Closes #24

changelog.md

@@ -8,6 +8,21 @@ existing Git tag; subsequent changes are listed as unreleased.
 
 ### 2026-10-20
 
+#### Changed
+
+- J1939 interpretation now requires `DbcParserOptions::enableJ1939` (default off)
+  or explicit per-frame `hasPgn` metadata. Extended CAN alone no longer derives
+  PGN metadata. Runtime construction validates opted-in PGNs against frame IDs.
+- Add indexed PGN lookup with PDU1 destination exclusion, PDU2 group extension,
+  and both data-page bits. Decoder exact-ID matches take precedence; otherwise
+  one J1939 PGN candidate is accepted and multiple candidates return
+  `AmbiguousFrame`. Result and selection keys identify the DBC definition.
+- Add opt-in, PDU1/PDU2, address/priority changes, ambiguity, exact precedence,
+  metadata validation, selected decode, and snapshot-lifetime regressions.
+  Verified with `qmake6 ../dbc.pro`, `make -j4`, and `make check` in `build/`:
+  all six QtTest suites and the Qt-free tree target passed; the existing named
+  comma-decimal C locale test skipped because that locale is not installed.
+
 #### Added
 
 - Expose stable frame and signal keys from Qt-free tree nodes using the existing