Which package(s) are affected?

@aws-blocks/core

Describe the bug

parseRpcRequest() accepts primitive JSON-RPC params values even though JSON-RPC 2.0 requires params, when present, to be a structured value (an array or object).

The parser currently uses:

args: Array.isArray(parsed.params)
  ? parsed.params
  : Object.values(parsed.params ?? {}),

As a result:

• params: "abc" is accepted as args: ["a", "b", "c"]
• params: 42 is accepted as args: []
• params: true is accepted as args: []
• params: null is accepted as args: []

This can turn a malformed request from a hand-written HTTP or generated native client into a valid method invocation with unexpected arguments. RpcErrorCode.InvalidParams (-32602) is already defined, but no parser path currently emits it.

Expected behavior

• Array params remain positional arguments.
• Object params remain named arguments, using the existing value-order behavior.
• Omitted params continue to mean no arguments.
• Primitive or null params return a JSON-RPC error response with code -32602 and preserve the request id.

Reproduction steps

On current main (a1de3b8), call:

parseRpcRequest(JSON.stringify({
  jsonrpc: "2.0",
  method: "api.echo",
  params: "abc",
  id: 1,
}));

Actual result:

{
  "ok": true,
  "request": {
    "apiNamespace": "api",
    "method": "echo",
    "args": ["a", "b", "c"],
    "id": 1
  }
}

The same request with params: 42, true, or null is also accepted with an empty args array.

Suggested fix

Validate params before converting it to arguments. If the property is present, require an array or non-null object; otherwise return RpcErrorCode.InvalidParams with a structured InvalidParams error name. Add focused unit tests covering accepted array/object/omitted values and rejected primitive/null values.

Additional context

I searched existing open and closed issues and pull requests for InvalidParams, parseRpcRequest, and JSON-RPC parameter validation and did not find an existing report or implementation.