IcyDB Schema

Schema AST, validation, and builder utilities used by IcyDB macros and planning layers.

End-user canister code should normally depend on icydb; this crate exists for schema internals and tooling.

References:

• Workspace overview: README.md
• Contracts: docs/contracts/QUERY_CONTRACT.md, docs/contracts/IDENTITY_CONTRACT.md
• Release notes: CHANGELOG.md