Index: scripts/MsgUtils/msgutils/templates/MsgDefs_proto.jinja
===================================================================
diff -u -re3aaafd456d2a3b791400e90fbc380372da56ff9 -r53d80d0edc1c441132b13f387f5f13570a7aafd2
--- scripts/MsgUtils/msgutils/templates/MsgDefs_proto.jinja	(.../MsgDefs_proto.jinja)	(revision e3aaafd456d2a3b791400e90fbc380372da56ff9)
+++ scripts/MsgUtils/msgutils/templates/MsgDefs_proto.jinja	(.../MsgDefs_proto.jinja)	(revision 53d80d0edc1c441132b13f387f5f13570a7aafd2)
@@ -7,12 +7,19 @@
 
 import "google/protobuf/timestamp.proto";
 
+// Header is required as the first field (i.e. 'Header header = 1;') of every message.
 message Header {
     string deviceSerialNum = 1;
     google.protobuf.Timestamp timestamp = 2;
     uint32 msgId = 3;
-    uint32 sequence = 4;
+    int32 sequence = 4;
 }
+
+// Envelope is a minimal wrapper used to extract the Header from serialized messages without knowing the
+// concrete message type at parse time. Every message requires Header at field 1.
+message Envelope {
+    Header header = 1;
+}
 {%- for (msg_id, msg) in msg_proto.data.items() %}
 
 // {{ msg['msg_id'] }} ({{ msg['msg_id_hex_string'] }})