feat(tags): TagMergeConflict + provenance helper, enrich rename collision

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

tests/test_tag_merge.py

@@ -0,0 +1,78 @@
+import pytest
+
+from backend.app.models import Tag, TagKind, image_tag
+from backend.app.models.tag_allowlist import TagAllowlist
+from backend.app.services.tag_service import (
+    TagMergeConflict,
+    TagService,
+    TagValidationError,
+)
+
+pytestmark = pytest.mark.integration
+
+_IMG_SEQ = 0
+
+
+async def _img(db):
+    """Insert a minimal valid ImageRecord (all NOT NULL cols satisfied:
+    path, sha256, size_bytes, mime, origin) and return its id."""
+    global _IMG_SEQ
+    _IMG_SEQ += 1
+    from backend.app.models import ImageRecord
+
+    rec = ImageRecord(
+        path=f"/tmp/fc_merge_{_IMG_SEQ}.png",
+        sha256=f"{_IMG_SEQ:064d}",
+        size_bytes=1,
+        mime="image/png",
+        origin="uploaded",
+    )
+    db.add(rec)
+    await db.flush()
+    return rec.id
+
+
+@pytest.mark.asyncio
+async def test_rename_collision_raises_merge_conflict_with_payload(db):
+    svc = TagService(db)
+    target = await svc.find_or_create("Existing", TagKind.character)
+    source = await svc.find_or_create("Dupe", TagKind.character)
+    img = await _img(db)
+    await svc.add_to_image(img, source.id, source="manual")
+
+    with pytest.raises(TagMergeConflict) as ei:
+        await svc.rename(source.id, "Existing")
+    exc = ei.value
+    assert exc.target_id == target.id
+    assert exc.target_name == "Existing"
+    assert exc.source_image_count == 1
+    assert exc.will_alias is False  # purely manual, ML-unknown
+
+
+@pytest.mark.asyncio
+async def test_merge_conflict_is_a_tag_validation_error(db):
+    assert issubclass(TagMergeConflict, TagValidationError)
+
+
+@pytest.mark.asyncio
+async def test_will_alias_true_when_machine_sourced(db):
+    svc = TagService(db)
+    await svc.find_or_create("Canon", TagKind.general)
+    source = await svc.find_or_create("Auto", TagKind.general)
+    img = await _img(db)
+    await svc.add_to_image(img, source.id, source="ml_auto")
+    with pytest.raises(TagMergeConflict) as ei:
+        await svc.rename(source.id, "Canon")
+    assert ei.value.will_alias is True
+
+
+@pytest.mark.asyncio
+async def test_will_alias_true_when_allowlisted(db):
+    svc = TagService(db)
+    await svc.find_or_create("Canon2", TagKind.general)
+    source = await svc.find_or_create("Allowed", TagKind.general)
+    db.add(TagAllowlist(tag_id=source.id))
+    await db.flush()
+    with pytest.raises(TagMergeConflict) as ei:
+        await svc.rename(source.id, "Canon2")
+    assert ei.value.will_alias is True