Add grader field to GraphQL Submission Type

app/graphql/interfaces/submission_interface.rb

@@ -767,4 +767,9 @@ def version_query_param(submission)
       submission.attempt
     end
   end
+
+  field :grader, Types::UserType, null: true
+  def graded_by
+    load_association(:grader)
+  end
 end

schema.graphql

@@ -10658,6 +10658,7 @@ type Submission implements LegacyIDInterface & Node & SubmissionInterface & Time
   gradeMatchesCurrentSubmission: Boolean
   gradedAnonymously: Boolean
   gradedAt: DateTime
+  grader: User
   gradingPeriodId: ID
   gradingStatus: SubmissionGradingStatus
   groupId: ID

spec/graphql/types/submission_type_spec.rb

@@ -2827,4 +2827,20 @@
       expect(type.resolve("aiGradeResult { attempt }")).to be_nil
     end
   end
+
+  describe "grader" do
+    it "returns user for graded submission" do
+      expect(submission_type.resolve("grader { _id }")).to eq @teacher.id.to_s
+    end
+
+    it "returns nil for ungraded submissions" do
+      @submission.update!(grader_id: nil)
+      expect(submission_type.resolve("grader { _id }")).to be_nil
+    end
+
+    it "returns nil for automarked submissions" do
+      @submission.update!(grader_id: -1)
+      expect(submission_type.resolve("grader { _id }")).to be_nil
+    end
+  end
 end