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

planning/stages/S00.md

@@ -23,7 +23,7 @@
 - [S00-016](../tasks/S00-016.md): Restore reviewer model availability after provider capacity failure — ci-cd; done.
 - [S00-017](../tasks/S00-017.md): Establish fail-closed SCRAM server-final validation — protocol; done.
 - [S00-018](../tasks/S00-018.md): Validate bounded standalone XML ingress for the XMPP candidate — protocol; done.
-- [S00-019](../tasks/S00-019.md): Validate browser-compatible SCRAM-SHA-512 through a public mechanism API — crypto; todo.
+- [S00-019](../tasks/S00-019.md): Validate browser-compatible SCRAM-SHA-512 through a public mechanism API — crypto; review.
 - [S00-010](../tasks/S00-010.md): Gate: Профиль и проверка стека — qa; todo.
 
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