PATH Protocol

Why

PATH FINDER reaches destinations held by PATH members. Most destinations are held elsewhere: in the Pix DICT, in the PI-SPI alias directory, in UPI, behind SEPA Verification of Payee. An address may declare that its subject receives on one of those rails (PIP-0003). The PATH resolver then stops at what the holder declared.

A payer that wants to confirm the key in the external registry, learn the participant holding it, or check the name, today integrates each registry separately, through whoever holds access to it. This PIP names one interface for that, and the rules that keep it from turning PATH into a directory of other networks' accounts.

What it is

Stage	Question	Answered by
Discovery	Which external registry can know this key?	The form of the key and the connector register. No registry is queried
SONAR	Does that registry hold it, and at which participant?	The registry, through an attested connector
RESOLVER	Where to send, on which rail, in which currency?	The registry, through an attested connector
Payee check	Is it the person I think?	The registry's own name check, in the two modes of [PIP-0013](/pips/0013)

SONAR and RESOLVER together are the Crossway Finder, composed as PATH FINDER is.

What it is not

Not a rail. No value moves through Crossway. Payment executes and settles on the external rail, initiated by the payer's own provider.
Not a pillar. It adds no object to the five pillars.
Not a directory. A connector stores no registry entry beyond the answer that carried it.
Not a resolver answer. A Crossway answer reports a registry's entry. It carries no standing and no commitment. It is not a `gateway` answer: a gateway offers its own terms to carry a payment; Crossway offers none.

Entry

Crossway takes an external key: a phone number, an email, a tax number, a random key, an alias, an IBAN, a VPA. It never takes a PATH address. A caller starting from a PATH address resolves it with PATH FINDER first, and passes the external key named by the payment instruction.

Registries

A registry is named <rail>.<registry>, with the rail from the register.

id	Network	Zone	Operations
`pix.dict`	Pix, Diretório de Identificadores de Contas Transacionais	BR	sonar, resolver, payee_check
`pi-spi.alias`	PI-SPI alias directory	UEMOA	sonar, resolver, payee_check
`upi.vpa`	UPI virtual payment addresses	IN	sonar, resolver, payee_check
`sepa-inst.vop`	SEPA Verification of Payee	SEPA	payee_check

On approval, this PIP adds pi-spi (PI-SPI, UEMOA, instant, XOF) to the rail register as reserved. Until then pi-spi names a registry here, not a rail a capability may take.

Trust

Each answer is signed by the connector that read the registry. Each connector holds a crossway.connector_attestation, signed by the operator of the Crossway service, naming the registry, the operations, the access under which it reads, and an expiry. A caller verifies both signatures and checks the attestation at read. An answer whose attestation does not cover that registry and that operation is discarded.

Rules

Discovery never queries a registry. A candidate is a possibility, never an existence.
SONAR answers are constant-shape: unknown and not visible are the same response.
Calls are server-side, bound to purpose: payment_preparation, budgeted per client and per registry, and logged with the key hashed.
There is no batch operation.
Where the external scheme's rules are stricter, they apply.
No answer returns a subject's other identifiers.

Operator

The interface is specified here. The Crossway API is operated by Path Global, a private company, with access granted on request at pathglobal.finance. Registry access is obtained through authorised participants of each network, and partners.

Implementation

CrosswayClient and verifyCrosswayAnswer in @pathprotocol/sdk 0.3.0. crossway_registries, crossway_discovery, crossway_finder, crossway_payee_check and crossway_verify in the API MCP server. The API at api.pathglobal.finance/crossway/v1, operated by Path Global. Registries open one at a time; GET /registries states which.

Compatibility

Additive. Nothing in the pillars, FINDER or the resolver answer changes.