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

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

backend/app/services/tag_service.py

@@ -412,4 +412,47 @@ class TagService:
     async def _create_protective_aliases(
         self, src_name: str, src_kind: TagKind, tgt: int
     ) -> bool:
-        return False
+        """One alias per category the tagger has actually emitted for
+        src_name (so future predictions resolve to target); fall back to
+        the tag's kind when the tagger never predicted this exact name.
+        Idempotent — never clobbers a pre-existing operator alias."""
+        from ..models.tag_alias import TagAlias
+
+        rows = (
+            await self.session.execute(
+                text(
+                    "SELECT DISTINCT "
+                    "  (tagger_predictions::jsonb -> :n ->> 'category') "
+                    "  AS cat "
+                    "FROM image_record "
+                    "WHERE tagger_predictions IS NOT NULL "
+                    "  AND (tagger_predictions::jsonb) ? :n"
+                ),
+                {"n": src_name},
+            )
+        ).all()
+        categories = {r.cat for r in rows if r.cat}
+        if not categories:
+            kind_val = (
+                src_kind.value
+                if hasattr(src_kind, "value")
+                else str(src_kind)
+            )
+            categories = {kind_val}
+
+        created = False
+        for cat in categories:
+            res = await self.session.execute(
+                pg_insert(TagAlias)
+                .values(
+                    alias_string=src_name,
+                    alias_category=cat,
+                    canonical_tag_id=tgt,
+                )
+                .on_conflict_do_nothing(
+                    index_elements=["alias_string", "alias_category"]
+                )
+            )
+            if res.rowcount:
+                created = True
+        return created