Evaluate Stanza with verified SCRAM and bounded WSS ingress

Changes: Propose the pinned XMPP library decision and add an isolated browser-built selection spike combining reviewed public SASL, SHA-512 and parser seams. Exercise TLS/xmpp handshake, strongest compatible non-PLUS authentication, rejected unsafe paths and extension mappings; document duplicate-body export projection and remaining limits. Preserve dependency notices, evidence and QA handoff.
Validation: Clean-cache pinned npm ci succeeded; npm test passed 112 checks; check-dependencies.py verified 51 locked entries, 26 installed packages and 340 unchanged vendor files; make check passed 72 tooling tests. No actual browser runtime, independent full XMPP server/client or production encryption/release readiness claim.
