Sort lines with identical vertical position by horizontal position in…

… DataExtractor

src/stratigraphy/data_extractor/data_extractor.py

@@ -195,8 +195,12 @@ def get_lines_near_key(self, lines, key_line: TextLine) -> list[TextLine]:
         feature_lines.insert(0, key_line)
         feature_lines = list(dict.fromkeys(feature_lines))
 
-        # Sort by vertical distance between the top of the feature line and the top of key_line
-        feature_lines_sorted = sorted(feature_lines, key=lambda line: abs(line.rect.y0 - key_line.rect.y0))
+        # Sort by
+        # - vertical distance between the top of the feature line and the top of key_line
+        # - horizontal position (left-first) for lines with identical vertical position
+        feature_lines_sorted = sorted(
+            feature_lines, key=lambda line: (abs(line.rect.y0 - key_line.rect.y0), line.rect.x0)
+        )
 
         return feature_lines_sorted