feat(studio): published-worktree watcher and DraftWriter API for the AI package

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

packages/feature-studio/test/watch.test.ts

@@ -0,0 +1,44 @@
+import { expect, test } from "bun:test";
+import { writeFileSync } from "node:fs";
+import { join } from "node:path";
+import { createCourseRepository } from "@stc/course-format";
+import { createPublishedWatcher } from "../src/server/watch";
+import { studioCourseDirs } from "../src/server/paths";
+import { ada, extGit, newStore } from "./helpers";
+
+test("an external commit in the published worktree reloads the CourseRepository", async () => {
+  const { dataDir, store } = await newStore();
+  const courses = await createCourseRepository(studioCourseDirs({ dataDir, courseDirs: [] }));
+  let reloads = 0;
+  const realReload = courses.reload.bind(courses);
+  courses.reload = async (id?: string) => { reloads++; await realReload(id); };
+  const w = createPublishedWatcher(store, courses, { intervalMs: 50 });
+
+  await store.createCourse({ id: "c1", title: "C" }, ada);
+  expect(await w.check()).toEqual(["c1"]); // new course, not yet loaded
+  expect(courses.get("c1")?.status).toBe("ok");
+  expect(await w.check()).toEqual([]);
+
+  const pub = store.paths("c1").published;
+  writeFileSync(join(pub, "lessons/welcome.md"), "# External\n");
+  await extGit(pub, "commit", "-qam", "external");
+  expect(await w.check()).toEqual(["c1"]);
+  expect(await courses.readLessonMarkdown("c1", "welcome")).toBe("# External\n");
+  expect(reloads).toBe(2);
+
+  // the timer path
+  writeFileSync(join(pub, "lessons/welcome.md"), "# External 2\n");
+  await extGit(pub, "commit", "-qam", "external 2");
+  w.start();
+  for (let i = 0; i < 40 && (await courses.readLessonMarkdown("c1", "welcome")) !== "# External 2\n"; i++) await Bun.sleep(25);
+  w.stop();
+  expect(await courses.readLessonMarkdown("c1", "welcome")).toBe("# External 2\n");
+});
+
+test("drafts are not discovered as courses", async () => {
+  const { dataDir, store } = await newStore();
+  await store.createCourse({ id: "c1", title: "C" }, ada);
+  await store.ensureDraft("c1", ada.id);
+  const courses = await createCourseRepository(studioCourseDirs({ dataDir, courseDirs: [] }));
+  expect(courses.list().map((c) => [c.id, c.root])).toEqual([["c1", store.paths("c1").published]]);
+});