Python: feat(middleware): add agentpay-mcp payment governance middleware example

[up2itnow0822]

Summary

Adds a new middleware sample (payment_governance_middleware.py) demonstrating how to enforce spend governance on AI agent tool calls using agentpay-mcp.

Problem

Agent Framework ships a rich middleware system with examples for logging, security, usage tracking, and shared state — but no example for payment governance. As agents gain the ability to make paid API calls (via x402 or other payment protocols), operators need middleware that enforces budget limits before money leaves the wallet.

AI gateways (LiteLLM, Portkey) govern inference costs. Nothing in the current samples governs outbound agent spending.

Solution

A function-based middleware that enforces three gates before every paid tool call:

1. Per-call limit — no single payment exceeds a threshold
2. Session cap — total session spend stays within budget
3. Category cap — independent limits per spending category (data, compute, services)

The sample follows the existing middleware patterns (same imports, same structure as usage_tracking_middleware.py) and runs standalone with uv run.

Why agentpay-mcp

• Drop-in MCP server for x402 payments on Base (USDC)
• 475 weekly npm downloads
• Merged into NVIDIA NeMo Agent Toolkit Examples (PR #17) as an official catalog entry
• MIT licensed

Changes

• python/samples/02-agents/middleware/payment_governance_middleware.py — new sample
• python/samples/02-agents/middleware/README.md — added table entry

[up2itnow0822]

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