[codex] Isolate sync decode test imports on Windows

[tianmind-studio]

Summary

• Add a temporary python_multipart stub while importing routers.sync in the PCM and Opus decode unit tests, so lightweight Windows backend envs can collect the tests without the full multipart package installed.
• Ensure the tests' existing import-time stubs expose the full routers.sync import surface, even when earlier-collected tests left partial modules in sys.modules.
• Keep the changes scoped to test isolation; production sync decode code is unchanged.

Root cause

These decode tests exercise pure PCM/Opus WAL conversion helpers, but importing routers.sync also builds FastAPI routes and imports optional service helpers. In this Windows lightweight backend venv, standalone collection failed on FastAPI's multipart package check. In collection-order runs after stub-heavy tests, partial opuslib, database.conversations, utils.cloud_tasks, and utils.other.endpoints modules could block collection before the decode assertions ran.

A later local stacked Windows collect scan found two remaining same-process cases after the first pass: prior tests could leave models.conversation_enums.ConversationSource without the omi / limitless members, or leave utils.executors without the full import surface used by routers.sync. This PR now fills those stubs before importing routers.sync.

Before this change:

• python -m pytest backend\tests\unit\test_sync_pcm_decode.py --collect-only -q --tb=short -> RuntimeError: Form data requires "python-multipart" to be installed.
• python -m pytest backend\tests\unit\test_sync_opus_decode.py --collect-only -q --tb=short -> RuntimeError: Form data requires "python-multipart" to be installed.
• python -m pytest backend\tests\unit\test_action_item_date_validation.py backend\tests\unit\test_sync_pcm_decode.py backend\tests\unit\test_sync_opus_decode.py --collect-only -q --tb=short --continue-on-collection-errors -> import failures from partial sync dependencies.

Current status

• Rebased on main at 1a5824403b68ce47c3b0909577cadc1242ba0d3f
• Head refreshed to 8c31bedb161584d24ff93530717abeba17825a0b
• GitHub currently reports the PR as mergeable
• GitHub Actions Lint Check run 27684277856 completed successfully on this head

Validation

• D:\codex-omi-work\.venvs\omi-backend-vad-refresh\Scripts\python.exe -m pytest backend\tests\unit\test_realtime_integrations_usage_tracking.py backend\tests\unit\test_sync_pcm_decode.py backend\tests\unit\test_sync_opus_decode.py --collect-only -q --tb=short --continue-on-collection-errors
  • 48 tests collected, 1 warning
• D:\codex-omi-work\.venvs\omi-backend-vad-refresh\Scripts\python.exe -m pytest backend\tests\unit\test_sync_pcm_decode.py backend\tests\unit\test_sync_opus_decode.py -q --tb=short
  • 44 passed, 1 warning
• D:\codex-omi-work\.venvs\omi-backend-vad-refresh\Scripts\python.exe -m pytest backend\tests\unit\test_sync_opus_decode.py backend\tests\unit\test_sync_pcm_decode.py -q --tb=short
  • 44 passed, 1 warning
• 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_sync_pcm_decode.py backend\tests\unit\test_sync_opus_decode.py -q --tb=short
  • 70 passed, 1 warning
• 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_sync_opus_decode.py backend\tests\unit\test_sync_pcm_decode.py -q --tb=short
  • 70 passed, 1 warning
• D:\codex-omi-work\.venvs\omi-backend-vad-refresh\Scripts\python.exe -m py_compile backend\tests\unit\test_sync_pcm_decode.py backend\tests\unit\test_sync_opus_decode.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_sync_pcm_decode.py backend\tests\unit\test_sync_opus_decode.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

Stacked Windows collect check

On a local-only integration branch containing the open Windows collect-isolation PR heads, D:\codex-omi-work\.venvs\omi-backend-vad-refresh\Scripts\python.exe -m pytest backend\tests\unit --collect-only -q --tb=short --continue-on-collection-errors now exits 0 with 4206 tests collected.

[kodjima33]

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

[kodjima33]

Test-only stabilization (sync decode test imports), CI green