If your systems already speak x402, AP2, UCP, Visa TAP or a card, bank or RTP rail, you connect through a registered adapter instead of a bespoke integration. Adapters run at the edge over HTTP, MCP and A2A, and none of them writes a balance. A settlement reports success only after the gateway verifies the canonical receipt the plane authority returned, so a compromised adapter cannot move your funds.

What it does

The interop workspace is a Rust workspace in interop/ whose adapters sit at the edge of Paxeer X: each one translates someone else's protocol into evidence shaped for the LayerX agent domain, and none of them writes balances. 402LXP remains the only balance writer, and custody and withdrawal guarantees stay on the Paxeer chain. layerx-interop-gateway holds the transport-neutral route set, the redaction rules and the adapter host; layerx-interop-service is the executable composition a deployment runs. It is not a second ledger.

Key capabilities

• Registered adapters x402, ap2, ucp, visa-tap, fiat and migration behind one closed route set.
• Ingress transports http, mcp and a2a; x402 buyer, seller and facilitator run on all three.
• Four evidence policies; every state-changing route must end in a receipt-verified LayerX operation.
• Portable receipt verification checks a LayerX receipt with no node, database, network or clock.
• Ethereum and Solana mirrors publish and verify batch commitments as archives, holding no custody.
• Telemetry and audit emissions carry only digests, labels, counts, durations and trace ids.

Differentiators

• An adapter descriptor cannot be declared without pinning an exact upstream specification version and the conformance suite that proves the pin, so an upstream version bump is an explicit adapter change rather than silent drift.
• The x402 adapter is pinned to x402 v2 revision 7d5363a6d51750dc246041f2b0ed5819dd46a0d7, and its local matrix shows exactly-once economic effect across HTTP, MCP and A2A under fault injection, offline over real types and a real sequencer-signed receipt. The crate states plainly that this is not upstream reference-implementation conformance and not live-service settlement.
• Eight first-party conformance suites are derived from the same vector files the adapters' own tests read, so the pinned suite is the exercised suite; no upstream publishes a suite for UCP, Visa TAP, the fiat provider callbacks or the x402 transport bindings.

Outcomes

• Connect an existing payment protocol without building a bespoke integration.
• A broken adapter cannot move funds, because adapters never write balances.
• Verify a LayerX receipt with no node, database, network or clock.

Technical notes

• layerx-agent-api is the only contract through which the interop plane reaches LayerX. A fresh gateway core holds no adapters, and an omitted or unfamiliar evidence policy refuses service startup rather than defaulting.
• Deployment inputs are explicit: a protocol network, an authoritative module registry file, a server-owned TAP clock skew of 0 to 300 seconds that is never read from a request, an active or revoked status on every trusted agent, and exactly one canonical lowercase authority and query-free path per authenticated merchant principal. Missing, unknown, revoked, expired, non-canonical and duplicate targets fail closed at startup or at request admission.
• Hosted-side authority over provider evidence: a fiat callback carries an opaque token_reference plus a signed envelope whose facts include token_reference_sha256, verified against a configured Ed25519 provider key over the domain LayerX/interop/fiat/provider-evidence/v1; AP2 bodies cannot override time, clock skew, audience, currency exponent or idempotency, and the service verifies against its own clock with zero skew. Neither surface accepts a caller-selected idempotency key, so retries converge on a key derived from the authenticated principal and the verified references.
• Migration source verifiers need two to eight independent HTTPS JSON-RPC endpoints per quorum with a strict majority, DNS names only, an independent_backend label per endpoint, absolute trust-anchor and bearer paths, and a journal head reconciled on every read and append against a strict-majority HTTPS authority. Missing, divergent, rolled-back or unauthenticated head state makes the verifier fail closed.
• There is no standalone layerx-a2a crate: A2A is a transport on the gateway and on x402, plus the installer in the developer CLI. That CLI's A2A server answers message/send, tasks/get and tasks/cancel; message/stream, tasks/resubscribe and tasks/pushNotificationConfig/set return -32004, and an unrecognised method returns -32601.
• Maturity as the repository records it: the x402, AP2, UCP, Visa TAP, fiat and portable-verification tasks are marked done, while migration tooling, the mirror publisher and verifier and the market-maker ramp toolkit are recorded as implemented with production-client or reference-service gaps, and the parent rollup tasks remain pending.

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