ad-hoc journal_id needs fix now

common/proto/accounting.proto

@@ -26,9 +26,9 @@ service Accounting {
   rpc SoftDeleteJournalLine(SoftDeleteJournalLineRequest) returns (Journal);
 }
 
-// Tables with an active posting script accept journal_id as a reserved key in
-// PostTableDataRequest.data. It selects the journal receiving generated lines
-// and is removed before the source row is validated or stored.
+// Tables with an active posting script define journal_id as a permanent BIGINT
+// column. PostTableDataRequest.data must include it; the value is stored on the
+// source row and selects the journal receiving generated lines.
 
 enum JournalSide {
   JOURNAL_SIDE_UNSPECIFIED = 0;