@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.

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)