How does the Runtime integrate with external systems like banks or blockchains? What is a "connector"?

Connectors are a family of backend integration services that sit at the boundary between the Runtime and the outside world — HTTP, Blockchain, and Wallet connectors being the main ones.

The Runtime deliberately does no blocking input/output during transaction processing, so all talking-to-the-outside is delegated to connectors:

• HTTP Connector — the preferred route for generic REST-based external systems (Representational State Transfer, the usual style of web APIs). It listens for AMQP notifications from NPL, makes the matching external API call, and then calls back into the Runtime by invoking an NPL permission or obligation — feeding the response back as a real action.
• Blockchain Connector — for interacting with blockchains.
• Wallet Connector — for wallet/key operations.

A connector is thus bidirectional: NPL notification goes out → external call is made → result is delivered back in as a callback. It is the clean seam where an otherwise self-contained protocol meets messy external systems.