introduce recipe_exception in result.proto

recipe_engine/result.proto

 syntax = "proto3";
 
 package recipe_engine;
 
 import "package.proto";
 
 // The result of a recipe execution.
 message Result {
   oneof oneof_result {
     // The json result of a recipe. Guaranteed to be a JSON 'object' (e.g.
@@ skipping 10 matching lines @@
 
 message Failure {
   // A reason readable by humans. Printed to the UI, and will be seen by users.
   string human_reason = 1;
 
   // The cause of this failure.
   oneof failure_type {
     // Step timed out.
     Timeout timeout = 2;
 
-    // Step threw an exception.
+    // Recipe engine threw an exception.
     Exception exception = 3;
 
+    // A recipe threw an exception.
+    RecipeException recipe_exception = 6;
+
     // Step accessed invalid step data.
     StepData step_data = 4;
 
     // Step failed (return code not ok).
     StepFailure failure = 5;
   }
 }
 
-// An unexpected exception occured during execution. Caused by the builtin
-// Exception class.
+// Recipe engine raised an unexpected exception during execution.
+// Caused by the builtin Exception class.
 message Exception {
   // Traceback of an exception which occured.
   repeated string traceback = 1;
 }
 
+// A recipe raised an unexpected exception during execution.
+// Caused by the builtin Exception class.
+message RecipeException {
+  // Traceback of an exception which occured.
+  repeated string traceback = 1;
+}
+
 // A step timed out during its execution. Caused by StepTimeout in
 // recipe_api.py
 message Timeout {
   // The timeout set for the step.
   float timeout_s = 1;
 }
 
 // A step attempted to access data which did not exist. Caused by
 // StepDataAttributeError in types.py.
 message StepData {
   // The step which attempted to access invalid data.
   string step = 1;
 }
 
 // A step failed to execute "correctly". Correct generally is indicated by a
 // return code of 0, but the step can allow for other return codes as well.
 message StepFailure {
   // The step which failed.
   string step = 1;
 }