Phase B closed:
- slice 4c: text payloads in variant arena entries (#48)
- label_tree worked example + nested VariantConstruct fix (#50)

Phase C — structural recursion proofs (3 slices):
- slice 1: structural recursion proof for concept_group types (#49)
- slice 2: decreasing numeric field proof (#51)
- slice 3: increasing numeric field proof (#55)

The compiler now PROVES termination structurally for recursive rules
over concept_group types and bounded numeric fields. The mandatory
breadcrumb from Phase A ('not proven structurally') is being replaced
by verified proofs.

New features:
- Mutable service state: state:/after: blocks (#47)
- Text input fields in recursive callables (#52)
- scan_word: first recursive text scanner (#53)
- Let bindings in recursive callables (#54)

12 commits post-v0.5.0. Tests 348+.