fix(settings): Remember last selected project in settings v3 rail

static/app/views/navigation/constants.tsx

@@ -34,3 +34,7 @@ export const SETTINGS_PATH_PREFIX = '/settings';
 // Scoped by organization so "Back to app" never returns to another organization.
 export const getSettingsReturnPathKey = (organizationSlug: string) =>
   `settings-return-path:${organizationSlug}`;
+
+// The project the settings rail links to after the user leaves project settings.
+export const getSettingsLastProjectKey = (organizationSlug: string) =>
+  `settings-last-project:${organizationSlug}`;

static/app/views/navigation/index.desktop.spec.tsx

@@ -17,7 +17,10 @@ import {
 import {ConfigStore} from 'sentry/stores/configStore';
 import {ProjectsStore} from 'sentry/stores/projectsStore';
 import {Navigation} from 'sentry/views/navigation';
-import {NAVIGATION_SIDEBAR_COLLAPSED_LOCAL_STORAGE_KEY} from 'sentry/views/navigation/constants';
+import {
+  NAVIGATION_SIDEBAR_COLLAPSED_LOCAL_STORAGE_KEY,
+  getSettingsLastProjectKey,
+} from 'sentry/views/navigation/constants';
 import {PrimaryNavigationContextProvider} from 'sentry/views/navigation/primaryNavigationContext';
 
 const ALL_AVAILABLE_FEATURES = [
@@ -472,6 +475,86 @@ describe('desktop navigation', () => {
       }
     );
 
+    it('returns to the last selected project after visiting org settings', async () => {
+      const {router} = render(
+        <PrimaryNavigationContextProvider>
+          <Navigation />
+        </PrimaryNavigationContextProvider>,
+        navigationContext({
+          organization: settingsV3,
+          initialRouterConfig: {
+            location: {pathname: '/settings/org-slug/projects/project-slug/'},
+            routes: ['/settings/:orgId/', '/settings/:orgId/projects/:projectId/'],
+          },
+        })
+      );
+
+      await userEvent.click(screen.getByRole('button', {name: 'Select a project'}));
+      await userEvent.click(await screen.findByRole('option', {name: 'second-project'}));
+      expect(router.location.pathname).toBe(
+        '/settings/org-slug/projects/second-project/'
+      );
+
+      await userEvent.click(screen.getByRole('link', {name: 'Org'}));
+      expect(router.location.pathname).toBe('/settings/org-slug/');
+      expect(screen.getByRole('link', {name: 'Project'})).toHaveAttribute(
+        'href',
+        '/settings/org-slug/projects/second-project/'
+      );
+
+      await userEvent.click(screen.getByRole('link', {name: 'Project'}));
+      expect(router.location.pathname).toBe(
+        '/settings/org-slug/projects/second-project/'
+      );
+    });
+
+    it('links to the remembered project by ID after it was renamed', async () => {
+      localStorage.setItem(getSettingsLastProjectKey('org-slug'), JSON.stringify('999'));
+      ProjectsStore.loadInitialData([
+        ProjectFixture(),
+        ProjectFixture({id: '999', slug: 'renamed-project'}),
+      ]);
+      render(
+        <PrimaryNavigationContextProvider>
+          <Navigation />
+        </PrimaryNavigationContextProvider>,
+        navigationContext({
+          organization: settingsV3,
+          initialRouterConfig: {location: {pathname: '/settings/org-slug/'}},
+        })
+      );
+
+      await waitFor(() =>
+        expect(screen.getByRole('link', {name: 'Project'})).toHaveAttribute(
+          'href',
+          '/settings/org-slug/projects/renamed-project/'
+        )
+      );
+    });
+
+    it('falls back to the first project when the remembered one is unavailable', async () => {
+      localStorage.setItem(
+        getSettingsLastProjectKey('org-slug'),
+        JSON.stringify('12345')
+      );
+      render(
+        <PrimaryNavigationContextProvider>
+          <Navigation />
+        </PrimaryNavigationContextProvider>,
+        navigationContext({
+          organization: settingsV3,
+          initialRouterConfig: {location: {pathname: '/settings/org-slug/'}},
+        })
+      );
+
+      await waitFor(() =>
+        expect(screen.getByRole('link', {name: 'Project'})).toHaveAttribute(
+          'href',
+          '/settings/org-slug/projects/project-slug/'
+        )
+      );
+    });
+
     it('switches from project key details to the new project key list', async () => {
       const {router} = render(
         <PrimaryNavigationContextProvider>

static/app/views/navigation/navigation.tsx

@@ -1,4 +1,11 @@
-import {Fragment, type PropsWithChildren, type RefObject, useMemo, useRef} from 'react';
+import {
+  Fragment,
+  type PropsWithChildren,
+  type RefObject,
+  useEffect,
+  useMemo,
+  useRef,
+} from 'react';
 import {mergeProps} from '@react-aria/utils';
 import {IconArrow} from '@sentry/icons/arrow';
 import {IconBuilding} from '@sentry/icons/building';
@@ -22,6 +29,7 @@ import Feature from 'sentry/components/acl/feature';
 import {ErrorBoundary} from 'sentry/components/errorBoundary';
 import {Override} from 'sentry/components/override';
 import {t} from 'sentry/locale';
+import {useLocalStorageState} from 'sentry/utils/useLocalStorageState';
 import {useOrganization} from 'sentry/utils/useOrganization';
 import {useProjects} from 'sentry/utils/useProjects';
 import {getReturnPath} from 'sentry/utils/useReturnPath';
@@ -35,6 +43,7 @@ import {
   NAVIGATION_SIDEBAR_SECONDARY_WIDTH_LOCAL_STORAGE_KEY,
   PRIMARY_SIDEBAR_WIDTH,
   SECONDARY_SIDEBAR_WIDTH,
+  getSettingsLastProjectKey,
   getSettingsReturnPathKey,
 } from 'sentry/views/navigation/constants';
 import {
@@ -205,7 +214,22 @@ export function SettingsPrimaryNavigationItems({
 }) {
   const {projects} = useProjects();
   const {scope: activeScope, projectSlug: activeProjectSlug} = useSettingsScope();
-  const projectSlug = activeProjectSlug ?? projects[0]?.slug;
+  // Stored by ID, not slug, so renaming the project does not lose it.
+  const [lastProjectId, setLastProjectId] = useLocalStorageState<string | null>(
+    getSettingsLastProjectKey(organizationSlug),
+    null
+  );
+  const activeProjectId = projects.find(({slug}) => slug === activeProjectSlug)?.id;
+
+  useEffect(() => {
+    if (activeProjectId && activeProjectId !== lastProjectId) {
+      setLastProjectId(activeProjectId);
+    }
+  }, [activeProjectId, lastProjectId, setLastProjectId]);
+
+  // The remembered project can be deleted or lose access since it was stored.
+  const rememberedProjectSlug = projects.find(({id}) => id === lastProjectId)?.slug;
+  const projectSlug = activeProjectSlug ?? rememberedProjectSlug ?? projects[0]?.slug;
   const projectSettingsPath = `/settings/${organizationSlug}/projects/`;
   const items = [
     {