mcp-server

Minimal MCP server helpers (EXPERIMENTAL x/ tier, #6 Y1; stream 18) — the server counterpart to cx-x/mcp, at the 2025-06-18 protocol revision (one target). Pure request readers (method-of, id-of, tool-name-of, tool-args-of) + response builders (initialize-result, tools-list-result, tool-result, tool-error, protocol-error) composed from cx-stdlib/jsonrpc + json. tools/list derives from module source at list time via cx-x/tools (tool-json-of maps one descriptor to the MCP entry with outputSchema, annotation hints, and _meta carrying the Tier-1/Tier-2 addresses, schema ids, and cap: requirements; tools-for maps a whole module — a projection failure propagates, never a silent empty list). The tools/call boundary is PROPOSE-ONLY: propose-call / propose-result construct the cx:propose proposal and reply with its canonical text + Tier-1 address (what an out-of-band approval binds) — the command body never runs on this path. The differentiator (ties #7's PEP): a tool handler is ordinary CX, so its effects are gated by CX capabilities at the effect point — a denied effect (CXER0271) maps to an isError tool result. The transport is the real cx-stdlib/http server: a [?def] handler reads the request, dispatches on the method, and returns a [response].

Experimental x/ tier — imported as cx-x/mcp-server. Bundled and gated in-tree like any other module, but EXEMPT from the frozen-surface stability promise (std-lib README, decision D3): a semver-breaking change is allowed here while the surface settles, and the frozen-surface canary never counts it. Pin behaviour you depend on with your own fixtures.