First slice of the per-stage batch-transaction refactor (ADR-0012). A
UnitOfWork is the single transaction a stage runs its batch in: a context
manager exposing the DB repos bound to one session, committing once on
`commit()` and rolling back on exception or exit-without-commit
(all-or-nothing per batch, fail noisily).
- `UnitOfWork` (port): `property` / `epc` / `solar` / `baseline` repos +
`commit()` / `rollback()`; `__exit__` rolls back uncommitted work.
- `PostgresUnitOfWork(session_factory)`: opens a Session from an injected
factory (a module-scoped engine + sessionmaker in prod, so the pool is
reused across warm invocations), binds the Postgres repos to it, closes
on exit.
Not yet wired into any orchestrator — that lands in the Baseline /
Ingestion refactor slices. 3 tests against ephemeral PG (commit durable
across units; exception rolls back; no-commit persists nothing). pyright
strict clean; AAA.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>