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.

test/fixtures/workspace.ts

@@ -0,0 +1,23 @@
+import { fileURLToPath } from "node:url";
+import { Effect, FileSystem, Layer, Path } from "effect";
+import { LanguageServer } from "../../src/lsp/LanguageServer.ts";
+
+const server = fileURLToPath(new URL("./server.ts", import.meta.url));
+
+/** A temporary workspace with the given files, served by the fixture language server. */
+export const workspace = (files: Record<string, string>) =>
+  Layer.unwrap(
+    Effect.gen(function* () {
+      const fs = yield* FileSystem.FileSystem;
+      const path = yield* Path.Path;
+      const root = yield* fs.makeTempDirectoryScoped({ prefix: "lsp-mcp-" });
+      for (const [name, content] of Object.entries(files)) {
+        yield* fs.writeFileString(path.join(root, name), content);
+      }
+      return LanguageServer.layer({
+        command: process.execPath,
+        args: [server],
+        root,
+      });
+    }),
+  );