refactor(sdk): centralise store validation and remove internal selector export

- add assertValidStore() and getClientForReducerPath() to sdk-store so
  davinci and journey no longer duplicate the isSdkStoreHandle guard
- davinci() and journey() now return GenericError on invalid store arg
  instead of throwing, matching the oidc() error contract
- add conflicting-client guard to journey() via getClientForReducerPath
- remove createWellknownSelector from sdk-store public index (internal detail)
- conflictingClientId in oidc-client delegates to getClientForReducerPath
- update e2e apps to handle new union return types from davinci() and journey()

Author: ryanbas21

e2e/davinci-app/main.ts

@@ -13,7 +13,6 @@ import type {
   Collectors,
   CustomLogger,
   DaVinciConfig,
-  DavinciClient,
   GetClient,
   InternalErrorResponse,
   NodeStates,
@@ -88,7 +87,11 @@ const requestMiddleware: RequestMiddleware<'DAVINCI_NEXT' | 'DAVINCI_START'>[] =
 const urlParams = new URLSearchParams(window.location.search);
 
 (async () => {
-  const davinciClient: DavinciClient = await davinci({ config, logger, requestMiddleware });
+  const davinciResult = await davinci({ config, logger, requestMiddleware });
+  if ('error' in davinciResult) {
+    throw new Error(`Failed to initialize davinci client: ${davinciResult.error}`);
+  }
+  const davinciClient = davinciResult;
   const oidcResult = await oidc({ config: config as OidcConfig });
   if ('error' in oidcResult) {
     throw new Error(`Failed to initialize oidc client: ${oidcResult.error}`);

e2e/journey-app/main.ts

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2025-2026 Ping Identity Corporation. All rights reserved.
+ * Copyright (c) 2025 - 2026 Ping Identity Corporation. All rights reserved.
  *
  * This software may be modified and distributed under the terms
  * of the MIT license. See the LICENSE file for details.
@@ -8,7 +8,7 @@ import './style.css';
 
 import { journey } from '@forgerock/journey-client';
 
-import type { JourneyClient, RequestMiddleware } from '@forgerock/journey-client/types';
+import type { RequestMiddleware } from '@forgerock/journey-client/types';
 
 import { renderCallbacks } from './callback-map.js';
 import { renderDeleteDevicesSection } from './components/delete-device.js';
@@ -62,15 +62,14 @@ if (searchParams.get('middleware') === 'true') {
   const formEl = document.getElementById('form') as HTMLFormElement;
   const journeyEl = document.getElementById('journey') as HTMLDivElement;
 
-  let journeyClient: JourneyClient;
-  try {
-    journeyClient = await journey({ config: config, requestMiddleware });
-  } catch (error) {
-    const message = error instanceof Error ? error.message : 'Unknown error';
+  const journeyResult = await journey({ config: config, requestMiddleware });
+  if ('error' in journeyResult) {
+    const message = journeyResult.error;
     console.error('Failed to initialize journey client:', message);
     errorEl.textContent = message;
     return;
   }
+  const journeyClient = journeyResult;
   let step = await journeyClient.start({ journey: journeyName });
 
   function renderError() {