Approve pinned Linux XMPP toolchain restoration

Changes: Accept S00-020 with independent QA evidence and handoff; refresh scoped runtime/cache result paths after fresh retrieval and installation.
Validation: verify.py passed official HTTPS checksum, Node 24.21.0/npm 11.19.0, isolated strict npm ci and Stanza import. Independent archive/input/eight-version/strict-setting assertions, tasks.py validate and diff/scope checks passed. Browser/WSS and product readiness remain untested.
