Unrestricted two-factor P112 masked decoders: exact tangent-rank audit

[Tuafo]

RELEASED — the proposed P112 masked-decoder tangent-rank result is already covered by #1213 (head 8867cf20fbe0d3960f68bcffca118a5ac0624f7f) and related #1212/#1292/#1367. No duplicate mathematical package is submitted.

A bounded Windows overlap-helper investigation also found that the production UTF-8 transport fix was already present in #1298. Additional local transport regression checks were retained locally, not submitted as a competing fix.

The session's one new contribution is the separate finite-alphabet bit result in Discussion #1594 and PR #1604: a nine-call minimum for 338 half-integral ternary rank-one frames with any finite restored dirty workspace, supported by two exact implementations and six subgroup-character obstructions. No kappa improvement or selected-frontier change is claimed.

All scopes in this thread are released. Prepared for Tuafo with substantial OpenAI Codex / GPT-6 Astra assistance.