fix(tests): order-independence pin for S7 migration preflight (#763)

[dolho]

Summary

4 tests in tests/git-sync/test_s7_reserve_instance_id.py::TestMigrationPreflight fail in the full integration suite but pass in isolation. Root cause is a sys.modules pollution + reimport ordering bug. Fixed in tests/git-sync/conftest.py with an autouse pin that restores the real utils.helpers and evicts the cached db.* subtree before every git-sync test.

Related to #763.

Root cause

tests/test_validation.py:35 and tests/test_watchdog_unit.py:54 execute, at module import time:

sys.modules["utils.helpers"] = _helpers_mod

The stub has utc_now / utc_now_iso / to_utc_iso / parse_iso_timestamp — but no iso_cutoff. The top-level tests/conftest.py preload installs the real utils.helpers first, but either polluter overwrites it permanently when collected ahead of tests/git-sync/.

TestMigrationPreflight then does:

sys.modules.pop("db.migrations", None)
from db.migrations import _find_duplicate_working_branches

The reimport chain hits db/__init__.py → db/schedules.py → from utils.helpers import iso_cutoff, ... → ImportError, surfaced by the test as pytest.fail("S7 migration helper ... is missing").

Verified by reproducing the exact ImportError outside pytest with python -c "...install stub then reimport db.migrations...".

Fix

Per the issue's recommendation, an order-independence pin in tests/git-sync/conftest.py:

1. Autouse fixture restores the real utils.helpers if the current sys.modules entry lacks iso_cutoff (the discriminator for the stub).
2. Same fixture evicts cached db / db.* modules so the next from db.migrations import … reloads db/__init__.py and db/schedules.py against the restored real utils.helpers.

Both steps are idempotent (no-op when state is already clean), cheap, and run before every git-sync test. Integration-tier counterpart to the unit-tier pin added by #714.

Test plan

• test_s7_reserve_instance_id.py::TestMigrationPreflight passes in isolation — 4 passed
• test_validation.py → test_s7 passes — 23 passed, 3 skipped (was 4 failures pre-fix)
• test_watchdog_unit.py → test_s7 passes — 39 passed
• Full test_s7_reserve_instance_id.py still passes — 12 passed
• test_validation.py / test_watchdog_unit.py collection errors are pre-existing and unrelated (verified via git stash)
• Reviewer pass

Files

File	Change
tests/git-sync/conftest.py	+68 lines: _restore_real_utils_helpers() and _evict_db_module_cache() helpers + autouse _pin_module_state_for_db_reimports fixture

🤖 Generated with Claude Code

[vybe]

LGTM — clean, minimal test infra fix. Root cause well-documented, fix is idempotent and correctly scoped to git-sync/.