fix(course-format): validate anchor file via requireFile; real throw test for loadCourse catch

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

packages/course-format/src/load.ts

@@ -138,7 +138,16 @@ async function loadCourseUnsafe(manifestPath: string): Promise<LoadedCourse> {
     return mdCache.get(abs)!;
   };
   /** Reports an error and returns false when `rel` is not a regular file (or directory, if asked) inside the root. */
+  const checked = new Map<string, boolean>(); // one diagnostic per (lesson, path)
   const requireFile = (rel: string, what: string, lessonId?: string, dir = false): boolean => {
+    const key = `${lessonId ?? ""}\0${rel}\0${dir}`;
+    const prior = checked.get(key);
+    if (prior !== undefined) return prior;
+    const ok = checkFile(rel, what, lessonId, dir);
+    checked.set(key, ok);
+    return ok;
+  };
+  const checkFile = (rel: string, what: string, lessonId: string | undefined, dir: boolean): boolean => {
     const abs = resolveInside(root, rel);
     if (!abs) {
       err(`${what} not found: ${rel}`, { lessonId, path: rel });
@@ -174,7 +183,7 @@ async function loadCourseUnsafe(manifestPath: string): Promise<LoadedCourse> {
         const file = l.file ?? l.hints?.file;
         if (!file) {
           err(`anchor "${l.anchor}" given but the lesson has no file`, { lessonId: id });
-        } else if (fileOk) {
+        } else if (fileOk && requireFile(file, l.file ? "lesson file" : "hints file", id)) {
           const md = await readMd(file);
           if (md !== null && extractSection(md, l.anchor) === null) {
             err(`anchor "${l.anchor}" not found in ${file}`, { lessonId: id, path: file });

packages/course-format/test/load.test.ts

@@ -1,5 +1,5 @@
 import { afterAll, describe, expect, test } from "bun:test";
-import { mkdtemp, rm, symlink } from "node:fs/promises";
+import { chmod, mkdtemp, rm, symlink } from "node:fs/promises";
 import { tmpdir } from "node:os";
 import { join, resolve } from "node:path";
 import { createCourseRepository, discoverManifests, loadAll, loadCourse } from "../src/index";
@@ -92,20 +92,38 @@ describe("overlays and errors", () => {
     expect(e[0]!.path).toBe("adir");
   });
 
-  test("one throwing course does not break loadAll", async () => {
+  test("anchor resolved through a hints.file directory (no lesson file) gives one lesson diagnostic and loading continues", async () => {
+    const d = await tmp();
+    await Bun.write(join(d, "adir/x.md"), "# X\n");
+    const lessons = [
+      "      - { id: via-hints, title: L, type: exercise, anchor: sec, hints: { file: adir, match: 'E' } }",
+      "      - { id: after, title: L, type: text, file: missing.md }",
+    ].join("\n");
+    await Bun.write(join(d, "stcourse.yaml"), manifest("dirs2", "", lessons));
+    const c = await loadCourse(join(d, "stcourse.yaml"));
+    const e = c.diagnostics.filter((x) => x.level === "error");
+    expect(e.map((x) => x.lessonId)).toEqual(["via-hints", "after"]);
+    expect(e[0]!.path).toBe("adir");
+  });
+
+  // An unreadable file passes requireFile (it is a regular file) but Bun.file().text() rejects.
+  test.skipIf(process.getuid?.() === 0)("one throwing course does not break loadAll", async () => {
     const d = await tmp();
-    await Bun.write(join(d, "bad/adir/x.md"), "# X\n");
     await Bun.write(join(d, "bad/a.md"), "# A\n## Sec\n");
-    await Bun.write(
-      join(d, "bad/stcourse.yaml"),
-      manifest("bad", "", "      - { id: h, title: L, type: exercise, file: a.md, hints: { file: adir, match: 'E' } }"),
-    );
+    await chmod(join(d, "bad/a.md"), 0o000);
+    await Bun.write(join(d, "bad/stcourse.yaml"), manifest("bad", "", "      - { id: l, title: L, type: text, file: a.md, anchor: sec }"));
     await Bun.write(join(d, "good/a.md"), "# A\n");
     await Bun.write(join(d, "good/stcourse.yaml"), manifest("good", "", "      - { id: l, title: L, type: text, file: a.md }"));
-    const all = await loadAll([d]);
-    expect(all.map((c) => c.id).sort()).toEqual(["bad", "good"]);
-    expect(all.find((c) => c.id === "bad")!.status).toBe("error");
-    expect(all.find((c) => c.id === "good")!.status).toBe("ok");
+    try {
+      const all = await loadAll([d]);
+      expect(all.map((c) => c.id).sort()).toEqual(["bad", "good"]);
+      const bad = all.find((c) => c.id === "bad")!;
+      expect(bad.status).toBe("error");
+      expect(bad.diagnostics[0]!.message).toContain("unexpected error");
+      expect(all.find((c) => c.id === "good")!.status).toBe("ok");
+    } finally {
+      await chmod(join(d, "bad/a.md"), 0o644);
+    }
   });
 
   test("invalid manifest gives an error course and does not throw", async () => {