CND 0.5.0 core: rich text, block containers, traversal, validation, hashing

[Maxanox]

Moves the SDK core to format 0.5.0, following proposal 0013. This is the first of the three plans that land on the format-0-5-0 integration branch.

What changes

• Rich text (cnd.core.text): RichText, Mark and Numbering. The four edge families now live on RichText instead of the node base.
• Node model:
  • prose is RichText;
  • every container holds nodes in children: list items, term definitions, cells, quotes, admonitions, footnotes;
  • new admonition and layout nodes;
  • ListItem.checked, figure.description, code.title and numbering;
  • table.kind (data / content / null);
  • doc.status, doc.version and doc.extra.
  • tight, content_kind, table.raw and the block flags are removed.
• Traversal enters every container. Each visited node carries slot, slot_index and a full path. Cnd.iter_all() also walks footnote content.
• Validation adds:
  • the mark rules (bounds, canonical order, same-kind merge, atomic code/math);
  • text span bounds;
  • the doc.extra key rule;
  • global id uniqueness.
    Every check now reaches footnote content and the formatted bibliography entries.
• Hashing:
  • default-valued fields are dropped, and the schema now states every default;
  • nested nodes are excluded from a node's hash;
  • the document hash pairs every node with its path.
  • Vectors are regenerated, and a twin fixture with every default written out proves that omission does not change a hash.
• Fixtures are migrated to 0.5, and elements.cnd covers every new element.
• Spec and ADRs: the spec is rewritten for 0.5.0. New ADRs 0025 (edges belong to rich text), 0026 (open vocabularies), 0027 (no compatibility guarantee before 1.0) and 0028 (hashing; supersedes 0016).

Not in this pull request

Ten test modules are parked in tests/conftest.py (collect_ignore): builder, CLI, converters, declaration, full coverage, Markdown structure, display visitor, reconciliation, render and visitor. The next two plans port renderers and converters, then the declaration, builder, reconciliation, CLI and visitors. format-0-5-0 merges into main only once that list is empty.

The suite is green: 199 passed. Every task was reviewed, and the whole branch had a final review, with its findings fixed.

Part of CND-17

🤖 Generated with Claude Code

https://claude.ai/code/session_01XxXUiDn2QyzNTYnZpeVFVS