feat: suggest confirmed external aliases

apps/api/app/community_review.py

@@ -34,6 +34,20 @@ def map_observation(
     return observation
 
 
+def suggest_aliases(session: Session, observation: ExternalObservation) -> tuple[Fish | None, Waterbody | None]:
+    fish_alias = session.scalar(select(ExternalEntityAlias).where(
+        ExternalEntityAlias.source_system == observation.source_system,
+        ExternalEntityAlias.entity_type == "fish",
+        ExternalEntityAlias.external_id == (observation.fish_external_id or observation.fish_name),
+    ))
+    waterbody_alias = session.scalar(select(ExternalEntityAlias).where(
+        ExternalEntityAlias.source_system == observation.source_system,
+        ExternalEntityAlias.entity_type == "waterbody",
+        ExternalEntityAlias.external_id == (observation.waterbody_external_id or observation.waterbody_name),
+    ))
+    return (fish_alias.fish if fish_alias else None, waterbody_alias.waterbody if waterbody_alias else None)
+
+
 def reject_observation(session: Session, observation: ExternalObservation, *, reason: str) -> ExternalObservation:
     if observation.status == "published":
         raise ExternalReviewError("published observation cannot be rejected")
@@ -109,6 +123,8 @@ def _save_alias(
             external_id=external_id, external_name=observation.fish_name if fish else observation.waterbody_name,
         )
         session.add(alias)
+    elif (fish is not None and alias.fish_id != fish.id) or (waterbody is not None and alias.waterbody_id != waterbody.id):
+        raise ExternalReviewError(f"confirmed {entity_type} alias points to another entity")
     alias.fish = fish
     alias.waterbody = waterbody
     alias.updated_at = datetime.now(timezone.utc)