Do not make the ingest folder

A folder that Bindery made hid a missing volume mount. The books went
to a folder inside the container, and CWA never saw them. A missing
folder is now an error in the log at the start, and each upload fails
with a message that names the mount.

tests/test_cwa.py

@@ -9,7 +9,7 @@ from test_build import URL, chapters, metahtml
 from bindery import fff
 from bindery.cwa import BookFinder, CwaClient, CwaError, plain_title, search_text, title_rank
 from bindery.epub import epub_metadata, epub_urls
-from bindery.ingest import MAX_NAME_LENGTH, IngestFolder
+from bindery.ingest import MAX_NAME_LENGTH, IngestError, IngestFolder
 
 STORY_URL = "https://www.royalroad.com/fiction/1234"
 
@@ -187,6 +187,7 @@ def test_epub_reader(story_epub, tmp_path):
 
 def test_ingest_uses_part_names_and_unique_names(tmp_path):
     folder = IngestFolder(tmp_path / "ingest")
+    folder.path.mkdir()
     epub = tmp_path / "x.epub"
     epub.write_bytes(b"PK")
     first = folder.ingest(epub, 'A: "Story" / Name')
@@ -198,6 +199,7 @@ def test_ingest_uses_part_names_and_unique_names(tmp_path):
 
 def test_send_update_writes_sidecar(tmp_path):
     folder = IngestFolder(tmp_path / "ingest")
+    folder.path.mkdir()
     epub = tmp_path / "x.epub"
     epub.write_bytes(b"PK")
     path = folder.send_update(epub, 7, "T" * 300)
@@ -206,3 +208,13 @@ def test_send_update_writes_sidecar(tmp_path):
     manifest = json.loads((folder.path / (path.name + ".cwa.json")).read_text())
     assert manifest == {"action": "add_format", "book_id": 7}
     assert path.read_bytes() == b"PK"
+
+
+def test_a_missing_ingest_folder_is_an_error_and_is_not_made(tmp_path, story_epub):
+    source = tmp_path / "book.epub"
+    source.write_bytes(story_epub)
+    folder = IngestFolder(tmp_path / "missing" / "ingest")
+    for send in (lambda: folder.ingest(source, "Title"), lambda: folder.send_update(source, 5, "Title")):
+        with pytest.raises(IngestError, match="does not exist. Check INGEST_DIR and the volume mount."):
+            send()
+    assert not (tmp_path / "missing").exists()