perf: keep heavy work off UI thread

web/ocs-parse-worker.js

@@ -0,0 +1,20 @@
+import init, { parse_document } from "./worker_pkg/ocs_web_worker.js";
+
+const ready = init();
+
+self.onmessage = async ({ data }) => {
+  try {
+    await ready;
+    const encoded = parse_document(data.name, new Uint8Array(data.bytes));
+    // wasm-bindgen returns a view into WebAssembly.Memory. Copy to a standalone
+    // ArrayBuffer before transferring it, otherwise the worker's wasm memory
+    // itself would be detached.
+    const transferable = encoded.slice();
+    self.postMessage({ ok: true, data: transferable.buffer }, [transferable.buffer]);
+  } catch (error) {
+    self.postMessage({
+      ok: false,
+      error: error instanceof Error ? error.message : String(error),
+    });
+  }
+};