Metadata model rules

Metadata changes must preserve these invariants:

  • vocabulary and property identifiers are open strings, not closed enums;

  • unknown terms remain readable without a registry;

  • repeated assertions are distinct from one list value;

  • list order and structured-field order are preserved;

  • persistence never uses floating point or unconstrained JSON as the canonical form;

  • every constructor enforces the public size and nesting limits;

  • malformed stored values produce ErrorKind::Storage, never a panic;

  • metadata remains on its explicit target and is never copied implicitly;

  • the private encoding version is checked before any value is decoded.

The deterministic encoding lives in the SQLite crate because it is a storage choice, not a core domain contract. Do not expose encoded blobs through Rust, C, C++, CLI, or Python APIs. Public adapters inspect values by type and recurse through lists and structured fields.

Adding a vocabulary mapping does not make PostProject normative for that standard. Link to the authoritative vocabulary, document mapping strength, and preserve source values that the helper does not understand. Do not copy a full third-party vocabulary into the repository without reviewing its license and maintenance implications.

Registry additions must remain small and evidence-based. Use the exact published vocabulary and property spellings, cite the authoritative source, and add tests for lookup, advisory validation, and unknown-term behavior. Descriptions should be concise paraphrases unless the source license and need justify copying text. Mapping aliases identify a profile-specific correspondence; they do not become additional persisted identities or imply lossless conformance. Registry validation must be deterministic and local: no network access, dynamic code, normalization, or mutation of caller values.

PostProject-owned vocabulary identifiers belong below https://postproject.org/ns/. Application-specific terms belong below a namespace controlled by that application, not below the PostProject namespace.

Schema, encoding, limit, or public-type changes require an ADR review, malformed input tests, round-trip tests, migration coverage, and corresponding updates to every public adapter that already exposes metadata.