fixed relationship resolution in merger and queryer

src/database/schema.rs

@@ -622,7 +622,23 @@ pub(crate) fn resolve_relation<'a>(
     }
   }
 
+  if !resolved {
+    // 1. If there's EXACTLY ONE relation with a null prefix, it's the base structural edge. Pick it.
+    let mut null_prefix_ids = Vec::new();
+    for (i, rel) in matching_rels.iter().enumerate() {
+      if rel.prefix.is_none() {
+        null_prefix_ids.push(i);
+      }
+    }
+    if null_prefix_ids.len() == 1 {
+      chosen_idx = null_prefix_ids[0];
+      resolved = true;
+    }
+  }
+
   if !resolved && relative_keys.is_some() {
+    // 2. M:M Disambiguation: The child schema will explicitly define an outbound property
+    // matching one of the relational prefixes (e.g. "target"). We use the OTHER one (e.g. "source").
     let keys = relative_keys.unwrap();
     let mut missing_prefix_ids = Vec::new();
     for (i, rel) in matching_rels.iter().enumerate() {
@@ -634,6 +650,7 @@ pub(crate) fn resolve_relation<'a>(
     }
     if missing_prefix_ids.len() == 1 {
       chosen_idx = missing_prefix_ids[0];
+      // resolved = true;
     }
   }