Render compose batch pages that have no id as one page each

Pages without an id get the default id page-N from the parser, but the
batch's page lookup matched only explicit ids, so every page rendered the
whole deck and the contact sheet then failed with "Invalid URL". The lookup
now matches a page without an id by its position.

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

Author: gersham

src/compose/batch.ts

@@ -55,8 +55,10 @@ function pageSource(input: unknown, pageId: string): unknown {
   if (!input || typeof input !== "object" || Array.isArray(input)) return input;
   const record = input as Record<string, unknown>;
   if (!Array.isArray(record.pages)) return input;
-  const match = record.pages.find((item) => (
-    item && typeof item === "object" && !Array.isArray(item) && (item as { id?: string }).id === pageId
+  // A page without an id has the default id the parser gives it: page-N, by position.
+  const match = record.pages.find((item, index) => (
+    item && typeof item === "object" && !Array.isArray(item)
+      && ((item as { id?: unknown }).id == null ? pageId === `page-${index + 1}` : (item as { id?: string }).id === pageId)
   ));
   if (!match || typeof match !== "object" || Array.isArray(match)) return input;
   const { pages: _pages, ...rails } = record;

src/compose/compose.test.ts

@@ -441,6 +441,29 @@ test("compose batch contact-sheet and --only use the same engine", async () => {
   await rm(dir, { recursive: true, force: true });
 });
 
+test("compose batch renders pages without ids one page each, with a contact sheet", async () => {
+  const dir = await testTemp("compose-batch-noid-");
+  const input = path.join(dir, "deck.json");
+  await writeFile(input, JSON.stringify({
+    width: 320,
+    height: 180,
+    background: "#111111",
+    text: "#eeeeee",
+    pages: [{ left: { title: "One" } }, { left: { title: "Two" } }],
+  }));
+  const output = path.join(dir, "rendered");
+  const result = await composeBatch(input, output);
+  assert.equal(result.rendered, 2);
+  assert.equal(result.failed, 0);
+  assert.deepEqual(result.pages.map((page) => page.id), ["page-1", "page-2"]);
+  for (const id of ["page-1", "page-2"]) {
+    assert.equal(existsSync(path.join(output, id, "manifest.json")), true);
+    assert.equal(existsSync(path.join(output, id, "page-1")), false, "a page renders itself, not the whole deck");
+  }
+  assert.ok((await readFile(result.preview)).subarray(0, 8).equals(PNG_HEADER));
+  await rm(dir, { recursive: true, force: true });
+});
+
 test("compose batch continues after one page image fails", async () => {
   const dir = await testTemp("compose-batch-fail-");
   const input = path.join(dir, "deck.json");