fix(fc2a): satisfy ruff 0.15.13 lint — UP017, UP042, I001

Ruff lint surfaced 23 violations across three rules; all addressed:

UP017 (Use datetime.UTC alias):
  Replaced 13 sites of datetime.now(timezone.utc) with datetime.now(UTC),
  also adjusted from-imports accordingly. UTC is a Python 3.11+ alias for
  timezone.utc that ruff's pyupgrade rules prefer.

UP042 (StrEnum):
  Replaced `class TagKind(str, Enum)` and `class SkipReason(str, Enum)`
  with `class Foo(StrEnum)`. StrEnum was added in Python 3.11 stdlib and
  is the modern idiom. Behavior is equivalent for our usage (the .value
  attribute, str(member) semantics).

I001 (Import sorting):
  Added `known-first-party = ["backend"]` to ruff.toml's [lint.isort] so
  ruff groups `backend.*` imports correctly. Without it, ruff treated
  them as third-party and demanded a different grouping. The existing
  import order is stdlib → third-party → first-party → local relative,
  which ruff now accepts.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/api/import_admin.py

@@ -1,6 +1,6 @@
 """Import admin API: trigger scan, list tasks, retry, clear."""
 
-from datetime import datetime, timedelta, timezone
+from datetime import UTC, datetime, timedelta
 
 from quart import Blueprint, jsonify, request
 from sqlalchemy import delete, select, update
@@ -137,7 +137,7 @@ async def clear_completed():
         return jsonify({"error": "status must be a list"}), 400
 
     cutoff = (
-        datetime.now(timezone.utc) - timedelta(days=int(age_days)) if age_days else None
+        datetime.now(UTC) - timedelta(days=int(age_days)) if age_days else None
     )
 
     Session = _session_factory()

backend/app/models/tag.py

@@ -7,7 +7,7 @@ different kinds and the same character name can exist in different fandoms.
 """
 
 from datetime import datetime
-from enum import Enum
+from enum import StrEnum
 
 from sqlalchemy import (
     CheckConstraint,
@@ -25,7 +25,7 @@ from sqlalchemy.orm import Mapped, mapped_column, relationship
 from .base import Base
 
 
-class TagKind(str, Enum):
+class TagKind(StrEnum):
     artist = "artist"
     character = "character"
     fandom = "fandom"

backend/app/services/importer.py

@@ -11,7 +11,7 @@ by the task. The Quart side uses an async session via the same models.
 import hashlib
 import shutil
 from dataclasses import dataclass
-from enum import Enum
+from enum import StrEnum
 from pathlib import Path
 
 from PIL import Image
@@ -25,7 +25,7 @@ from ..utils.slug import slugify
 from .thumbnailer import Thumbnailer
 
 
-class SkipReason(str, Enum):
+class SkipReason(StrEnum):
     too_small = "too_small"
     too_transparent = "too_transparent"
     single_color = "single_color"

backend/app/tasks/import_file.py

@@ -2,7 +2,7 @@
 updates the ImportTask state machine + ImportBatch counters atomically.
 """
 
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 from pathlib import Path
 
 from sqlalchemy import create_engine, select, update
@@ -34,7 +34,7 @@ def import_media_file(self, import_task_id: int) -> dict:
             return {"status": "missing", "task_id": import_task_id}
 
         task.status = "processing"
-        task.started_at = datetime.now(timezone.utc)
+        task.started_at = datetime.now(UTC)
         session.add(task)
         session.commit()
 
@@ -55,7 +55,7 @@ def import_media_file(self, import_task_id: int) -> dict:
         except Exception as exc:  # pragma: no cover — pipeline crash
             task.status = "failed"
             task.error = f"{type(exc).__name__}: {exc}"
-            task.finished_at = datetime.now(timezone.utc)
+            task.finished_at = datetime.now(UTC)
             session.execute(
                 update(ImportBatch)
                 .where(ImportBatch.id == task.batch_id)
@@ -86,7 +86,7 @@ def import_media_file(self, import_task_id: int) -> dict:
             counter_col_name = "failed"
             counter_col = ImportBatch.failed
 
-        task.finished_at = datetime.now(timezone.utc)
+        task.finished_at = datetime.now(UTC)
         session.execute(
             update(ImportBatch)
             .where(ImportBatch.id == task.batch_id)
@@ -114,7 +114,7 @@ def import_media_file(self, import_task_id: int) -> dict:
                 .where(ImportBatch.id == task.batch_id)
                 .values(
                     status="complete",
-                    finished_at=datetime.now(timezone.utc),
+                    finished_at=datetime.now(UTC),
                 )
             )
             session.commit()

backend/app/tasks/maintenance.py

@@ -1,6 +1,6 @@
 """Periodic maintenance: recover stuck import tasks, garbage-collect old finished tasks."""
 
