feat(tags): protective alias creation per observed tagger category with kind fallback

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

tests/test_tag_merge.py

@@ -302,3 +302,103 @@ async def test_merge_fandom_reparents_children(db):
     db.expire_all()  # merge() uses Core DML; drop stale identity-map state
     refreshed = await db.get(Tag, child.id)
     assert refreshed.fandom_id == f_tgt.id
+
+
+@pytest.mark.asyncio
+async def test_no_alias_when_purely_manual(db):
+    from backend.app.models.tag_alias import TagAlias
+
+    svc = TagService(db)
+    a = await svc.find_or_create("ManualOnly", TagKind.general)
+    b = await svc.find_or_create("CanonM", TagKind.general)
+    img = await _img(db)
+    await svc.add_to_image(img, a.id, source="manual")
+    result = await svc.merge(a.id, b.id)
+    assert result.alias_created is False
+    assert (await db.execute(select(TagAlias))).first() is None
+
+
+@pytest.mark.asyncio
+async def test_alias_per_observed_prediction_category(db):
+    from backend.app.models import ImageRecord
+    from backend.app.models.tag_alias import TagAlias
+
+    svc = TagService(db)
+    a = await svc.find_or_create("predname", TagKind.general)
+    b = await svc.find_or_create("CanonP", TagKind.general)
+    img = await _img(db)
+    # mark source machine-known so keep_as_alias is True
+    await svc.add_to_image(img, a.id, source="ml_auto")
+    r1 = await db.get(ImageRecord, img)
+    r1.tagger_predictions = {
+        "predname": {"category": "general", "confidence": 0.9}
+    }
+    i2 = await _img(db)
+    r2 = await db.get(ImageRecord, i2)
+    r2.tagger_predictions = {
+        "predname": {"category": "copyright", "confidence": 0.8}
+    }
+    await db.flush()
+    result = await svc.merge(a.id, b.id)
+    assert result.alias_created is True
+    db.expire_all()
+    rows = (await db.execute(select(TagAlias))).scalars().all()
+    assert {(r.alias_string, r.alias_category) for r in rows} == {
+        ("predname", "general"),
+        ("predname", "copyright"),
+    }
+    assert all(r.canonical_tag_id == b.id for r in rows)
+
+
+@pytest.mark.asyncio
+async def test_alias_fallback_to_kind_when_no_predictions(db):
+    from backend.app.models.tag_alias import TagAlias
+
+    svc = TagService(db)
+    a = await svc.find_or_create("AllowNoPred", TagKind.character)
+    b = await svc.find_or_create("CanonF", TagKind.character)
+    db.add(TagAllowlist(tag_id=a.id))
+    await db.flush()
+    result = await svc.merge(a.id, b.id)
+    assert result.alias_created is True
+    db.expire_all()
+    al = (
+        await db.execute(
+            select(TagAlias).where(TagAlias.alias_string == "AllowNoPred")
+        )
+    ).scalar_one()
+    assert al.alias_category == "character"
+    assert al.canonical_tag_id == b.id
+
+
+@pytest.mark.asyncio
+async def test_alias_create_does_not_clobber_existing(db):
+    from backend.app.models import ImageRecord
+    from backend.app.models.tag_alias import TagAlias
+
+    svc = TagService(db)
+    a = await svc.find_or_create("dupalias", TagKind.general)
+    b = await svc.find_or_create("CanonD", TagKind.general)
+    other = await svc.find_or_create("OtherCanon", TagKind.general)
+    db.add(
+        TagAlias(
+            alias_string="dupalias",
+            alias_category="general",
+            canonical_tag_id=other.id,
+        )
+    )
+    img = await _img(db)
+    await svc.add_to_image(img, a.id, source="ml_auto")
+    r = await db.get(ImageRecord, img)
+    r.tagger_predictions = {
+        "dupalias": {"category": "general", "confidence": 0.9}
+    }
+    await db.flush()
+    await svc.merge(a.id, b.id)
+    db.expire_all()
+    al = (
+        await db.execute(
+            select(TagAlias).where(TagAlias.alias_string == "dupalias")
+        )
+    ).scalar_one()
+    assert al.canonical_tag_id == other.id  # pre-existing alias untouched