feat: Cleanup can import files that are on disk but not in the library

A download writes its files into the artist's folder and imports them in a
later step. A run that stopped in between left complete files no record
points at, and a walk that had already marked them seen never returned for
them; on the live instance that is about 95 GB of art.

"Import files the library is missing" (Cleanup, Duplicates & leftovers)
walks every folder named for an artist, matched by slug so a differently
cased folder still matches, and lists the images, videos and archives no
image, attachment or queued import points at. Stores, sidecars, staging
files and files changed in the last day are left alone. Preview shows the
counts per artist; Import queues the same list as a library import batch,
whose tasks file the folder's post record, attach each file where it lies
with its folder's artist and source, and remove the ones the library
already holds or the import filters reject. A file whose import crashed is
kept.

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

tests/test_library_scan.py

@@ -0,0 +1,123 @@
+"""Finding files in the artists' folders that the library has no record of, and
+importing them where they lie (services.library_scan + the `library` batch)."""
+
+import io
+import os
+import time
+
+import pytest
+from PIL import Image
+from sqlalchemy import select
+
+import backend.app.tasks.import_file as import_file
+from backend.app.models import Artist, ImageRecord, ImportSettings, ImportTask
+from backend.app.services import library_scan
+from backend.app.services.importer import Importer
+from backend.app.services.thumbnailer import Thumbnailer
+
+pytestmark = pytest.mark.integration
+
+
+def _jpeg(seed: int) -> bytes:
+    im = Image.new("RGB", (256, 256))
+    px = im.load()
+    for y in range(256):
+        for x in range(256):
+            px[x, y] = ((x * seed) % 256, (y * (seed + 1)) % 256, (x ^ y) % 256)
+    buf = io.BytesIO()
+    im.save(buf, "JPEG")
+    return buf.getvalue()
+
+
+def _write(path, data: bytes, *, age_days: float = 2):
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_bytes(data)
+    t = time.time() - age_days * 86400
+    os.utime(path, (t, t))
+    return path
+
+
+@pytest.fixture
+def layout(db_sync, tmp_path):
+    db_sync.add(Artist(name="Libscan Maewix", slug="libscan-maewix"))
+    db_sync.commit()
+    post = tmp_path / "Libscan-Maewix" / "patreon" / "2026-05-01_123_Pack"
+    files = {
+        "missing": _write(post / "01_art.jpg", _jpeg(1)),
+        "owned": _write(post / "02_owned.jpg", _jpeg(2)),
+        "sidecar": _write(post / "01_art.json", b'{"category": "patreon", "id": "123"}'),
+        "staging": _write(post / "03_big.zip.part", b"partial"),
+        "recent": _write(post / "04_new.jpg", _jpeg(4), age_days=0),
+        "not_media": _write(post / "05_game.exe", b"MZ"),
+        "no_artist": _write(tmp_path / "libscan-nobody" / "x" / "a.jpg", _jpeg(5)),
+        "store": _write(tmp_path / "thumbs" / "abc" / "f.jpg", _jpeg(6)),
+    }
+    db_sync.add(ImageRecord(
+        path=str(files["owned"]), sha256="libscan-owned".ljust(64, "x"),
+        size_bytes=files["owned"].stat().st_size, mime="image/jpeg",
+        width=256, height=256, origin="downloaded", integrity_status="ok",
+    ))
+    db_sync.commit()
+    return tmp_path, files
+
+
+def test_finds_only_unrecorded_media_in_an_artists_folder(db_sync, layout):
+    """A differently-cased folder still matches its artist. Recorded files,
+    sidecars, staging files, the library's own stores, folders that match no
+    artist, files changed in the last day and non-media are not listed."""
+    root, files = layout
+    found, summary = library_scan.find_unimported(db_sync, root)
+
+    assert [u.path for u in found] == [files["missing"]]
+    assert found[0].artist_slug == "libscan-maewix"
+    assert found[0].task_type == "media"
+    assert summary["files"] == 1
+    assert summary["recent"] == 1
+    assert summary["not_media"] == 1
+    assert summary["no_artist"] == 1
+    assert summary["artists"][0]["slug"] == "libscan-maewix"
+    assert summary["artists"][0]["samples"] == [
+        "Libscan-Maewix/patreon/2026-05-01_123_Pack/01_art.jpg",
+    ]
+
+
+def test_queue_makes_a_library_batch_of_what_find_lists(db_sync, layout, monkeypatch):
+    """The import queued is exactly the previewed list."""
+    root, files = layout
+    queued = []
+    monkeypatch.setattr(import_file, "enqueue_import", lambda tid, tt: queued.append((tid, tt)))
+
+    summary = library_scan.queue_unimported(db_sync, root)
+
+    tasks = db_sync.execute(
+        select(ImportTask).where(ImportTask.batch_id == summary["batch_id"])
+    ).scalars().all()
+    assert [t.source_path for t in tasks] == [str(files["missing"])]
+    assert tasks[0].batch.scan_mode == "library"
+    assert queued == [(tasks[0].id, "media")]
+
+
+def test_a_library_import_attaches_in_place_and_removes_a_copy(db_sync, layout, monkeypatch):
+    """The file stays where it is and becomes the record's file. A byte-identical
+    copy found later is removed from disk, since the library already holds it."""
+    root, files = layout
+    monkeypatch.setattr(import_file, "IMAGES_ROOT", root)
+    importer = Importer(
+        session=db_sync, images_root=root, import_root=root,
+        thumbnailer=Thumbnailer(images_root=root),
+        settings=ImportSettings.load_sync(db_sync),
+    )
+
+    result = import_file._attach_where_it_lies(db_sync, importer, files["missing"])
+
+    assert result.status == "imported"
+    record = db_sync.get(ImageRecord, result.image_id)
+    assert record.path == str(files["missing"])
+    assert files["missing"].exists()
+    assert db_sync.get(Artist, record.artist_id).slug == "libscan-maewix"
+
+    copy = _write(files["missing"].parent / "09_copy.jpg", files["missing"].read_bytes())
+    again = import_file._attach_where_it_lies(db_sync, importer, copy)
+    assert again.status == "skipped"
+    assert not copy.exists()
+    assert files["missing"].exists()