[wavekat-eason]

Docs only: adds rules to CLAUDE.md so future changes keep old clients working.

Old versions keep running after an upgrade. The platform deploys once, but devices, desktop apps and wk binaries update late or never. Consumers run whichever crate or package version they were built with.

What it asks for:

• Within a schema_version, never add additionalProperties: false or deny_unknown_fields, and new fields must be safe to ignore.
• If ignoring a field would change what a caller hears or where a call goes, bump schema_version.
• Keep conformance/v1/valid/unknown-field.yaml, which pins the tolerance, and add a corpus case for each new field.
• Before releasing a format change, parse a document using it with the oldest published crate still in use.

No code changes.