The test passed overlay and sampling as separate objects while production
aliases them, so an in-place mutation slipped through it. Also syncs the
telemetry schema page and adds the missing postgres round-trip assertion.
The fixture used to DROP the shared llm_calls table on every run, wiping
concurrent migration-batch telemetry (and its own count assertion was
polluted in return). Assertions now filter by a per-run call_id prefix
and teardown deletes only its own rows.
iomgaa