Migrating to 0.7.0

0.7.0 adds direct JSON constructors, an unconstrained admitted-JSON definition, and JSON pass-through encoding. Existing definition, Contract, decoding and encoding signatures are unchanged.

• json_* constructors build opaque Json values. Fallible constructors return typed JsonError reasons. Object construction rejects duplicate keys; parsing retains its existing last-value behavior. Integer construction rejects values outside the common safe-integer range rather than rounding them.
• anything() returns a Definition(Json) that accepts every admitted JSON value unchanged. It can describe arbitrary metadata without relaxing surrounding record fields. It does not bypass admission or explicit semantic requirements.
• encoding.json() composes already admitted JSON with typed field encoders. Checked encoding and output boundaries retain their receiving Contract checks.
• to_gleam_json provides one-way conversion to the standard JSON representation. It does not expose opaque constructors or introduce a reverse admission path.

Encoding retains its existing serialization/admission path. No performance gain, source-text preservation, or decode/encode inverse is claimed. The JSON-only pass-through encoder preserves canonical JSON, including ordinary normalization of zero signs during serialization.

See Constructing JSON values and Typed JSON encoding for examples and limits.