Local harness MCP bridge

Import startHarnessMcpBridge from @uppercut-labs/agent-native/harness/mcp-bridge in Node 22+. It serves an application-supplied Web Request/Response MCP handler on 127.0.0.1 at /mcp, using an ephemeral port by default. It refuses public binds and validates Host/Origin, preserving handler authentication and capability authorization. It does not import the MCP SDK or mint credentials.

const bridge = await startHarnessMcpBridge({ handler: applicationMcpHandler });
try {
  // Configure the local provider to connect to bridge.url.
} finally {
  await bridge.close();
}

port may be 0-65535. maxRequestBytes defaults to 32768 (1-1048576), and deadlineMs defaults to 30000 (1-300000), including response streaming. Oversized requests receive 413; deadlines abort the request and return 504 before headers or close an already streaming response. Handler errors produce a fixed diagnostic and 500 or stream closure. Handlers must honor AbortSignal to release their own work. Idempotent close() aborts active requests and closes only owned connections.

Loopback is reachable by local processes and is not an authorization grant. Anonymous MCP initialization may succeed while protected calls stay denied. Application policy remains authoritative at discovery and execution. Cloud agents need a caller-supplied reachable authenticated endpoint; this helper never creates a public bind or tunnel. See MCP policy and harness contracts.