Closes #14

changelog.md

@@ -10,6 +10,13 @@ existing Git tag; subsequent changes are listed as unreleased.
 
 #### Added
 
+- Stable application identifiers: `FrameKey` (normalized CAN ID and frame type)
+  and `SignalKey` (frame key and signal name), with equality and hashers.
+- Runtime `FindSignal`, frame `GetKey`, and keys on decoded frame/signal results.
+- Reload/lifetime tests for retained frames and independent signals, lookup
+  handles, copies/moves, snapshot release, stable keys, removed/renamed definitions,
+  failed/empty reloads, duplicate keys, and insufficient payloads.
+
 - `ParseFileWithDiagnostics` and `DbcParseResult` with severity, stable error
   code, supplied file path, physical line number, and message for each diagnostic.
 - Warnings for unregistered statements, including floating-point signal types,
@@ -21,6 +28,16 @@ existing Git tag; subsequent changes are listed as unreleased.
 
 #### Changed
 
+- **API change:** `DecodeDatabase` is an immutable shared snapshot. Use
+  `GetFrames()` for reads or construct a new snapshot from a vector; its frame
+  index is private and built automatically, with duplicate-key validation.
+- **API change:** decoded `definition` fields and `DbcDecoder::FindFrame` return
+  `shared_ptr<const ...>` ownership. Stored results retain old definitions across
+  reload/clear/destruction, including separately copied signals and `VAL_` strings.
+  Decoding shares metadata without per-result definition copies.
+- Documented borrowed views, owning handles, snapshot retention, identifier scope,
+  reload behavior, application migration, and synchronization requirements.
+
 - Kept `ParseFile` compatible while sharing parsing with the diagnostic API.
   Parsing stops at the first error and never returns a partial database.
 - Deferred value-description and multiplexing errors carry structured source