MCP HTTP wrapper — OpenAPI contract

docs/openapi.json is a hand-written OpenAPI 3.0 document describing the HTTP surface exposed by rz mcp --http-port <addr>: GET /health and POST /mcp/call, their request/response schemas, and every status code the wrapper can return (200, 400, 404, 413, 429, 504).

It exists so external tooling (client SDK generators, contract tests, API gateways) has a machine-readable contract instead of having to read resilient/src/mcp_server.rs or the prose in MCP.md.

resilient/tests/mcp_openapi_contract_smoke.rs spawns the real rz binary and asserts that live server responses conform to the schemas in this document — the doc and the implementation are checked to stay in sync in CI.

See MCP.md for the full prose walkthrough of the MCP server, its tools, and its hardening/concurrency/logging behavior.

RES-3961. Part of the Live MCP Server initiative (#3934).