DF0020: Non-JSON Value in JSON-Serializable RPC

Message

RPC function "{name}" declares jsonSerializable: true but the value at "{path}" is a {type}.

Cause

A jsonSerializable: true function encodes its args and return value with strict JSON.stringify (on the wire and in build dumps). The serializer throws at the offending value rather than emit a corrupt payload when it hits anything JSON cannot round-trip losslessly:

• Map, Set, WeakMap, WeakSet
• Date (JSON coerces it to an ISO string)
• BigInt, Symbol, Function
• circular references
• non-plain class instances
• undefined leaves

Example

defineRpcFunction({
  name: 'my-plugin:graph',
  jsonSerializable: true,
  handler: () => ({
    nodes: new Map([['a', 1]]), // ✗ throws DF0020: type=Map, path="nodes"
  }),
})

Fix

Drop jsonSerializable: true to fall back to structured-clone-es (round-trips Map, Set, etc.), or convert the payload to a JSON-safe shape before returning. Keeping agent exposure requires the JSON-safe shape.

Source

• packages/devframe/src/rpc/serialization.ts: the strict JSON serializer throws DF0020 (with the offending path and runtime type) when a jsonSerializable: true payload contains a non-JSON value.