A narrow instrument does not answer a wide question

Reading CI Signals collects rules for what a check's colour actually means. Most of them turn out to be instances of a single shape that the page had never named, and naming it is worth a section because the instances keep arriving in new costumes.

The shape: a narrow instrument returns a correct answer, and the reader generalises it into a claim the instrument was never measuring. There is no bug to find and no error to notice — the measurement is right and the reading is wrong, which is precisely why care does not catch this class and a control does.

Five cases were measured in one session, while triaging two long-running issues. Four are CI instruments; the fifth deliberately is not, because the shape is about how an answer is read:

• pendingWork=0 on one stale-callback record, read as "the pool is idle" — which killed a live hypothesis. Maximum pendingWork in the same log is 606, and 2,501 across the run set.
• A count filtered to one gate stage, published as an occurrence count: 8 where the real figure was 15, because seven siblings failed at a different checkpoint on the same mechanism.
• gh api … 2>/dev/null over eight repositories reporting every one clean, when every call was in fact being refused and the discarded stderr was the only place that said so.
• A quota endpoint reporting 5000/5000 remaining while every call was refused — an honest meter, answering about the primary limit when the refusals were the secondary one.
• A GitHub App's declared permissions read as what a token can do. The App declares issues and workflows; the installation that mints the token carries neither.

The section gives the test to apply before a number becomes a verdict — name the question the instrument actually answers, then say why that is the same as the question you asked — plus the specific tell for each family: state the maximum and the count rather than the sample, state the filter beside the number, check the exit code rather than suppressing it, and read the refusal rather than the meter.