fix(performance): restore project prop usage and error handling in transaction threshold modal

- Fix dropped project prop by updating useEventViewProject to accept optional project parameter
- Fix missing DELETE error handler in handleReset by adding .catch() block
- Ensures correct project is used in multi-project views
- Prevents unhandled promise rejections when reset fails

Author: cursoragent

static/app/views/performance/transactionSummary/projectUtils.ts

@@ -4,14 +4,22 @@ import type {Project} from 'sentry/types/project';
 import {defined} from 'sentry/utils';
 import type EventView from 'sentry/utils/discover/eventView';
 
-export function useEventViewProject(eventView: EventView, projects: Project[]) {
+export function useEventViewProject(
+  eventView: EventView,
+  projects: Project[],
+  project?: string
+) {
   return useMemo(() => {
     if (!defined(eventView)) {
       return undefined;
     }
 
+    if (defined(project)) {
+      return projects.find(proj => proj.id === project);
+    }
+
     const projectId = String(eventView.project[0]);
 
     return projects.find(proj => proj.id === projectId);
-  }, [eventView, projects]);
+  }, [eventView, projects, project]);
 }

static/app/views/performance/transactionSummary/transactionThresholdModal.tsx

@@ -55,6 +55,7 @@ function TransactionThresholdModal({
   organization,
   closeModal,
   onApply,
+  project: projectProp,
   projects,
   transactionName,
   transactionThreshold,
@@ -66,7 +67,7 @@ function TransactionThresholdModal({
   const [metric, setMetric] = useState<TransactionThresholdMetric | undefined>(
     transactionThresholdMetric
   );
-  const project = useEventViewProject(eventView, projects);
+  const project = useEventViewProject(eventView, projects, projectProp);
 
   const handleApply = (event: React.FormEvent) => {
     event.preventDefault();
@@ -148,6 +149,14 @@ function TransactionThresholdModal({
             const errorMessage = err.responseJSON?.threshold ?? null;
             addErrorMessage(errorMessage);
           });
+      })
+      .catch(err => {
+        let errorMessage =
+          err.responseJSON?.threshold ?? err.responseJSON?.non_field_errors ?? null;
+        if (Array.isArray(errorMessage)) {
+          errorMessage = errorMessage[0];
+        }
+        addErrorMessage(errorMessage);
       });
   };