lsp-mcp: headless-editor MCP server over a language server

Effect 4 MCP server (stdio/HTTP) bridging one LSP process: on-demand document
sync with LRU and disk change detection, push/pull diagnostics reconciliation,
capability-gated tools, diagnostics resources, tests against a fixture server.

src/Server.ts

@@ -0,0 +1,69 @@
+/**
+ * Wires the language server, the headless editor and the MCP server together.
+ *
+ * Build order matters: the language server initializes first (so tool
+ * registration can consult its capabilities), then the editor services, then
+ * the MCP transport, then tools and resources are registered.
+ */
+import { createServer } from "node:http";
+import { NodeHttpServer } from "@effect/platform-node";
+import { Effect, Layer } from "effect";
+import { McpProtocol, McpServer } from "effect/unstable/ai";
+import { HttpRouter } from "effect/unstable/http";
+import { Diagnostics } from "./lsp/Diagnostics.ts";
+import * as Documents from "./lsp/Documents.ts";
+import * as LanguageServer from "./lsp/LanguageServer.ts";
+import * as Resources from "./Resources.ts";
+import * as Tools from "./Tools.ts";
+
+export type Transport =
+  | { readonly _tag: "stdio" }
+  | { readonly _tag: "http"; readonly port: number };
+
+export interface Options {
+  readonly transport: Transport;
+  readonly server: LanguageServer.Options;
+  readonly documents: Documents.Options;
+}
+
+const info = {
+  name: "lsp-mcp",
+  version: "0.1.0",
+  protocols: [
+    McpProtocol.v2025_11_25,
+    McpProtocol.v2025_06_18,
+    McpProtocol.v2025_03_26,
+    McpProtocol.v2024_11_05,
+  ],
+} as const;
+
+const transport = (transport: Transport) =>
+  transport._tag === "stdio"
+    ? McpServer.layerStdio(info)
+    : HttpRouter.serve(McpServer.layerHttp({ ...info, path: "/mcp" }), {
+        disableLogger: true,
+      }).pipe(
+        Layer.provide(
+          NodeHttpServer.layer(createServer, { port: transport.port }),
+        ),
+      );
+
+/** Registers the tools the connected server can serve. */
+export const tools = Layer.effectDiscard(
+  Effect.gen(function* () {
+    const { capabilities } = yield* LanguageServer.LanguageServer;
+    yield* McpServer.registerToolkit(Tools.supportedBy(capabilities));
+  }),
+).pipe(Layer.provide(Tools.layer));
+
+export const layer = (options: Options) =>
+  Layer.mergeAll(tools, Resources.layer).pipe(
+    Layer.provide(transport(options.transport)),
+    Layer.provide(
+      Layer.mergeAll(
+        Documents.Documents.layer(options.documents),
+        Diagnostics.layer,
+      ),
+    ),
+    Layer.provide(LanguageServer.LanguageServer.layer(options.server)),
+  );