fix(simple-executor): return consistent column names using dot notation (#84)

* fix(simple-executor): return consistent column names using dot notation

Update simple executor to return Cypher dot notation (e.g., p.name)
instead of double underscore format (e.g., p__name) for column names.
This ensures consistency with the DataFusion executor output.

Changes:
- Add to_cypher_column_name() function to convert to dot notation
- Update apply_return_with_qualifier() to apply conversion for final output
- Add unit tests for the new function
- Preserve explicit user-provided aliases

Fixes #30

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

* cargo fmt

---------

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: ex172000

rust/lance-graph/src/simple_executor/aliases.rs

@@ -1,6 +1,33 @@
 // SPDX-License-Identifier: Apache-2.0
 // SPDX-FileCopyrightText: Copyright The Lance Authors
 
+/// Qualify a column name for internal DataFusion operations.
+/// Returns format: `alias__property` (e.g., "p__name").
+/// Note: This is for internal use only. Final output uses Cypher dot notation.
 pub(super) fn qualify_alias_property(alias: &str, property: &str) -> String {
     format!("{}__{}", alias, property)
 }
+
+/// Convert to Cypher-style column name for query results.
+/// Returns format: `alias.property` (e.g., "p.name").
+/// This matches the output format used by the DataFusion executor.
+pub(super) fn to_cypher_column_name(alias: &str, property: &str) -> String {
+    format!("{}.{}", alias, property)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_qualify_alias_property() {
+        assert_eq!(qualify_alias_property("p", "name"), "p__name");
+        assert_eq!(qualify_alias_property("person", "age"), "person__age");
+    }
+
+    #[test]
+    fn test_to_cypher_column_name() {
+        assert_eq!(to_cypher_column_name("p", "name"), "p.name");
+        assert_eq!(to_cypher_column_name("c", "company_name"), "c.company_name");
+    }
+}

rust/lance-graph/src/simple_executor/clauses.rs

@@ -37,6 +37,10 @@ pub(super) fn apply_return_with_qualifier(
             let mut e = datafusion::logical_expr::col(col_name);
             if let Some(a) = &item.alias {
                 e = e.alias(a);
+            } else {
+                let cypher_name =
+                    super::aliases::to_cypher_column_name(&prop.variable, &prop.property);
+                e = e.alias(cypher_name);
             }
             proj.push(e);
         }