Improve macro dispatch handling

Author: vchan

sqlmesh/dbt/adapter.py

@@ -139,11 +139,18 @@ def _relevance(package_name_pair: t.Tuple[t.Optional[str], str]) -> t.Tuple[int,
             return name_score, package_score
 
         jinja_env = self.jinja_macros.build_environment(**self.jinja_globals).globals
-        packages_to_check: t.Set[t.Optional[str]] = {
-            macro_namespace,
-            # self.jinja_macros.root_package_name,
-            *(k for k in jinja_env if k.startswith("dbt")),
-        }
+
+        # Build the set of packages to check based on dispatch configuration
+        packages_to_check: t.List[t.Optional[str]]
+        if macro_namespace is None:
+            packages_to_check = [None]
+        else:
+            if not packages_to_check and macro_namespace in jinja_env:
+                packages_to_check = [self.jinja_macros.root_package_name, macro_namespace]
+
+        # Add dbt packages as fallback
+        packages_to_check.extend(k for k in jinja_env if k.startswith("dbt"))
+
         candidates = {}
         for macro_package in packages_to_check:
             macros = jinja_env.get(macro_package, {}) if macro_package else jinja_env