The vault's `independent_roots` field and the medieval système de preuve légale are both graduated bookkeeping with narrow categorical chokepoints — not the flat two-witness bar either is usually described as

legal-historyvault-epistemologyindependent-rootspreuve-legalesource-disciplinecross-domain-bridgemeta-analysiscorroborationbridge-check

observation-vault-source-tiers-revive-preuve-legale-run-in-reverse (drafted 2026-07-12) reads the vault's source-tier apparatus as reviving Roman-canon proof law, citing the vault's refusal of a same-mirror re-read as corroboration as the modern echo of a two-witness requirement. The vault's own independent_roots field — the mechanism that bookkeeping most naturally names, formalized eleven weeks later (Stochastic-design proposal §3b, applied 2026-09-28) — turns out, on direct examination, to be narrower and softer than that framing suggests: per claim-independent-roots-is-bookkeeping-not-a-categorical-bar, it hard-gates only at draft promotion and at the single-source concentration cap, and otherwise leaves a independent_roots: 1 claim standing, flagged, at status: seedling, indefinitely.

The historical side of the comparison was never a flat bar either. Roman-canon law rated a single eyewitness or private document as probatio semi-plena (half-proof), with two half-proofs capable of summing to probatio plena (claim-roman-canon-law-rated-one-witness-equal-to-a-private-document) — except, per a still-[unverified -- needs primary] claim, in grave criminal, matrimonial, and serious civil cases, which demanded proof "clearer than the noonday sun" (claim-two-half-proofs-combined-to-full-proof-except-in-grave-criminal-cases).

Put together, the resemblance between the vault's mechanism and the historical system is real but is a correction, not a confirmation: both are graduated accounting systems that reserve categorical refusal for a small number of named, high-stakes chokepoints, rather than the blanket unus testis, nullus testis bar the "two witnesses" framing evokes on a plain reading. The original observation's "run in reverse" headline survives directionally; its specific "explicitly refuses... as corroboration" language is the part this note narrows.

Further leads

• question-verify-half-proof-combination-rule-criminal-exception-primary — the open verification this note's weakest leg still rests on.
• Whether root_shared has a combination rule of its own, analogous to the criminal-case exception, is raised but not answered here.