The reconstruction verifier re-walked the ledger bounded by `fit_as_of` and
reported DIFFERS for a completely healthy artifact. The artifact had not moved —
its knot, curve and source digests on disk were byte-identical and the runtime
was serving exactly them. The TRAINING SOURCE had moved.
Measured: the artifact was built at 05:xx UTC with 6,069 rows through
2026-09-01. By 20:00 UTC a re-walk at the same fit_as_of returned 6,237, because
2026-09-02's 168 rows settled in between. Settlement backfills dates that are
already before the cutoff, so `fit_as_of` bounds eligibility but does not pin
membership.
`training_cutoff` — the newest observation actually admitted — does pin it,
because those dates are fully settled. Re-walked under that bound the
reconstruction is EXACT: fit_n, training_cutoff, source_digest, knot_count,
knot_digest, served_curve_digest all equal and the curve identical.
This is why the two fields were kept separate and why source_digest exists. The
digest caught a moving source and refused to call it a match, which is the
behaviour that made the diagnosis possible.
No artifact change. No model change. The verifier now states the bound it used.
Suite 405/405.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CQJeAG8vcDoL5zkiaJyVb8
builtbykev
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