-from datetime import datetime, timedelta, timezone
+from datetime import UTC, datetime, timedelta
 
 from sqlalchemy import create_engine, delete, select, update
 from sqlalchemy.orm import sessionmaker
@@ -29,7 +29,7 @@ def recover_interrupted_tasks() -> int:
     forever) without resetting slow-but-still-running jobs.
     """
     SessionLocal = _sync_session_factory()
-    cutoff = datetime.now(timezone.utc) - timedelta(minutes=STUCK_THRESHOLD_MINUTES)
+    cutoff = datetime.now(UTC) - timedelta(minutes=STUCK_THRESHOLD_MINUTES)
     with SessionLocal() as session:
         stuck_ids = session.execute(
             select(ImportTask.id)
@@ -63,7 +63,7 @@ def cleanup_old_tasks() -> int:
     rather than an archive. Matches IR's default.
     """
     SessionLocal = _sync_session_factory()
-    cutoff = datetime.now(timezone.utc) - timedelta(days=OLD_TASK_DAYS)
+    cutoff = datetime.now(UTC) - timedelta(days=OLD_TASK_DAYS)
     with SessionLocal() as session:
         result = session.execute(
             delete(ImportTask)

ruff.toml

@@ -19,5 +19,10 @@ ignore = [
 "alembic/versions/*.py" = ["E", "F", "I", "UP"]
 "tests/*" = ["F401"]
 
+[lint.isort]
+# Tell ruff that `backend` is our first-party module so imports get
+# grouped correctly: stdlib, third-party, first-party, then local relative.
+known-first-party = ["backend"]
+
 [format]
 quote-style = "double"

tests/test_api_gallery.py

@@ -1,4 +1,4 @@
-from datetime import datetime, timedelta, timezone
+from datetime import UTC, datetime, timedelta
 
 import pytest
 
@@ -18,7 +18,7 @@ async def client(app):
 
 
 async def _seed(db, count: int = 3):
-    base = datetime.now(timezone.utc)
+    base = datetime.now(UTC)
     for i in range(count):
         r = ImageRecord(
             path=f"/images/x/{i}.jpg",

tests/test_api_import_admin.py

@@ -1,4 +1,4 @@
-from datetime import datetime, timedelta, timezone
+from datetime import UTC, datetime, timedelta
 
 import pytest
 
@@ -46,7 +46,7 @@ async def test_list_tasks_with_status_filter(client, db):
     for status in ("complete", "failed", "complete"):
         db.add(ImportTask(
             batch_id=batch.id, source_path="/x", task_type="media", status=status,
-            finished_at=datetime.now(timezone.utc),
+            finished_at=datetime.now(UTC),
         ))
     await db.commit()
 
@@ -74,14 +74,14 @@ async def test_clear_completed(client, db):
     batch = ImportBatch(triggered_by="manual", source_path="/import", scan_mode="quick")
     db.add(batch)
     await db.flush()
-    long_ago = datetime.now(timezone.utc) - timedelta(days=30)
+    long_ago = datetime.now(UTC) - timedelta(days=30)
     db.add(ImportTask(
         batch_id=batch.id, source_path="/x", task_type="media",
         status="complete", finished_at=long_ago,
     ))
     db.add(ImportTask(
         batch_id=batch.id, source_path="/y", task_type="media",
-        status="complete", finished_at=datetime.now(timezone.utc),
+        status="complete", finished_at=datetime.now(UTC),
     ))
     await db.commit()
 

tests/test_gallery_service.py

@@ -1,4 +1,4 @@
-from datetime import datetime, timedelta, timezone
+from datetime import UTC, datetime, timedelta
 
 import pytest
 
@@ -12,7 +12,7 @@ from backend.app.services.gallery_service import (
 
 
 def _now():
-    return datetime.now(timezone.utc)
+    return datetime.now(UTC)
 
 
 async def _seed_images(db, count: int, sha_prefix: str = "0") -> list[ImageRecord]:
@@ -37,7 +37,7 @@ async def _seed_images(db, count: int, sha_prefix: str = "0") -> list[ImageRecor
 
 
 def test_cursor_roundtrip():
-    ts = datetime(2026, 5, 14, 12, 30, 0, tzinfo=timezone.utc)
+    ts = datetime(2026, 5, 14, 12, 30, 0, tzinfo=UTC)
     encoded = encode_cursor(ts, 42)
     back_ts, back_id = decode_cursor(encoded)
     assert back_ts == ts

tests/test_maintenance.py

@@ -2,7 +2,7 @@
 function runs synchronously inside the same DB transaction as the test.
 """
 
-from datetime import datetime, timedelta, timezone
+from datetime import UTC, datetime, timedelta
 
 import pytest
 
@@ -26,7 +26,7 @@ def _make_batch(session) -> int:
 
 def test_recover_interrupted_only_old(db_sync):
     batch_id = _make_batch(db_sync)
-    now = datetime.now(timezone.utc)
+    now = datetime.now(UTC)
 
     fresh = ImportTask(
         batch_id=batch_id, source_path="/import/a.jpg", task_type="media",
@@ -52,7 +52,7 @@ def test_recover_interrupted_only_old(db_sync):
 
 def test_cleanup_old_deletes_finished_old(db_sync):
     batch_id = _make_batch(db_sync)
-    now = datetime.now(timezone.utc)
+    now = datetime.now(UTC)
 
     old_complete = ImportTask(
         batch_id=batch_id, source_path="/import/a.jpg", task_type="media",