fix(onboarding): Skip duplicate project creation in SCM steps

When a user goes back from setup-docs after the project has already
received its first event, the project is not deleted. Without this
guard, clicking Continue/Create again would attempt to create a
duplicate. Check the projects store first and reuse the existing
project, mirroring the useConfigureSdk logic.

Also use useExperiment for the SCM back-action check to stay
consistent with how onboarding.tsx reads the experiment flag.

Refs VDY-82

Author: jaydgoss

static/app/views/onboarding/scmPlatformFeatures.tsx

@@ -27,6 +27,7 @@ import type {PlatformIntegration, PlatformKey} from 'sentry/types/project';
 import {trackAnalytics} from 'sentry/utils/analytics';
 import {isDisabledGamingPlatform} from 'sentry/utils/platform';
 import {useOrganization} from 'sentry/utils/useOrganization';
+import {useProjects} from 'sentry/utils/useProjects';
 import {useTeams} from 'sentry/utils/useTeams';
 import {ScmFeatureSelectionCards} from 'sentry/views/onboarding/components/scmFeatureSelectionCards';
 import {ScmPlatformCard} from 'sentry/views/onboarding/components/scmPlatformCard';
@@ -93,6 +94,7 @@ export function ScmPlatformFeatures({onComplete}: StepProps) {
   } = useOnboardingContext();
 
   const {teams} = useTeams();
+  const {projects} = useProjects();
   const createProject = useCreateProject();
   const hasProjectDetailsStep = organization.features.includes(
     'onboarding-scm-project-details'
@@ -338,6 +340,16 @@ export function ScmPlatformFeatures({onComplete}: StepProps) {
         return;
       }
 
+      // If a project for this platform already exists (e.g. the user went
+      // back after the project had already received its first event), skip
+      // creation and reuse it — mirrors useConfigureSdk logic.
+      const existingProject = projects.find(p => p.slug === platform.key);
+      if (existingProject) {
+        setCreatedProjectSlug(existingProject.slug);
+        onComplete(undefined, {product: currentFeatures});
+        return;
+      }
+
       const firstAdminTeam = teams.find((team: Team) =>
         team.access.includes('team:admin')
       );

static/app/views/onboarding/scmProjectDetails.tsx

@@ -16,6 +16,7 @@ import type {Team} from 'sentry/types/organization';
 import {trackAnalytics} from 'sentry/utils/analytics';
 import {slugify} from 'sentry/utils/slugify';
 import {useOrganization} from 'sentry/utils/useOrganization';
+import {useProjects} from 'sentry/utils/useProjects';
 import {useTeams} from 'sentry/utils/useTeams';
 import {
   DEFAULT_ISSUE_ALERT_OPTIONS_VALUES,
@@ -36,6 +37,7 @@ export function ScmProjectDetails({onComplete}: StepProps) {
   const {selectedPlatform, selectedFeatures, setCreatedProjectSlug} =
     useOnboardingContext();
   const {teams} = useTeams();
+  const {projects} = useProjects();
   const createProjectAndRules = useCreateProjectAndRules();
   useEffect(() => {
     trackAnalytics('onboarding.scm_project_details_step_viewed', {organization});
@@ -101,6 +103,16 @@ export function ScmProjectDetails({onComplete}: StepProps) {
       return;
     }
 
+    // If a project for this name already exists (e.g. the user went back
+    // after the project had already received its first event), skip
+    // creation and reuse it — mirrors useConfigureSdk logic.
+    const existingProject = projects.find(p => p.slug === projectNameResolved);
+    if (existingProject) {
+      setCreatedProjectSlug(existingProject.slug);
+      onComplete(undefined, selectedFeatures ? {product: selectedFeatures} : undefined);
+      return;
+    }
+
     trackAnalytics('onboarding.scm_project_details_create_clicked', {organization});
 
     try {

static/app/views/onboarding/useBackActions.tsx

@@ -10,6 +10,7 @@ import {handleXhrErrorResponse} from 'sentry/utils/handleXhrErrorResponse';
 import type {RequestError} from 'sentry/utils/requestError/requestError';
 import {normalizeUrl} from 'sentry/utils/url/normalizeUrl';
 import {useApi} from 'sentry/utils/useApi';
+import {useExperiment} from 'sentry/utils/useExperiment';
 import {useOrganization} from 'sentry/utils/useOrganization';
 import type {StepDescriptor} from 'sentry/views/onboarding/types';
 
@@ -33,6 +34,9 @@ export function useBackActions({
   const api = useApi();
   const organization = useOrganization();
   const onboardingContext = useOnboardingContext();
+  const {inExperiment: hasScmOnboarding} = useExperiment({
+    feature: 'onboarding-scm-experiment',
+  });
   const currentStep = onboardingSteps[stepIndex];
 
   const deleteRecentCreatedProject = useCallback(
@@ -118,23 +122,22 @@ export function useBackActions({
         // store data and skip project creation.
         // In the SCM flow, preserve context so the user keeps their SCM
         // connection, repo selection, and feature choices.
-        await deleteRecentCreatedProject(
-          organization.features.includes('onboarding-scm-experiment')
-        );
+        await deleteRecentCreatedProject(hasScmOnboarding);
       }
 
       if (!browserBackButton) {
         goToStep(prevStep);
       }
     },
     [
-      goToStep,
+      currentStep,
       organization,
-      onboardingContext,
       isRecentCreatedProjectActive,
       recentCreatedProject,
-      currentStep,
+      onboardingContext,
+      goToStep,
       deleteRecentCreatedProject,
+      hasScmOnboarding,
     ]
   );