S00-020: Verify pinned Linux XMPP toolchain restoration

Changes: Refresh the environment-access result and document S00-020 restoration, accepted prerequisites and independent QA handoff; preserve probe code and parent dependency graph.
Validation: verify.py passed official HTTPS vendor checksum, Node 24.21.0/npm 11.19.0, fresh-cache strict npm ci and Stanza import. Separate artifact/input/version/strict-setting assertions and tasks.py validate passed. No browser/WSS or product readiness check performed.

Task: S00-020
Agent: auto-ci-cd-2a0186c54ce9
Role: ci-cd
Action: claim
Status: review

Task title: Restore access to the pinned Linux XMPP experiment toolchain

planning/stages/S00.md

@@ -24,7 +24,7 @@
 - [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; done.
-- [S00-020](../tasks/S00-020.md): Restore access to the pinned Linux XMPP experiment toolchain — ci-cd; todo.
+- [S00-020](../tasks/S00-020.md): Restore access to the pinned Linux XMPP experiment toolchain — ci-cd; review.
 - [S00-021](../tasks/S00-021.md): Устранить прерывание: Проверить browser OMEMO backend — crypto; done.
 - [S00-022](../tasks/S00-022.md): Confirm or source a verified browser/WASM-capable OMEMO2 backend for the Web client endpoint — crypto; blocked.
 - [S00-023](../tasks/S00-023.md): Устранить прерывание: Выбрать IndexedDB wrapper и migration policy — storage; blocked.