tddlisted

# Failing test first [`CONTRIBUTING.md`](../../CONTRIBUTING.md) asks contributors to write the test first _"when you can"_. For an agent that is not a preference, it is the rule — because the thing an agent does wrong that a human does not is quietly adjust the expectation until the bar clears. ## The rule 1. Write the test first. 2. **Watch it fail**, and check it fails for the reason you expect. A test that passes before the fix is testing nothing. 3. Make it pass. 4. **Never weaken an expectation to make it pass.** When a test resists, the test is usually right — several bugs here were found by agents that refused to relax one. Loosening an assertion, widening a tolerance, deleting a case, or adding a conditional skip in order to go green are all the same move, and all of them are the failure this rule exists to stop. ## Prove a decision that carries weight When a choice is load-bearing, break it deliberately and confirm the **specific** test that should fail does fail. Two designs that looked fine were caught this way. Undo the break immediately. ## House idioms Copy these rather than inventing a style — verified against the suite: - **Hand-written fakes, not `vi.mock`.** The named ones are `fakeFs.ts`, `fakeHookFs.ts` and `memorySqlite.ts`; `CONTRIBUTING.md` gives their paths. `vi.mock` appears in only 2 test files (5 occurrences) in the whole suite, so reaching for it means you are probably going against the grain. - **Injected clocks.** Where a mod