x402 Facilitator with Bazaar Discovery
Problem Statement
x402 turns HTTP 402 into a machine-native payment flow, and Stellar suits it well: settlement costs about 0.0023 XLM, which is what makes per-request agent micropayments viable. Exact settlement already works (the Apache-2.0 @x402/stellar package and the free Built on Stellar facilitator), but Stellar has no native Bazaar — the discovery layer that lets an agent find, price, and pay for x402-protected services without a pre-existing integration. Today a Stellar-denominated service is only as discoverable as whichever multi-chain facilitator happens to carry it. This RFP funds a production facilitator on both networks plus a Stellar-native Bazaar, with discovery as the highest-value share of the budget.
Technical Requirements
Facilitator: verify, settle, and supported on BOTH stellar:testnet and stellar:pubnet, built on @x402/stellar rather than reimplementing settlement. Strict Soroban auth-entry validation (exact call, asset, amount, recipient; no replay; ledger-based expiration), classic keypairs and custom __check_auth accounts, any SEP-41 token with USDC default and correct 7-decimal handling, sponsored network fees advertised via extra.areFeesSponsored, and strictly non-custodial. Bazaar Discovery (the core new capability): GET /discovery/resources with the spec's filters and GET /discovery/search with REAL natural-language ranking — search quality is a graded deliverable. Automatic cataloging from the discovery extension with no separate registration step, HTTP endpoints and MCP tools as first-class resource types, catalog-integrity enforcement against forged listings including routeTemplate validation, and a commitment to track the moving x402 discovery conventions through the grant period. MCP Server: search and paid-call tools so an agent can discover and pay from inside a runtime, with machine-readable error codes on every rejection. upto Scheme Upstream: author scheme_upto_stellar.md and its implementation, contributed through the x402 Technical Steering Committee (SDF's Foundation board seat is available to unblock review). License and Conformance: a permissive OSI-approved license with no AGPL in the dependency path (the OpenZeppelin Relayer x402 plugin is AGPL and excluded as a base). Acceptance is wire-level: an unmodified canonical client completing payment end-to-end on both networks, a passing run of the x402 repo's e2e suite, and a published settled transaction hash per network per scheme. Audit: a third-party review via the Audit Bank covering the settlement path, auth-entry validation, and the discovery trust boundary before the mainnet production tag.