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/glossary.md

@@ -87,6 +87,14 @@ Deferred edges for later units, discovered while processing systems:
   entity-to-concept for authorship. Resolved as `see-also` in every such case on Karpathy's,
   Gupta's and Bush's own pages, checked against every register first - not a stretch, a genuine
   gap. Worth proposing a label (`originates`/`authored-by`?) if this recurs in u3/u4.
+- **`kb/sources/` pages carry no `related:` field either, same as comparisons.**
+  `types/source.md` declares only `page_ref_fields: [entities, concepts]` - `xref add` refuses
+  there with the identical "type does not declare a related: field" error. Unlike comparisons,
+  though, there is nothing left to migrate by hand: every one of the 27 source pages already had
+  `entities:`/`concepts:` correctly populated via `xref link-source` at ingest time, and their
+  prose "Verwandte Entities"/"Verwandte Concepts" sections already just mirror those fields -
+  there was never a labelled-vs-unlabelled distinction to fix here. `migrate verify --from
+  177c7e9 --path kb/sources` returns 0 findings against baseline. u4 closes with zero page edits.
 - **comparisons pages carry no `related:` field at all.** `types/comparison.md` declares only
   `entities` (`page_ref_fields: [entities]`) - unlabelled by the schema, like `sources:`. `xref
   add`/`xref remove` refuse on this type ("type does not declare a related: field"). The