docs: close navigation and mission archive gaps

docs/USER-GUIDE/README.md

@@ -7,7 +7,7 @@ This book is the canonical home for end-user workflows, user-visible behavior, p
 ## Start here
 
 - [Documentation atlas](../README.md) — placement rules and source-of-truth boundaries.
-- [Documentation sitemap](../SITEMAP.md) — existing navigation is transitional and still contains legacy paths.
+- [Documentation sitemap](../SITEMAP.md) — resolvable current navigation and authority-gated migration summary.
 - [Quickstart](getting-started/quickstart.md) — install Mosaic, complete setup, and launch a session.
 - [Web dashboard](product/web-dashboard.md) — current routes, navigation, chat persistence, projects/tasks views, settings, and admin behavior.
 - [Discord conversations](workflows/discord-conversations.md) — current authorized parent-channel, thread, attachment, and control workflow.
@@ -34,8 +34,8 @@ Every promoted page must be added to this index and to [`SITEMAP.md`](../SITEMAP
 
 These are source candidates, not current user guidance:
 
-- [`_old_structure/guides/user-guide.md`](../_old_structure/guides/user-guide.md) — historical source; verify every claim before promotion.
-  The former root `QUICKSTART.md` was an empty placeholder and has been replaced by the current page above.
+- `_old_structure/guides/user-guide.md` — quarantined historical source; verify every claim before promotion. See the [documentation catalog](../reports/documentation/2026-08-10-docs-catalog-audit.md) for its disposition.
+- The former root `QUICKSTART.md` was an empty placeholder and has been replaced by the current page above.
 
 Do not link to the quarantine as a current user path. Create a new page only after classifying its audience, status, and evidence in the migration report.