docs: remove entity wrapper from MCP response examples

[jamesandersen]

Summary

MCP response examples incorrectly nest the UCP payload under a "checkout", "cart", or "order" key inside structuredContent. Per the OpenRPC specification, the result.name field is descriptive metadata for documentation and tooling — it does not create a wrapper key in the JSON-RPC wire format. The name field only has wire-format significance on params (by-name parameter passing), not on result.

This creates an inconsistency in the current docs: error responses already place the UCP envelope directly in structuredContent (no wrapper), while success responses incorrectly wrap it.

Before (success response)

"structuredContent": {
  "checkout": {
    "ucp": { ... },
    "id": "checkout_abc123",
    ...
  }
}

After (success response — consistent with error responses)

"structuredContent": {
  "ucp": { ... },
  "id": "checkout_abc123",
  ...
}

Files changed

• docs/specification/checkout-mcp.md — 4 response examples
• docs/specification/cart-mcp.md — 6 response examples
• docs/specification/order-mcp.md — 3 response examples
• docs/specification/overview.md — 1 MCP transport example

Context

Addresses the same issue as #239, which was closed because #216 was expected to include this fix. #216 corrected error response examples but left success responses wrapped.

Checklist

• Docs only — no schema changes
• Self-reviewed
• markdownlint passes
• cspell passes
• No new warnings introduced

[alexpark20]

Good catch 👏

I think this should be merged into 04-08 release branch as well

[igrigorik]

Thanks for catching this @jamesandersen. Tracing lineage...

1. #141 introduced the wrapper when adding tools/call envelope to MCP examples -- input wrapper keys ("checkout", "cart") were copy-pasted into output structuredContent — doh.
2. #239 opened the correct fix, was closed as "resolved via #216" But 216 rewrote error response examples flat (correct) but didn't touch success responses - miss, doh again.

Once we land #359, this kind of bugs should -- hopefully -- become a thing of the past.