@brooswit/thatch

A central HTTP MCP server, as an Elysia plugin. Many Claude Code sessions connect to one server by URL; the server addresses them by name and can push messages into a live session.

import { Elysia } from "elysia";
import { thatch, z } from "@brooswit/thatch";

const { plugin, mcp } = thatch({
  identify: (req) => req.headers.get("x-connection-name"),   // names the connection; null rejects it
  tools: {
    status: { description: "Fleet status", input: {}, handler: (_a, c) => `hello ${c.name}` },
  },
});

const app = new Elysia().use(plugin).listen(3000);

// push a message into a named session — from anywhere
const d = await mcp.send("epic-kan-39", { content: "PR #296 approved", meta: { key: "KAN-39" } });
//  d: { claim: "C2" }  — a connected session's stream took it
//     { claim: "refused", reason: "not-connected" | "no-channel-stream" | "bad-meta" | "closed-mid-send" }

Claude Code connects with:

claude mcp add --transport http fleet http://localhost:3000/mcp --header "x-connection-name: epic-kan-39"

Why the delivery type is not void

Pushing into a session can fail in ways the MCP SDK hides: a connection can be registered while its notification stream isn't attached, in which case the SDK drops the frame silently. thatch refuses that out loud (no-channel-stream) and only claims C2 when a stream is actually there to carry the frame. C3 (entered the transcript) and C4 (the model read it) are not observable, so no API here pretends to them.

Related MCP server: agent-network

API

• thatch(options) → { plugin, mcp } — plugin mounts the endpoint (default /mcp); mcp is the handle.

• options: identify(req), onDuplicate ("replace" default | "reject"), history (default 50), tools, path, serverInfo.

• mcp.connections: list(), get(name), has(name), count(), waitFor(name, { timeoutMs }).

• mcp.send(name, frame), mcp.sendMany(names, frame), mcp.sendAll(frame, { where? }).

• mcp.on("connect" | "disconnect" | "send", handler).

• A Connection carries name, connectedAt, lastSeenAt, meta, channelReady, and history.

• import { FakeConnection } from "@brooswit/thatch/testing" for tests.

Layers

protocol (frame, delivery, method — pure) · registry (named connections + history) · channel (sending, honest claims) · plugin (the Elysia mount, one MCP server per connection) · testing.

Scripts

bun run check        # generate load tests + typecheck + unit + load + coverage ≥90%
bun test test/unit
MCP_LIVE=1 bun test test/live   # against a real Claude Code session (opt-in)