[codex] Isolate translation langdetect imports on Windows

[tianmind-studio]

Summary

• Add a test-local langdetect fallback for translation optimization tests when the package is missing in lightweight backend environments.
• Restore real utils and models package paths before importing translation modules, so earlier stub-heavy tests cannot make utils.translation or models.transcript_segment unreachable.
• Keep the fallback narrow: it covers the detect, detect_langs, DetectorFactory, and LangDetectException surface used by these tests, and skips itself when the real langdetect package is installed.

Root cause

The translation tests already mock Redis and Google Translate, but they still import utils.translation, which imports langdetect at module load. On this Windows lightweight backend venv, standalone collection failed before the tests could run:

ModuleNotFoundError: No module named 'langdetect'

When collected after stub-heavy tests, a prior lightweight utils package stub could also hide the real backend/utils package, producing:

ModuleNotFoundError: No module named 'utils.translation'

Current status

• Rebased on main at 1a5824403b68ce47c3b0909577cadc1242ba0d3f
• Head refreshed to 3d13fdd672d9a7cb36dc366333f4a5caf6c1deee
• GitHub currently reports the PR as mergeable

Validation

• D:\codex-omi-work\.venvs\omi-backend-vad-refresh\Scripts\python.exe -m pytest backend\tests\unit\test_translation_optimization.py backend\tests\unit\test_translation_cost_optimization.py --collect-only -q --tb=short
  • 175 tests collected
• D:\codex-omi-work\.venvs\omi-backend-vad-refresh\Scripts\python.exe -m pytest backend\tests\unit\test_translation_optimization.py backend\tests\unit\test_translation_cost_optimization.py -q --tb=short
  • 175 passed
• D:\codex-omi-work\.venvs\omi-backend-vad-refresh\Scripts\python.exe -m pytest backend\tests\unit\test_translation_cost_optimization.py backend\tests\unit\test_translation_optimization.py -q --tb=short
  • 175 passed
• D:\codex-omi-work\.venvs\omi-backend-vad-refresh\Scripts\python.exe -m pytest backend\tests\unit\test_action_item_date_validation.py backend\tests\unit\test_translation_optimization.py backend\tests\unit\test_translation_cost_optimization.py -q --tb=short
  • 201 passed
• D:\codex-omi-work\.venvs\omi-backend-vad-refresh\Scripts\python.exe -m py_compile backend\tests\unit\test_translation_optimization.py backend\tests\unit\test_translation_cost_optimization.py
• D:\codex-omi-work\.venvs\omi-backend-vad-refresh\Scripts\python.exe -m black --line-length 120 --skip-string-normalization --check backend\tests\unit\test_translation_optimization.py backend\tests\unit\test_translation_cost_optimization.py
  • 2 files would be left unchanged
• git diff --check origin/main...HEAD
• scripts/pre-commit with the backend Windows venv and local Dart SDK on PATH

[kodjima33]

Test-only stabilization (import isolation / stubs); zero product risk, CI not failing.

[kodjima33]

Test-only stabilization (translation langdetect imports), CI green