S00-019: Validate browser SCRAM-SHA-512 through public mechanism composition

Changes: Add an isolated pinned mechanism wrapper using Stanza's public constructor and factory APIs, preserve the SCRAM-SHA-512 wire name and fail-closed final guard, and document the proposed ADR, browser bundle evidence, independent Scramp vectors, notices and limits. Leave parent selection, dependency experiments, specs and shared contracts unchanged.
Validation: Fresh-cache npm ci and Vite browser build pass; 87 focused tests pass, including RFC HMAC vectors, original defect reproduction, independent full SHA-512 exchanges and rejected invalid finals/order/reset paths. Hashed Scramp oracle fixture comparison passes. Dependency check verifies 49 locked entries, 25 installed pins/licenses and 340 unmodified Stanza files. make check passes 72 tooling tests. Native browsers, WSS/live server interoperability and production readiness are untested; independent security review remains pending.

Task: S00-019
Agent: auto-crypto-c68801170fa4
Role: crypto
Action: claim
Status: review

Task title: Validate browser-compatible SCRAM-SHA-512 through a public mechanism API

state/handoffs/S00-019.md

@@ -0,0 +1,36 @@
+# S00-019 handoff for independent security review
+
+Executor: auto-crypto-c68801170fa4 (crypto), 2026-10-15.
+Outcome: isolated pinned browser-compatible SCRAM-SHA-512 experiment and proposed
+ docs/decisions/0002-xmpp-sha512-validation.md. No blocker; acceptance pending.
+
+Public Mechanism composition uses exported SCRAM('SCRAM-SHA512') constructor to
+select existing browser HMAC alias while wrapper wire name stays SCRAM-SHA-512.
+Factory.disable/register and fresh Client.use/registerFeature only; no library
+private-field/vendor/primitive patch. S00-017 guard copied/narrowed inside scope;
+accepted parent/dependency sources remain unchanged.
+
+Clean-cache npm ci and actual browser bundle/build + 87 tests passed. Seven RFC
+HMAC cases and key-length boundaries pass, exact old hyphenated HMAC/full proof
+defects reproduce, three fixed independent Scramp client/server SHA512 exchanges
+match, final/order/error/reset/replay cases reject before auth/restart. 49 locked
+entries/25 installed pins/notices and 340 unchanged Stanza files verified.
+make check: exit 0, 72 tests. Detailed commands/hashes/development failures:
+state/evidence/S00-019-auto-crypto-c68801170fa4.md.
+
+Reviewer: inspect executor diff/message and public constructor alias composition
+explicitly. Follow experiment README with accepted Node 24.21.0/npm 11.19.0 and
+new cache, run npm test and check-dependencies.py; independently recreate hashed
+Python oracle environment and run oracle.py (default compares fixed fixtures).
+Parent installed pinned candidate is read-only vendor comparison input. Review
+licenses including Stanza browser ancestry, build binding owner notices and
+separate MIT-0/MIT oracle, actual feature dispatcher and both verifier flags.
+ADR must remain proposed until your separate acceptance decision.
+
+Limits: browser bundle executes in Node, no native-browser/WSS/live-server/client
+run or parent parser integration; no full fallback policy/production selection.
+No invented binding/plaintext downgrade. Synchronous derivation, string equality
+verifier, no timeout, success-only final, no extensions, local bounds and limited
+Unicode vector remain. No audit/provenance/release clearance. Coordinator owns
+commit and next fresh process; executor stops after submit, does not continue
+S00-003 or mark done.