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/tasks.json

@@ -1,6 +1,6 @@
 {
   "schema_version": 1,
-  "revision": 48,
+  "revision": 50,
   "tasks": {
     "S00-001": {
       "status": "done",
@@ -1249,10 +1249,14 @@
       "completed_at": "2026-10-14T19:35:55+00:00"
     },
     "S00-019": {
-      "status": "todo",
-      "owner": null,
+      "status": "review",
+      "owner": "auto-crypto-c68801170fa4",
       "external_wait": false,
-      "reason": null
+      "reason": null,
+      "started_at": "2026-10-14T19:38:43+00:00",
+      "updated_at": "2026-10-14T19:48:39+00:00",
+      "evidence": "state/evidence/S00-019-auto-crypto-c68801170fa4.md",
+      "handoff": "state/handoffs/S00-019.md"
     }
   },
   "events": [
@@ -1878,6 +1882,29 @@
       "from": "in_progress",
       "to": "blocked",
       "reason": "Stanza 12.22.1 browser HMAC sha-512 fails RFC 4231 Test Case 1: wrong 64-byte block selection. SCRAM-SHA-512 derives that hyphenated algorithm; private algorithm mutation/vendor patches are unsupported. Parent cannot attest browser strongest-mechanism compatibility from Node-only success."
+    },
+    {
+      "revision": 49,
+      "at": "2026-10-14T19:38:43+00:00",
+      "action": "claim",
+      "task": "S00-019",
+      "agent": "auto-crypto-c68801170fa4",
+      "role": "crypto",
+      "from": "todo",
+      "to": "in_progress",
+      "reason": null
+    },
+    {
+      "revision": 50,
+      "at": "2026-10-14T19:48:39+00:00",
+      "action": "submit",
+      "task": "S00-019",
+      "agent": "auto-crypto-c68801170fa4",
+      "role": null,
+      "from": "in_progress",
+      "to": "review",
+      "reason": null,
+      "evidence": "state/evidence/S00-019-auto-crypto-c68801170fa4.md"
     }
   ],
   "retired_agents": [