Closes #16

changelog.md

@@ -6,6 +6,20 @@ existing Git tag; subsequent changes are listed as unreleased.
 
 ## Unreleased
 
+### 2026-10-14
+
+#### Changed
+
+- Validate duplicate frame keys before building the runtime lookup index, alongside
+  CAN IDs, signal layouts, numeric parameters, and multiplexing metadata.
+
+#### Added
+
+- Exhaustive layout checks for both byte orders at representative payload sizes
+  (0, 1, 8, 64, and 255 bytes), including invalid lengths and uint32 overflow inputs.
+- Regression coverage for builder input mutation/destruction and failed replacement
+  with duplicate frame or signal keys, preserving existing lookups.
+
 ### 2026-10-13
 
 #### Added