Expand paid MCP tool guide

[chico10117]

Summary:

• Expand the paid MCP tool example into a reproducible guide for selling an MCP tool or API call with x402 and Pyrimid.
• Include a complete Next.js paid endpoint pattern, no-payment 402 response example, MCP tool schema, Pyrimid catalog metadata, discovery file snippet, repro checks, and common mistakes.
• Link the guide back to Pyrimid catalog, quickstart, and proof surfaces.

Bounty scope:

• MYA/Pyrimid job MYA job #20 submission: Agent Commerce Desk Pyrimid SDK integration #24: write a useful paid MCP tool guide, 10 USDC.

Validation:

• npm run build
• git diff --check

Payment requested if accepted/merged:

• Native USDC on Base
• 0x820a7bf90d944bb26bfD9b62Ab172Fc3A0829cB9

No secrets, wallet signatures, payment headers, or paid calls were used.

[egoriklok]

Free public readiness snapshot for Expand paid MCP tool guide:

• Public signal: No-payment readiness snapshot draft for Expand paid MCP tool guide #23: Expand paid MCP tool guide. Focus: api, mcp, payment, x402.
• R1 fit: api, mcp, payment, tool, wallet, x402.
• Buyer-agent check I would add before autonomous spend: explicit price/cap unit, policy/version hash, receipt or charge-evidence reference, revocation/dispute path, and allow/caution/block preflight result.
• This separates "interesting paid surface" from "safe for an agent wallet to use".

No invoice, no payment link, no delivery link, no private endpoint; this is only a free public snapshot.