feat(dictionary): add Hachidori backend support

- Add backend selection, setup gating, Anki integration, and external host support
- Add launcher flags, documentation, packaging, and focused tests
- Open on-demand overlay modals on the first attempt

vendor/hachidori/extension/engine-worker-runtime.js

@@ -0,0 +1,109 @@
+/*
+ * Dedicated owner of a pthread Hoshidicts WASM runtime.
+ *
+ * The runtime lives off the browser main thread so Hoshidicts can join pthreads
+ * and WasmFS can synchronously proxy OPFS operations without deadlocking an
+ * extension page. engine-worker.js starts it on WasmFS + direct OPFS and
+ * engine-worker-idbfs.js on the classic FS + IDBFS; both call startEngineWorker.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+import {
+  configureEngineService,
+  handleEngineMessage,
+  startEngine,
+} from "./engine-service.js";
+import { boundResponseFailure } from "./response-limits.js";
+
+let nextHostRequestId = 0;
+let nextProgressId = 0;
+const HOST_REQUEST_TIMEOUT_MS = 30_000;
+const pendingHostRequests = new Map();
+const pendingProgressAcks = new Map();
+
+function describe(error) {
+  return error instanceof Error ? error.message || String(error) : String(error);
+}
+
+function requestHost(message) {
+  nextHostRequestId += 1;
+  const id = nextHostRequestId;
+  return new Promise((resolve, reject) => {
+    const timer = setTimeout(() => {
+      if (!pendingHostRequests.delete(id)) return;
+      reject(new Error("the extension host did not answer the engine worker"));
+    }, HOST_REQUEST_TIMEOUT_MS);
+    pendingHostRequests.set(id, { resolve, reject, timer });
+    globalThis.postMessage({ channel: "host-request", id, message });
+  });
+}
+
+function reportEngineProgress(progress) {
+  if (progress?.phase !== "installing") {
+    globalThis.postMessage({ channel: "engine-progress", progress });
+    return undefined;
+  }
+  nextProgressId += 1;
+  const id = nextProgressId;
+  return new Promise((resolve, reject) => {
+    const timer = setTimeout(() => {
+      if (!pendingProgressAcks.delete(id)) return;
+      reject(new Error("the extension host did not acknowledge the import lock"));
+    }, HOST_REQUEST_TIMEOUT_MS);
+    pendingProgressAcks.set(id, { resolve, reject, timer });
+    globalThis.postMessage({ channel: "engine-progress", id, progress });
+  });
+}
+
+export function startEngineWorker({ createHoshidicts, storageBackend }) {
+  configureEngineService(requestHost, {
+    createHoshidicts,
+    storageBackend,
+    lowRam: false,
+    reportProgress: reportEngineProgress,
+  });
+  startEngine();
+  // A dedicated worker receives only from its creator over its implicit
+  // MessagePort. MessageEvent.origin is always empty, so there is no origin
+  // value to validate; the channel checks in onHostMessage validate the
+  // expected protocol.
+  globalThis.onmessage = onHostMessage; // NOSONAR
+}
+
+function onHostMessage(event) {
+  const data = event.data;
+  if (data?.channel === "host-response") {
+    const pending = pendingHostRequests.get(data.id);
+    if (pending === undefined) return;
+    pendingHostRequests.delete(data.id);
+    clearTimeout(pending.timer);
+    if (data.ok === true) pending.resolve(data.response);
+    else pending.reject(new Error(data.error || "host request failed"));
+    return;
+  }
+  if (data?.channel === "engine-progress-ack") {
+    const pending = pendingProgressAcks.get(data.id);
+    if (pending === undefined) return;
+    pendingProgressAcks.delete(data.id);
+    clearTimeout(pending.timer);
+    if (data.ok === true) pending.resolve();
+    else pending.reject(new Error(data.error || "the extension host refused the import lock"));
+    return;
+  }
+  if (data?.channel !== "engine-request") return;
+
+  Promise.resolve(handleEngineMessage(data.message)).then(
+    (response) => globalThis.postMessage({ channel: "engine-response", id: data.id, response }),
+    (error) => globalThis.postMessage({
+      channel: "engine-response",
+      id: data.id,
+      response: boundResponseFailure({
+        type: `${data.message?.type || "hd_unknown"}_result`,
+        requestId: data.message?.requestId ?? null,
+        ok: false,
+        error: describe(error),
+      }),
+    }),
+  );
+}