feat: machine translation resumes after a page reload

The run is recorded at every page and picked up from the translator's finished job; one run across tabs via Web Locks.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

frontend/tests/translator-run.test.mjs

@@ -138,3 +138,39 @@ test("addresses are completed and cleaned", () => {
   assert.equal(normalizeUrl(" 127.0.0.1:8787/ "), "http://127.0.0.1:8787");
   assert.equal(normalizeUrl("https://t.example//"), "https://t.example");
 });
+
+test("a run that was interrupted picks up the page the translator finished meanwhile", async () => {
+  const server = fakeServer(["a", "b", "c", "d", "e"]);
+  const translator = fakeTranslator();
+  // the page "a","b" was sent before the reload; the translator completed it by itself
+  const sent = await translator.createJob("p", [{ id: "0", text: "a" }, { id: "1", text: "b" }]);
+  const checkpoints = [];
+  const outcome = await run(translator, server, {
+    initial: { total: 5, done: 0, failed: 0, skip: 0 },
+    resume: { jobId: sent.id, keys: ["k0", "k1"] },
+    onCheckpoint: (c) => checkpoints.push(c),
+  });
+  assert.equal(outcome, "finished");
+  assert.deepEqual(Object.keys(server.saved), ["k0", "k1", "k2", "k3", "k4"]);
+  // the first page was not sent twice: the resumed job plus two new pages
+  assert.equal(translator.created.length, 3);
+  const last = checkpoints.at(-1);
+  assert.deepEqual([last.jobId, last.done, last.failed], [null, 5, 0]);
+});
+
+test("a job the translator no longer knows is skipped and its lines come back with the list", async () => {
+  const server = fakeServer(["a", "b", "c"]);
+  const translator = { ...fakeTranslator(), async job() { throw new Error("404"); } };
+  // `job` is also used while waiting, but the resumed job fails at once, so nothing waits
+  const created = [];
+  const client = { ...translator, async createJob(...args) { const j = await fakeTranslator().createJob(...args); created.push(j); return j; } };
+  const outcome = await run(client, server, { pageSize: 3, resume: { jobId: "gone", keys: ["k0"] } });
+  assert.equal(outcome, "finished");
+  assert.deepEqual(Object.keys(server.saved), ["k0", "k1", "k2"]);
+});
+
+test("checkpoints say which page is out and when it is handled", async () => {
+  const marks = [];
+  await run(fakeTranslator(), fakeServer(["a", "b", "c"]), { pageSize: 2, onCheckpoint: (c) => marks.push([c.jobId ? "sent" : "done", c.keys.length, c.skip]) });
+  assert.deepEqual(marks, [["sent", 2, 0], ["done", 0, 0], ["sent", 1, 0], ["done", 0, 0]]);
+});