nx_esign_lib.nx

nx_esign_lib.nx -- E-SIGNATURE LEGAL VALIDITY: the ESIGN/UETA four-element test + the eIDAS tier ladder (SES/AES/QES). The gap this closes: a tamper-evident hash chain (nx_sign_envelope) proves a document was NOT ALTERED. It does not answer the only two questions a court asks -- was this signature legally executed, and what legal effect does it carry. DocuSign/Adobe-class products answer both; a bare hash chain answers neither. US (ESIGN 15 USC 7001 + UETA s2(8)/s7): enforceable ONLY on all FOUR of -- 1 INTENT the signer performed an affirmative act intending to sign 2 CONSENT the parties agreed to transact electronically 3 ASSOCIATION the signature is logically/cryptographically bound to THAT record 4 RETENTION the record is tamper-evident, accurately reproducible, and accessible CONSUMER OVERLAY (ESIGN 101(c)) -- a consumer signer additionally requires paper-copy right, withdrawal right, hardware/software disclosure, and a DEMONSTRATED ability to access the record. A consumer transaction missing these is unenforceable even with all four base elements present. EU (eIDAS Art 3/25/26): SES < AES < QES. THE DISTINCTION MOST IMPLEMENTATIONS BLUR: Art 25(1) says no electronic signature may be denied legal effect merely for being electronic -- that is ADMISSIBILITY, and it reaches every tier. Art 25(2) grants EQUIVALENCE TO A HANDWRITTEN SIGNATURE to QES *alone*. Conflating them is the error that loses cases, so they are SEPARATE predicates that never collapse. STRUCTURE (two layers, deliberately): a PURE DECISION CORE holding the statutory rules as total functions over resolved flags, and REGISTRY ADAPTERS that fetch facts and delegate to it. Every rule exists exactly once, so the stored-fact path can never disagree with the rule. See the core's own note for why this split is load-bearing rather than cosmetic. FAIL-CLOSED BY CONSTRUCTION: only the exact string "yes" asserts a stored element, and only the integer 1 asserts a resolved one. Absent, empty, "true", "1", "YES" all leave it UNSATISFIED. An element nobody recorded is an element nobody performed; a signature is never valid by omission. SCALE ENVELOPE (declared, measured): the pure core is O(1) and allocation-free. Each adapter costs one reg_get per element (~70us). reg_put costs ~678ms and is the binding cost of WRITING facts, never of evaluating them -- see debt 1785519597. license_tier: ORIGINAL LIB.