Crate klieo_mcp_server 

Expose any klieo ToolInvoker as an MCP server over stdio or HTTP (see the http cargo feature).

This crate is the inverse of klieo-tools-mcp: instead of a Rust host calling external MCP servers, it lets external MCP hosts (Claude Desktop, Continue, LangGraph, OpenAI Agents SDK) call into a Rust-built klieo ToolInvoker.

Polyglot strategy: klieo exposes three wire-level contracts so non-Rust hosts can integrate without depending on klieo crates — the NATS bus (durable pipelines), this MCP server (stdio/HTTP tool calls), and the A2A peer protocol (JSON-RPC). This crate covers the MCP-server contract.

Scope

• stdio transport — newline-delimited JSON-RPC 2.0 frames on stdin/stdout, matching the MCP reference spec.
• tools/list — derived from the invoker’s catalogue.
• tools/call — dispatches to ToolInvoker::invoke with a ToolCtx minted per request from the McpServerBuilder::with_tool_ctx_factory-supplied factory. Default factory is the in-memory noop wiring (Pubsub/KvStore/ JobQueue from klieo-bus-memory, fresh per call). Override the factory to expose tools that need real bus access.
• initialize / shutdown — standard MCP handshake.

Out-of-scope:

• SSE streaming responses (HTTP transport returns JSON only).
• Multi-tenant auth (wrap router() with a tower auth layer, or front with an auth-enforcing reverse proxy).

Agent exposure (0.9, ADR-010)

McpServer::expose_agent_with_schema(agent, schema, ctx_factory) wraps any klieo_core::Agent as a single MCP tool whose inputSchema is the caller-supplied JSON Schema. The ctx_factory closure is called per tools/call to mint a fresh klieo_core::agent::AgentContext (so each invocation gets its own RunId).

Behind the schemars cargo feature, expose_agent::<A>(agent, ctx_factory) derives the schema automatically via schema_for!(A::Input). See ADR-010 for the trade-off.

Re-exports

pub use outbound_sink::OutboundFrameSink;

pub use outbound_sink::OutboundSinkError;

pub use sampling::ModelHint;

pub use sampling::ModelPreferences;

pub use sampling::SamplingContent;

pub use sampling::SamplingMessage;

pub use sampling::SamplingRequest;

pub use sampling::SamplingResponse;

pub use roots::Root;

pub use outbound_ext::McpOutboundExt;

pub use outbound_sink::bench_stdio_sink;

Modules

outbound_ext

Typed extension methods over klieo_core::ServerOutbound.

outbound_sink

Per-transport frame-write abstraction over JSON-RPC envelopes.

roots

MCP roots — client-declared URI scopes the server may operate on.

sampling

MCP sampling/createMessage wire-format types.

Structs

McpServer

MCP server that exposes a klieo-core ToolInvoker as a stdio MCP server.

McpServerBuilder

Builder for McpServer. Collects one or more invokers (raw ToolInvokers or Agents wrapped as single-tool invokers) and configures server-level concerns such as transports, parent cancel, leader election, tenant binding, and authentication.

Enums

McpBuildError

Errors returned by McpServerBuilder::build and McpServerBuilder::build_arc.

McpServerError

Top-level error from the MCP server loop.

OrphanOutcome

Re-export the cluster-0.24 follower-side orphan re-invoke gate for integration tests. Gated on test-fixtures so production callers cannot reach the helper. See crate::http::OrphanOutcome

Constants

LEADER_TTL

Leader-claim TTL for the klieo-leaders KV bucket used by stream_tools_call (claim on invoke) and stream_resume (orphan check on resume). Operators MUST configure the JetStream KV bucket with max_age equal to this value so a dead replica’s leader entry evicts automatically; the registry’s heartbeat runs every TTL / 2. See ADR-020.

MCP_LEADER_KEY_PREFIX

Leader-key prefix for the MCP transport in the shared klieo-leaders bucket. Mirrors a2a.<task_id> on the A2A side.

MCP_PROTOCOL_VERSION

MCP protocol revision advertised on every initialize response.

Functions

bench_filter_replay

Scans a replay-buffer snapshot and returns entries with event_id > since_id. Approximates the per-frame scan cost of the SSE replay path without HTTP header parsing or lock acquisition overhead. Available only under the bench feature.

encode_sse_frame

Encodes one SSE frame into a Bytes buffer: id: <N>\ndata: <json>\n\n.

handle_dead_leader_orphan_mcp

Re-export the cluster-0.24 follower-side orphan re-invoke gate for integration tests. Gated on test-fixtures so production callers cannot reach the helper. See crate::http::OrphanOutcome

Type Aliases

AgentContextFactory

Factory for fresh klieo_core::agent::AgentContext values, called once per tools/call so each invocation gets its own RunId + cancel token. Caller-owned to keep klieo-mcp-server free of opinions about which memory / bus / llm backends an agent runs against.

ToolCtxFactory

Factory for fresh klieo_core::tool::ToolCtx values, called once per tools/call so each invocation gets its own Pubsub / KvStore / JobQueue (or a shared one, caller’s choice). Default = default_tool_ctx_factory which mints the same per-request in-memory wiring serve_stdio has used since 0.8. Override via McpServerBuilder::with_tool_ctx_factory to expose bus-using tools through this server.