fix(import): name merged parts after their folder and clean up empty ones

tests/test_import_flow.py

@@ -504,3 +504,37 @@ def test_merge_at_download_root_keeps_the_download_dir(client):
     assert res["ok"], res
     assert client.downloads.is_dir()
     assert not (client.downloads / "Teil 1").exists()
+
+
+def test_merged_parts_clean_up_nested_source_folders(client):
+    """"100 - Toteninsel/A - Sphinx/CD/*.mp3" - every emptied level below the
+    merged item goes away, the cover folder keeps its parent alive."""
+    lib_id = client.post("/api/libraries", json={
+        "name": "L", "media_type": "audiobook", "root_path": str(client.tmp_path / "l"),
+        "folder_template": "{Title}", "file_template": "{Title}",
+    }).json()["id"]
+    req_id = client.post("/api/requests",
+                         json={"library_id": lib_id, "title": "Toteninsel"}).json()["id"]
+
+    base = client.downloads / "100 - Toteninsel"
+    files = []
+    for part in ("A - Sphinx", "B - Volk", "C - Graeber"):
+        cd = base / part / "CD"
+        cd.mkdir(parents=True)
+        for i in (1, 2):
+            f = cd / f"{i:02d}.mp3"
+            f.write_bytes(b"")
+            files.append(str(f))
+    (base / "Cover").mkdir()
+    (base / "Cover" / "front.jpg").write_bytes(b"")
+
+    res = client.post("/api/import", json={"items": [{
+        "path": str(base), "is_dir": True, "files": files, "request_id": req_id,
+    }]}).json()["results"][0]
+    assert res["ok"], res
+    assert sorted(p.name for p in Path(res["dest"]).iterdir()) == [
+        f"Toteninsel - Part 0{i}.mp3" for i in range(1, 7)
+    ]
+    assert not (base / "A - Sphinx").exists()
+    assert not (base / "B - Volk").exists()
+    assert (base / "Cover" / "front.jpg").exists()