[DRAFT] Add agentic facilitator module (x402)

[Dominik1999]

Add an optional Guardian module that acts as an x402 payment facilitator. This module would allow the Guardian to participate in x402-compliant payment flows on behalf of its users.

Design is intentionally open at this stage — this issue tracks the requirement and will be refined as the x402 spec and integration needs become clearer.

Parent: [DRAFT] Modularization (#251)

[peterxing]

I turned this draft into a threat-model-first readback so the module boundary has something concrete to react to before any live facilitator credentials or private-account authority enter the design:

https://farmbot-platform-mvp.pages.dev/hire-agent/openzeppelin-guardian-x402-facilitator-readback/

The safe first shape I’d suggest:

• keep the x402 facilitator as an opt-in middleware module, disabled by default;
• split lifecycle hooks into quote → pre-authorization → verify → settle → receipt → audit append;
• gate every path with per-account caps, resource allow-lists, chain/token allow-lists, expiry, replay protection, and user-visible approval state;
• bind receipts to Guardian account id, delta/proposal id, resource URL/hash, facilitator response, payment/tx hash when available, and canonical audit timestamp;
• start with mocked 402/verify/settle fixtures and fail-closed tests before any live facilitator adapter.

I’d price a focused readiness packet at A$690, or a mocked implementation room at A$2,400 if you want the Rust/TS interfaces + tests + docs split into maintainer-ready PRs. Contact: info@transhumanism.com.au; USDC on Base/Polygon or invoice after scope confirmation.