13 — passed.
  • Python 3.14 — passed.

• The same two Python 3.12 failures reproduce on the unmodified base commit 6eb1d35d.

• Pre-commit checks for the changed files — passed.

Manual End-to-End (E2E) Tests:

Built the package with uv build, installed the generated wheel in a clean virtual environment, and verified that ADK imports successfully and the updated validation code is present.

A cloud deployment was not performed.

Additional context

The two Python 3.12 tox failures are unrelated to this change and reproduce on the unmodified base commit.