Feature Request: Native Token Metering & Bounded Overshoot (x402 Protocol)

Context

As enterprise adoption of this framework accelerates, developers are increasingly hitting the "Margin Leak" problem: autonomous agents entering loops and aggressively polling paid LLM resources without proactive financial guardrails.

Currently, developers must build bespoke token-counting wrappers around the LLM calls. If a loop occurs, the API bill skyrockets before the framework can halt it.

Proposal: Adopt the x402 Protocol

We recently authored V2 of the x402 Native Token Metering Protocol upstream in the core modelcontextprotocol repository (Issue #3229).

We propose adding native support for x402 token metering and Bounded Overshoot directly into the framework's routing layer.

How it works (Bounded Overshoot)

Instead of pre-flight token math (which leads to false refusals), the framework passes requests through a meter. If the budget is exceeded, the request returns a standardized -4020 Payment Required error, and the agent safely halts.

Visual Demonstration:

🔥 Margin Leak Simulator Running...

=============================================
🚨 SCENARIO 1: UNPROTECTED AGENT (Status Quo)
=============================================
[Unprotected] Call 1 | Cost: $0.05 | Agent continues looping blindly...
[Unprotected] Call 5 | Cost: $0.25 | Agent continues looping blindly...
[Unprotected] Call 10| Cost: $0.50 | Agent continues looping blindly...
❌ DISASTER: Agent burned $0.50 and is still looping!

=============================================
🛡️ SCENARIO 2: PROTECTED AGENT (x402 Protocol)
=============================================
[Protected] Call 1 | Cost: $0.05 | LLM Call Success.
[Protected] Call 2 | Cost: $0.10 | LLM Call Success.
[Protected] Call 3 | Cost: $0.15 | LLM Call Success.
[Protected] Call 4 | Cost: $0.20 | LLM Call Success.
[x402 Firewall] Call 5 INTERCEPTED! HTTP 402 Payment Required.
✅ SUCCESS: Agent safely halted before catastrophic margin leak.
--> Remaining Budget: $0.00

Compliance (HTTP 451)

Enterprise environments also require strict KYC/Sanctions checks. The x402 spec natively supports returning HTTP 451 (Unavailable For Legal Reasons) if a destination wallet or tool is flagged, preventing the agent from transacting with sanctioned entities.

Reference Implementation

Our team maintains the @neuforge/pay-js SDK which handles the Stripe/Fiat bridging for this exact protocol. We would love to collaborate on submitting a PR to integrate this standard routing logic natively here.

Would the maintainers be open to standardizing this guardrail?

No files, tests, or concrete entry points are named. Start by reading the framework's routing layer, upstream modelcontextprotocol issue #3229, and the @neuforge/pay-js reference SDK; done would require an agreed native x402 integration scope, bounded-overshoot behavior, and compliance handling.