MCP gateway calls the Core Banking API over HTTP

The MCP server (mcp-gateway) owns protocol, auth, masking and audit; all domain logic and persistence live in a separate FastAPI service (core-api) reached over HTTP. We accept an extra network hop because it mirrors how an MCP layer sits in front of existing bank systems, keeps the domain usable by non-MCP clients, and gives timeouts, retries and circuit breakers a real failure boundary to protect.

Considered Options

• Tools call repositories in-process: fewer moving parts and lower latency, but resilience patterns would guard nothing real, and the domain would be welded to one protocol.