The integration suite registers around thirty-five customers and asserts nothing about any of their hashes, yet paid bcrypt cost 12 for every one. bcryptjs is a pure-JS implementation, so it pays that cost several times over compared with a native build, and hashing was most of the suite's wall clock. On a contended runner it pushed adminInventory.integration.test.ts past its twenty-second timeout, which then surfaced as a foreign key violation somewhere else entirely — the test timed out, jest moved on, beforeEach truncated, and the still-in-flight registration wrote a token for a customer that had just been deleted.
Measured rather than asserted, warm run against warm run with only the constant changed: 34.5s at cost 12, 9.8s at cost 4. Three and a half times faster, about twenty-five seconds off every integration run, with all 263 tests passing either way.
The first attempt at that measurement was wrong and worth recording. Comparing a cold run at cost 4 against a warm run at cost 12 made the change look like a 36% regression-shaped improvement of the wrong size; the difference was ts-jest and Postgres warming up, not the cost factor. Both numbers above are second runs, and the cost-12 figure was taken twice — 34.3s and 34.5s — before being believed.
Deliberately not configurable. An environment variable here would be a way to weaken password hashing in production by misconfiguration, and nothing needs to tune it. The only route to the cheap cost is NODE_ENV=test, which a deployed container would announce anyway by refusing to serve the built frontend, since app.ts gates static serving on the same value. A setting that quietly degrades a security property should be unreachable rather than warned about, which is the reasoning that already made DEMO_MODE strict.
`hashRoundsFor` is pure and separately tested because the failure it guards against is silent: only the exact string 'test' earns the cheap cost, and an unset NODE_ENV gets the strong one, so the dangerous direction has to be asked for explicitly. Both constants are pinned by assertions too — without that the branch tests pass while the numbers drift to something useless.
Closes#242
