Enforce exactly one value key per field in set_issue_fields (#2339)

* Initial plan

* Enforce exactly one value key per field in set_issue_fields and add tests

Address review feedback:
- Change validation to count value keys and reject when multiple are
  provided (e.g., text_value + number_value, or text_value + delete).
- Add unit tests for multiple value keys and value + delete scenarios.
- Run generate-docs (no doc changes needed; README was already current).

Agent-Logs-Url: https://github.com/github/github-mcp-server/sessions/7e89edb3-5315-42dd-bfa1-6c962f1ba137

Co-authored-by: mattdholloway <918573+mattdholloway@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: mattdholloway <918573+mattdholloway@users.noreply.github.com>

Author: 2 people

pkg/github/granular_tools_test.go

@@ -907,4 +907,42 @@ func TestGranularSetIssueFields(t *testing.T) {
 		textContent := getTextResult(t, result)
 		assert.Contains(t, textContent.Text, "each field must have a value")
 	})
+
+	t.Run("multiple value keys returns error", func(t *testing.T) {
+		deps := BaseDeps{}
+		serverTool := GranularSetIssueFields(translations.NullTranslationHelper)
+		handler := serverTool.Handler(deps)
+
+		request := createMCPRequest(map[string]any{
+			"owner":        "owner",
+			"repo":         "repo",
+			"issue_number": float64(5),
+			"fields": []any{
+				map[string]any{"field_id": "FIELD_1", "text_value": "hello", "number_value": float64(42)},
+			},
+		})
+		result, err := handler(ContextWithDeps(context.Background(), deps), &request)
+		require.NoError(t, err)
+		textContent := getTextResult(t, result)
+		assert.Contains(t, textContent.Text, "each field must have exactly one value")
+	})
+
+	t.Run("value key with delete returns error", func(t *testing.T) {
+		deps := BaseDeps{}
+		serverTool := GranularSetIssueFields(translations.NullTranslationHelper)
+		handler := serverTool.Handler(deps)
+
+		request := createMCPRequest(map[string]any{
+			"owner":        "owner",
+			"repo":         "repo",
+			"issue_number": float64(5),
+			"fields": []any{
+				map[string]any{"field_id": "FIELD_1", "text_value": "hello", "delete": true},
+			},
+		})
+		result, err := handler(ContextWithDeps(context.Background(), deps), &request)
+		require.NoError(t, err)
+		textContent := getTextResult(t, result)
+		assert.Contains(t, textContent.Text, "each field must have exactly one value")
+	})
 }

pkg/github/issues_granular.go

@@ -731,41 +731,44 @@ func GranularSetIssueFields(t translations.TranslationHelperFunc) inventory.Serv
 					FieldID: githubv4.ID(fieldID),
 				}
 
-				// Check for exactly one value type (or delete)
-				hasValue := false
+				// Count how many value keys are present; exactly one is required.
+				valueCount := 0
 
 				if v, err := OptionalParam[string](fieldMap, "text_value"); err == nil && v != "" {
 					input.TextValue = githubv4.NewString(githubv4.String(v))
-					hasValue = true
+					valueCount++
 				}
 				if v, err := OptionalParam[float64](fieldMap, "number_value"); err == nil {
 					if _, exists := fieldMap["number_value"]; exists {
 						gqlFloat := githubv4.Float(v)
 						input.NumberValue = &gqlFloat
-						hasValue = true
+						valueCount++
 					}
 				}
 				if v, err := OptionalParam[string](fieldMap, "date_value"); err == nil && v != "" {
 					input.DateValue = githubv4.NewString(githubv4.String(v))
-					hasValue = true
+					valueCount++
 				}
 				if v, err := OptionalParam[string](fieldMap, "single_select_option_id"); err == nil && v != "" {
 					optionID := githubv4.ID(v)
 					input.SingleSelectOptionID = &optionID
-					hasValue = true
+					valueCount++
 				}
 				if _, exists := fieldMap["delete"]; exists {
 					del, err := OptionalParam[bool](fieldMap, "delete")
 					if err == nil && del {
 						deleteVal := githubv4.Boolean(true)
 						input.Delete = &deleteVal
-						hasValue = true
+						valueCount++
 					}
 				}
 
-				if !hasValue {
+				if valueCount == 0 {
 					return utils.NewToolResultError("each field must have a value (text_value, number_value, date_value, single_select_option_id) or delete: true"), nil, nil
 				}
+				if valueCount > 1 {
+					return utils.NewToolResultError("each field must have exactly one value (text_value, number_value, date_value, single_select_option_id) or delete: true, but multiple were provided"), nil, nil
+				}
 
 				issueFields = append(issueFields, input)
 			}