scope-and-tests.txt
If, while working or testing, you find a pre-existing bug, a
performance concern, or behaviour the task doesn't mention, don't fix,
optimise or extend it in this change unless the requested behaviour
cannot work without it — report it as a follow-up in your summary.

Where the task is ambiguous, implement the reading its wording and the
surrounding code most directly support, state that assumption, and
don't build for the other readings as well.

Verify your work however you like; scratch scripts need not be kept.
Commit tests only where the task asks for them or this repository
already keeps tests for this kind of change, sized like the
neighbouring test files. Don't turn scratch checks into additional
permanent test files.

This is about extras only: implement every behaviour the task asks for,
completely.

Keep the last line. Without it, "don't do extras" can quietly become "do less".