account is always FK from now on

common/proto/table_definition.proto

@@ -55,6 +55,10 @@ message TableLink {
   // Otherwise the column allows NULL.
   // Duplicate links to the same target table in one request are rejected.
   bool required = 2;
+
+  // User-defined column read from this linked row as the journal account.
+  // Exactly one required link must set this when the table contains ACCOUNTING.
+  string account_value_column = 3;
 }
 
 // Defines the input for creating a new table definition.