feat: Prosa ist kein Identifier - Link-Taxonomie als Enum, generierte Regionen mit Markern (4.0.0)

Files changed:
- .gitea/workflows/ci.yml
- AGENTS.md
- CHANGES.md
- VERSION
- instructions/CONTRACT.md
- instructions/link-taxonomy.md
- instructions/migrations/4.0.0-link-taxonomy.md
- instructions/setup-instance.md
- kb/CONTRACT.md
- kb/CONVENTIONS.md
- kb/CONVENTIONS.md.template
- kb/comparisons/COLLECTION.md
- kb/concepts/COLLECTION.md
- kb/entities/COLLECTION.md
- kb/sources/COLLECTION.md
- tools/CONTRACT.md
- tools/README.md
- tools/chemenu/blocks.py
- tools/chemenu/cli.py
- tools/chemenu/commands/cite_cmd.py
- tools/chemenu/commands/dist_cmd.py
- tools/chemenu/commands/docs_verify.py
- tools/chemenu/commands/doctor.py
- tools/chemenu/commands/links_cmd.py
- tools/chemenu/commands/migrate_cmd.py
- tools/chemenu/commands/new_page.py
- tools/chemenu/commands/page_ops.py
- tools/chemenu/commands/run_budget.py
- tools/chemenu/commands/xref.py
- tools/chemenu/conventions.py
- tools/chemenu/corpus_diff.py
- tools/chemenu/frontmatter_io.py
- tools/chemenu/kb_collections.py
- tools/chemenu/kb_state.py
- tools/chemenu/links.py
- tools/chemenu/lint_core.py
- tools/chemenu/provenance.py
- tools/chemenu/sections.py
- tools/chemenu/tests/conftest.py
- tools/chemenu/tests/test_blocks.py
- tools/chemenu/tests/test_cite_cmd.py
- tools/chemenu/tests/test_conventions.py
- tools/chemenu/tests/test_dist_cmd.py
- tools/chemenu/tests/test_doctor.py
- tools/chemenu/tests/test_migrate_cmd.py
- tools/chemenu/tests/test_new_page.py
- tools/chemenu/tests/test_pipeline_l0.py
- tools/chemenu/tests/test_types_cmd.py
- tools/chemenu/tests/test_xref.py
- types/concept.schema.yaml
- types/entity.md
- types/entity.schema.yaml
- types/instruction.schema.yaml
- types/type-spec.md
- work/link-taxonomy-migration/README.md
- work/link-taxonomy-migration/plan.md

instructions/CONTRACT.md

@@ -65,11 +65,31 @@ catalogue of authoring profiles an instance may adopt into its own `kb/CONVENTIO
 
 ## `instructions/migrations/`
 
-A content migration is a Manual instruction with two extra frontmatter fields
+A content migration is a Manual instruction with three extra frontmatter fields
 (`types/instruction.schema.yaml`): `migrates_to:`, the stack version whose content shape it
-produces, and `migration_kind:` (`mechanical` | `assisted`). It lives at
+produces; `migration_kind:` (`mechanical` | `assisted`); and `obligation:`
+(`required` | `offered`, default `required`). It lives at
 `instructions/migrations/<version>-<slug>.md`.
 
+`migration_kind:` and `obligation:` are **two axes, not one**. The first says how the work is
+carried out, the second whether it has to happen at all:
+
+| `obligation:` | Means | `migrate status` |
+|---|---|---|
+| `required` | The content must reach the new shape or it no longer fits the machinery | Counted as outstanding; `migrate done` advances `kb_version` through it, in chain order |
+| `offered` | A file the instance owns still works as it is, and the stack proposes a better default | Listed separately, never blocks, no ordering rule. `migrate done` records it in the applied ledger and leaves `kb_version` where it is |
+
+Keeping them apart is what stops `migrate status` crying wolf: an instance nagged about an
+improvement it declined stops reading the nag that means its content no longer fits its
+machinery. And because taking an offer deliberately does not move the version, the **applied
+ledger** - not `kb_version` - is what makes an offer stop being offered; without that record
+there is no way to tell a taken offer from an ignored one.
+
+An `offered` migration is what makes an instance-owned file upgradeable at all. `dist export`
+records a sha256 per shipped file in `.wikitool-release.json`, so `migrate status` can say which
+of those files the instance edited and which it merely received - the first have to be
+reconciled by a person, the second can simply be copied over.
+
 The tier fits exactly: a migration must never be picked up implicitly - it rewrites the corpus -
 and it is referenced by nothing, because `tools/wikitool migrate status` finds it by reading the
 directory and comparing `migrates_to:` against this instance's `kb_version`. That is also why