Closes #17

changelog.md

@@ -15,6 +15,13 @@ existing Git tag; subsequent changes are listed as unreleased.
 
 #### Added
 
+- Root `AGENTS.md` with project coding rules, build/test commands, and
+  documentation requirements, based on the existing `.project_rules`.
+- End-to-end DBC fixture tests for parsed metadata, runtime frame/signal lookup,
+  raw and physical decoding, value descriptions, and tree nodes. Both builders
+  preserve supported metadata across same-numeric standard/extended IDs, comments,
+  empty databases, and database replacement.
+
 - 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