Challenge 2: Write a JSON-RPC Request/Response Pair — Possible Solution
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// Request
{
  "jsonrpc": "2.0",
  "method": "add",
  "params": [7, 5],
  "id": 42
}

// Response
{
  "jsonrpc": "2.0",
  "result": 12,
  "id": 42
}

WHY THIS WORKS AS AN ANSWER
------------------------------
Every part of the JSON-RPC 2.0 spec shown in the chapter is present
and used correctly:
  - "jsonrpc": "2.0" appears in both the request and response,
    declaring which version of the spec is being followed.
  - "method": "add" names the procedure being called.
  - "params": [7, 5] supplies the two numbers as an ordered list of
    arguments, matching how the chapter's "subtract" example passed
    its two numbers.
  - "id": 42 appears in BOTH the request and the response with the
    SAME value — this is the detail the challenge specifically
    called out, and it's what lets a client match this particular
    response back to this particular request, especially important
    if several requests were sent before their responses come back
    (which is exactly why the spec requires it rather than treating
    it as optional).
  - "result": 12 is the actual answer (7 + 5), replacing "params" in
    the response the same way the chapter's example replaced it with
    "result": 19 for the subtraction call.