Database schema is declared across 16 modules with no migration mechanism

16 modules each ran CREATE TABLE IF NOT EXISTS on connect with no version tracking, so an ALTER TABLE / column rename had no safe path. FIX 7e648a6: db.migrate(conn, name, steps) — an ordered, append-only list of DDL scripts recorded per database file in a dsc_schema_version table; step i moves the schema from version i to i+1, each step and its version row commit in the SAME transaction (a crash mid-migration leaves either the old or the new version, never a half-applied step), a pre-mechanism database adopts version 1 on first contact, and it is coordinated with schema_once so two threads on first use do not both migrate. db.schema_version(conn, name) reads the recorded version. Tests: test_db_migrate.py (order, resume, failed-step-rolls-back, pre-mechanism adoption). SCOPE: the mechanism now EXISTS and is live in the container; the 16 existing modules still call ensure_schema/schema_once and opt in incrementally by replacing that with migrate(conn, name, [SCHEMA, …alters]) when they next need a column change. So this is the mechanism, not a bulk conversion. Verify: import dsc_brain.db; db.migrate / db.schema_version present (confirmed in the running 8.1.0 image).