- Replace the static initialDatabases list (13 named DBs reset with TRUNCATE) with three golden templates: golden_en57, golden_res, and golden_en57_seeded. The seeded golden bakes its 1M-row seed in at provisioning time. - Add En57::EphemeralDatabase.with(template:), which clones a golden via CREATE DATABASE ... TEMPLATE (PostgreSQL's fastest copy — file-level, not row-by-row), yields a database_url, and drops it WITH (FORCE) when the block ends. No TRUNCATE. - IntegrationTest now clones golden_en57 per test and drops it on teardown, isolating every test; pools connect lazily. Benchmarks clone per scenario instead of resetting. - The seeded benchmark clones the 1M-row golden (~1s) instead of re-INSERTing the seed on every run (~16s). - Ignore EphemeralDatabase#execute in mutant: the receiver->self mutation runs Kernel#exec on multi-word SQL and replaces the worker, so it cannot be killed. - Adopting this needs a one-time Postgres data-dir reset so devenv provisions the goldens (devenv up and devenv test use separate state dirs); the old named databases are obsolete.