What a database driver with no transactions actually costs

The tests were green. All 1,257 of them.

getDb() returned a neon-http client and cast it to NodePgDatabase. That cast is the whole bug. neon-http has no transactions, but the type says it does, so db.transaction() compiles cleanly and throws only when it runs, under a driver the tests never used.

What that buys you is a suite proving the code typechecks and proving nothing about whether it works. The failure surfaced in production, on every call, as a 500.

Two things came out of it. Concurrency that leaned on a transaction is now a unique index plus ON CONFLICT, which the database enforces whether or not the driver can hold a transaction open. And the test database driver matches the deployed one, because a test running on different infrastructure from production is testing different software.

The general form is worth more than the specific fix. A cast is a claim you make to the compiler, and the compiler believes you. If the claim is wrong, every test downstream of it is measuring the wrong thing, and the greener the suite the longer it takes anyone to notice.