ADR 0012: Classifier string patterns are versioned, fixture-backed, and counted

Status

Accepted (2026-08-13).

Context

A billing wall misread as RPM is the highest-cost classification bug.

Decision

Spend markers live in _SPEND_MARKERS. Golden fixtures under tests/fixtures/errors/ lock the ladder. classify_explained names the rung. Ambiguity defaults to a bounded unknown window.

Consequences

Recorded in architecture §19. Changing this ADR requires a new numbered record, not a silent edit of the classifier or ports.