`z.json()` projects a self-referential `$defs/__schema0` entry. Twenty
tool input schemas and 123 output schemas carried it, and clients or
model APIs that reject recursive JSON Schemas refuse the whole tool
list. Every JSON value satisfies `{}`, so the shared JSON value schema
now advertises that. Runtime parsing still admits only JSON values.
Refs #919
Co-authored-by: Claude Opus 5.5 <[email protected]>
Co-authored-by: N0zoM1z0 <[email protected]>