fix(genai): resolve blocking I/O in async contexts

[smart-cau]

Description

Fixes blocking I/O errors when using ChatGoogleGenerativeAI in async contexts (e.g., LangGraph applications). The issue occurred because importlib.metadata.version() performs blocking file I/O during async client initialization, which blocks the event loop and triggers BlockingError in async-aware environments.

Solution: Cache package version at module import time instead of reading it on every get_user_agent() call. This eliminates blocking I/O in async contexts while improving performance.

Relevant issues

Fixes #1231

Type

🐛 Bug Fix

Changes

Core Changes

• libs/genai/langchain_google_genai/_common.py
  • Added module-level _LANGCHAIN_GENAI_VERSION cache
  • Modified get_user_agent() to use cached version

Test Changes

• libs/genai/tests/unit_tests/test_common.py
  • Added test_version_is_cached_at_module_level()
  • Added test_get_user_agent_no_blocking_in_async_context()
  • Added test_async_context_execution()
  • Updated existing tests to use cached version

Testing

Unit Tests

• ✅ All existing unit tests pass in libs/genai
• ✅ New tests verify version caching behavior
• ✅ New tests ensure no blocking I/O in async contexts

Integration Testing

• ✅ Tested with LangGraph minimal reproducible example from issue BlockingError when using ChatGoogleGenerativeAI with async in LangGraph dev #1231
• ✅ Confirmed BlockingError no longer occurs

Test Commands Run

cd libs/genai && make test

Note

This PR is part of the fix for issue #1231. A companion PR (#1267) addresses the same issue in langchain-google-vertexai (related to #873).

The solution:

• ✅ No breaking changes to public APIs
• ✅ Backward compatible
• ✅ Performance improvement (version read only once)
• ✅ Zero overhead for subsequent calls
• ✅ Safe in all contexts (sync and async)

[lkuligin]

could you split the PR into two parts, one touching genai and another touching vertexai, please?

[smart-cau]

could you split the PR into two parts, one touching genai and another touching vertexai, please?

Done! @lkuligin I've split this PR into two separate PRs as requested:

• This PR now only touches genai package
• Created #1267 for vertexai package with the same fix

Both PRs address the same blocking I/O issue in async contexts.