update: u4 (kb/sources) als abgeschlossen dokumentiert - keine Aenderungen noetig

Files changed:
- work/link-taxonomy-migration/README.md
- work/link-taxonomy-migration/glossary.md

work/link-taxonomy-migration/README.md

@@ -70,7 +70,11 @@ Every unit in `plan.md` is published, and:
       alongside a bare wikilink during prose cleanup, caught by `migrate verify`'s `cite-refs`
       diff and restored. Published as commit `a35c94e`. See `glossary.md` for the
       add-is-safe/remove-is-risky mechanism note this unit established.
-- [ ] u4 `kb/sources/`
+- [x] u4 `kb/sources/` - zero page edits needed. `types/source.md` declares no `related:` field
+      (only `entities:`/`concepts:`, same structural gap as comparisons), and all 27 source pages
+      already had those fields correctly populated via `xref link-source` at ingest time - there
+      was never an unlabelled edge here to fix. `migrate verify --from 177c7e9 --path kb/sources`:
+      0 findings. No commit, no session id spent beyond the check itself. See `glossary.md`.
 - [ ] u5 close-out - `migrate done`, version bump, `CHANGES.md`, workshop close
 
 ## Measured after u0