feat(server): allow casting var assns

docs/docs/08-api.md

@@ -777,6 +777,7 @@ have to worry about this in daily LittleHorse usage.
 | `format_string` | oneof `source`| [VariableAssignment.FormatString](#variableassignmentformatstring) | Assign a format string |
 | `node_output` | oneof `source`| [VariableAssignment.NodeOutputReference](#variableassignmentnodeoutputreference) | Assign the value of a NodeOutput. |
 | `expression` | oneof `source`| [VariableAssignment.Expression](#variableassignmentexpression) | Assign the value of an Expression. |
+| `type_to_cast_to` | optional| [VariableType](#variabletype) | Allows casting this Variable Assignment to a specific type |
  <!-- end Fields -->
  <!-- end HasFields -->
 
@@ -792,6 +793,7 @@ An Expression allows you to combine multiple values into one.
 | `lhs` | | [VariableAssignment](#variableassignment) | The left-hand-side of the expression. |
 | `operation` | | [VariableMutationType](#variablemutationtype) | The operator in the expression. |
 | `rhs` | | [VariableAssignment](#variableassignment) | The right-hand-side of the expression. |
+| `type_to_cast_to` | optional| [VariableType](#variabletype) | Allows casting this expression to a specific type |
  <!-- end Fields -->
  <!-- end HasFields -->
 

schemas/littlehorse/common_wfspec.proto

@@ -47,6 +47,8 @@ message VariableAssignment {
     VariableMutationType operation = 2;
     // The right-hand-side of the expression.
     VariableAssignment rhs = 3;
+    // Allows casting this expression to a specific type
+    optional VariableType type_to_cast_to = 4;
   }
 
   // If you provide a `variable_name` and the specified variable is JSON_OBJ or
@@ -67,6 +69,8 @@ message VariableAssignment {
     // Assign the value of an Expression.
     Expression expression = 6;
   }
+  // Allows casting this Variable Assignment to a specific type
+  optional VariableType type_to_cast_to = 7;
 }
 
 // Enumerates the available operations to mutate a variable in a WfRun.