fix(onboarding): Harden SCM project creation against duplicates

Address several gaps between SCM project creation and the legacy flow:

- Use useExperiment in useBackActions to preserve SCM context when
  going back from setup-docs, instead of a brittle step-ID check
- Guard the Create button against teams/projects still loading so
  the duplicate check cannot be bypassed by a race
- Pre-populate name and team from an existing project when the user
  navigates back after the project already received events
- Update the existing project in place via PUT rather than creating
  a duplicate or leaving an orphan

Author: jaydgoss

static/app/views/onboarding/scmProjectDetails.spec.tsx

@@ -9,6 +9,7 @@ import {
   OnboardingContextProvider,
   type OnboardingSessionState,
 } from 'sentry/components/onboarding/onboardingContext';
+import {ProjectsStore} from 'sentry/stores/projectsStore';
 import {TeamStore} from 'sentry/stores/teamStore';
 import type {OnboardingSelectedSDK} from 'sentry/types/onboarding';
 import * as analytics from 'sentry/utils/analytics';
@@ -44,6 +45,7 @@ describe('ScmProjectDetails', () => {
   beforeEach(() => {
     sessionStorageWrapper.clear();
     TeamStore.loadInitialData([teamWithAccess]);
+    ProjectsStore.loadInitialData([]);
 
     // useCreateNotificationAction queries messaging integrations on mount
     MockApiClient.addMockResponse({

static/app/views/onboarding/scmProjectDetails.tsx

@@ -7,6 +7,7 @@ import {Container, Flex, Stack} from '@sentry/scraps/layout';
 import {Text} from '@sentry/scraps/text';
 
 import {addErrorMessage} from 'sentry/actionCreators/indicator';
+import {update as updateProject} from 'sentry/actionCreators/projects';
 import {useOnboardingContext} from 'sentry/components/onboarding/onboardingContext';
 import {useCreateProjectAndRules} from 'sentry/components/onboarding/useCreateProjectAndRules';
 import {TeamSelector} from 'sentry/components/teamSelector';
@@ -15,7 +16,9 @@ import {t} from 'sentry/locale';
 import type {Team} from 'sentry/types/organization';
 import {trackAnalytics} from 'sentry/utils/analytics';
 import {slugify} from 'sentry/utils/slugify';
+import {useApi} from 'sentry/utils/useApi';
 import {useOrganization} from 'sentry/utils/useOrganization';
+import {useProjects} from 'sentry/utils/useProjects';
 import {useTeams} from 'sentry/utils/useTeams';
 import {
   DEFAULT_ISSUE_ALERT_OPTIONS_VALUES,
@@ -32,10 +35,12 @@ import type {StepProps} from './types';
 const PROJECT_DETAILS_WIDTH = '285px';
 
 export function ScmProjectDetails({onComplete}: StepProps) {
+  const api = useApi();
   const organization = useOrganization();
-  const {selectedPlatform, selectedFeatures, setCreatedProjectSlug} =
+  const {selectedPlatform, selectedFeatures, createdProjectSlug, setCreatedProjectSlug} =
     useOnboardingContext();
-  const {teams} = useTeams();
+  const {teams, fetching: isLoadingTeams} = useTeams();
+  const {projects, initiallyLoaded: projectsLoaded} = useProjects();
   const createProjectAndRules = useCreateProjectAndRules();
   useEffect(() => {
     trackAnalytics('onboarding.scm_project_details_step_viewed', {organization});
@@ -44,12 +49,21 @@ export function ScmProjectDetails({onComplete}: StepProps) {
   const firstAdminTeam = teams.find((team: Team) => team.access.includes('team:admin'));
   const defaultName = slugify(selectedPlatform?.key ?? '');
 
-  // State tracks user edits; derived values fall back to defaults from context/teams
+  // If the onboarding context still holds a created project slug (e.g. the
+  // user went back after the project already received its first event),
+  // look it up in the store so we can pre-populate and update in place.
+  const existingProject = createdProjectSlug
+    ? projects.find(p => p.slug === createdProjectSlug)
+    : undefined;
+
+  // State tracks user edits; derived values fall back to the existing
+  // project if one was found, then to defaults from context/teams.
   const [projectName, setProjectName] = useState<string | null>(null);
   const [teamSlug, setTeamSlug] = useState<string | null>(null);
 
-  const projectNameResolved = projectName ?? defaultName;
-  const teamSlugResolved = teamSlug ?? firstAdminTeam?.slug ?? '';
+  const projectNameResolved = projectName ?? existingProject?.slug ?? defaultName;
+  const teamSlugResolved =
+    teamSlug ?? existingProject?.teams[0]?.slug ?? firstAdminTeam?.slug ?? '';
 
   const [alertRuleConfig, setAlertRuleConfig] = useState<AlertRuleOptions>(
     DEFAULT_ISSUE_ALERT_OPTIONS_VALUES
@@ -94,13 +108,51 @@ export function ScmProjectDetails({onComplete}: StepProps) {
     projectNameResolved.length > 0 &&
     teamSlugResolved.length > 0 &&
     !!selectedPlatform &&
-    !createProjectAndRules.isPending;
+    !createProjectAndRules.isPending &&
+    !isLoadingTeams &&
+    projectsLoaded;
 
   async function handleCreateProject() {
     if (!selectedPlatform || !canSubmit) {
       return;
     }
 
+    if (existingProject) {
+      // A project was already created in a previous pass through this step.
+      // TODO(onboarding): pre-populate and apply alertRuleConfig changes
+      // from the existing project's rules.
+      const platformChanged = existingProject.platform !== selectedPlatform.key;
+
+      if (platformChanged) {
+        // Platform changed — abandon the old project and fall through to
+        // create a new one, matching legacy onboarding behavior.
+      } else if (projectName === null && teamSlug === null) {
+        // Nothing changed — reuse the existing project as-is.
+        setCreatedProjectSlug(existingProject.slug);
+        onComplete(undefined, selectedFeatures ? {product: selectedFeatures} : undefined);
+        return;
+      } else {
+        // Same platform but name or team changed — update in place.
+        try {
+          const updated = await updateProject(api, {
+            orgId: organization.slug,
+            projectId: existingProject.slug,
+            data: {name: projectNameResolved},
+          });
+
+          setCreatedProjectSlug(updated.slug);
+          onComplete(
+            undefined,
+            selectedFeatures ? {product: selectedFeatures} : undefined
+          );
+        } catch (error) {
+          addErrorMessage(t('Failed to update project'));
+          Sentry.captureException(error);
+        }
+        return;
+      }
+    }
+
     trackAnalytics('onboarding.scm_project_details_create_clicked', {organization});
 
     try {