Closes #12

changelog.md

@@ -24,6 +24,14 @@ existing Git tag; subsequent changes are listed as unreleased.
 
 - Overlapping unconditional signals are now rejected during parsing.
 
+#### Fixed
+
+- Reject duplicate frames by normalized CAN ID and frame type, including
+  equivalent extended ID encodings, and duplicate signal names within a frame.
+  Errors report the file path and line of the repeated definition. Standard and
+  extended frames may share a numeric ID; separate frames may reuse signal names.
+  Added regression coverage and updated parser documentation.
+
 ### 2026-10-06
 
 #### Added