Duplicated-fact drift is the fourth error class and the only one with no
executable rule. No positive control catches it (both copies are
internally consistent) and re-derivation does not either (the copy
reproduces whatever it was copied from). It is caught only by reading a
copy against its source, which nothing in the loop required.
facts.toml holds 15 facts and is GENERATED by `make facts-gen` from
cb-cost, dep-weight and rule-coverage. The trap this task named — a
hand-maintained registry that becomes another drifting copy — is closed
by facts-check re-running the instruments and failing when the committed
registry disagrees with them. A stale registry cannot certify stale
artifacts.
An artifact quoting a fact tags it: **$93.15** <!-- fact --> with the key.
17 occurrences across 5 artifacts are now checked.
Falsified before being believed: changing CostAccounting.md line 158 from
$93.15 to $92.87 — the exact historical drift — produced exit 1 naming
the file, the line and the expected value. Tested against the class it
exists to catch, on a real artifact, not only in its self-test.
It then caught a live tag inside its own documentation example in
InnerLoop.md within the hour. Third time a gate has failed on its own
pass's work.
What it does not close is stated rather than implied: 22 untagged literal
copies remain and are reported, not failed. Tagging is opt-in, a number
can legitimately recur, and a gate that fires on coincidence gets routed
around. Naming the uncovered surface beats claiming the class is closed.
InnerLoop single-source-of-fact moves from prose to executable — v1.3.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
tegwick
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