[Discover] Persist query mode to local storage (elastic#250388)

## Summary

Closes elastic#200765

When changing between classic and ES|QL mode we persist it in local
storage so the next default session uses that preference.

---

Before (Example with ESQL)


https://github.com/user-attachments/assets/a689c0f9-ff69-4bcb-a8da-108d4693cb56



After (Example with ESQL)


https://github.com/user-attachments/assets/bebc03db-a860-4ec9-9843-5e1f0e53f585




### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [x] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)
- [x] Review the [backport
guidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)
and apply applicable `backport:*` labels.

Author: AlexGPlay

.buildkite/ftr_platform_stateful_configs.yml

@@ -91,6 +91,7 @@ enabled:
   - src/platform/test/functional/apps/discover/group10/config.ts
   - src/platform/test/functional/apps/discover/context_awareness/config.ts
   - src/platform/test/functional/apps/discover/observability/config.ts
+  - src/platform/test/functional/apps/discover/query_mode/config.ts
   - src/platform/test/functional/apps/discover/tabs/config.ts
   - src/platform/test/functional/apps/discover/tabs2/config.ts
   - src/platform/test/functional/apps/discover/tabs3/config.ts

src/platform/plugins/shared/discover/common/constants.ts

@@ -26,6 +26,9 @@ export const getDefaultRowsPerPage = (uiSettings: IUiSettingsClient): number =>
 // local storage key for the ES|QL to Dataviews transition modal
 export const ESQL_TRANSITION_MODAL_KEY = 'data.textLangTransitionModal';
 
+// local storage key for the query mode when starting a new discover session
+export const DISCOVER_QUERY_MODE_KEY = 'discover.defaultQueryMode';
+
 /**
  * The id value used to indicate that a link should open in a new Discover tab.
  * It will be used in the `_tab` URL param to indicate that a new tab should be created.

src/platform/plugins/shared/discover/public/application/main/state_management/redux/actions/initialize_single_tab.ts

@@ -232,6 +232,7 @@ export const initializeSingleTab = createInternalStateAsyncThunk(
     // then get an updated copy of the saved search with the applied initial state
     const initialAppState = getInitialAppState({
       initialUrlState: urlAppState,
+      hasGlobalState: Object.keys(urlGlobalState || {}).length > 0,
       persistedTab,
       dataView,
       services,

src/platform/plugins/shared/discover/public/application/main/state_management/redux/actions/tab_state.ts

@@ -26,6 +26,8 @@ import {
   internalStateSlice,
   type InternalStateThunkActionCreator,
   type TabActionPayload,
+  transitionedFromEsqlToDataView,
+  transitionedFromDataViewToEsql,
 } from '../internal_state';
 import { selectTab } from '../selectors';
 import { selectTabRuntimeState } from '../runtime_state';
@@ -206,6 +208,8 @@ export const transitionFromESQLToDataView: InternalStateThunkActionCreator<
         },
       })
     );
+
+    dispatch(transitionedFromEsqlToDataView({ tabId }));
   };
 
 const clearTimeFieldFromSort = (
@@ -251,6 +255,8 @@ export const transitionFromDataViewToESQL: InternalStateThunkActionCreator<
 
     // clears pinned filters
     dispatch(updateGlobalState({ tabId, globalState: { filters: [] } }));
+
+    dispatch(transitionedFromDataViewToEsql({ tabId }));
   };
 
 /**

src/platform/plugins/shared/discover/public/application/main/state_management/redux/internal_state.ts

@@ -29,6 +29,7 @@ import type { IKbnUrlStateStorage } from '@kbn/kibana-utils-plugin/public';
 import type { ESQLControlVariable } from '@kbn/esql-types';
 import type { DiscoverSession } from '@kbn/saved-search-plugin/common';
 import { isOfAggregateQueryType } from '@kbn/es-query';
+import { DISCOVER_QUERY_MODE_KEY } from '../../../../../common/constants';
 import type { DiscoverCustomizationContext } from '../../../../customizations';
 import type { DiscoverServices } from '../../../../build_services';
 import { type RuntimeStateManager, selectTabRuntimeInternalState } from './runtime_state';
@@ -446,6 +447,14 @@ export const syncLocallyPersistedTabState = createAction<TabActionPayload>(
 
 export const discardFlyoutsOnTabChange = createAction('internalState/discardFlyoutsOnTabChange');
 
+export const transitionedFromEsqlToDataView = createAction<TabActionPayload>(
+  'internalState/transitionedFromEsqlToDataView'
+);
+
+export const transitionedFromDataViewToEsql = createAction<TabActionPayload>(
+  'internalState/transitionedFromDataViewToEsql'
+);
+
 type InternalStateListenerEffect<
   TActionCreator extends PayloadActionCreator<TPayload>,
   TPayload = TActionCreator extends PayloadActionCreator<infer T> ? T : never
@@ -510,6 +519,28 @@ const createMiddleware = (options: InternalStateDependencies) => {
     },
   });
 
+  // This pair of listeners updates the default query mode based on the last used query type (ES|QL vs Data View), we use
+  // this so new discover sessions use that query mode as a default.
+  //
+  // NOTE: In the short term we will add a feature flag to default to ES|QL when there is no existing preference saved.
+  // Right now we use classic - this means that users will have to switch to ES|QL manually the first time if they already
+  // had classic stored as their last used mode.
+  startListening({
+    actionCreator: transitionedFromDataViewToEsql,
+    effect: (action, listenerApi) => {
+      const { services } = listenerApi.extra;
+      services.storage.set(DISCOVER_QUERY_MODE_KEY, 'esql');
+    },
+  });
+
+  startListening({
+    actionCreator: transitionedFromEsqlToDataView,
+    effect: (action, listenerApi) => {
+      const { services } = listenerApi.extra;
+      services.storage.set(DISCOVER_QUERY_MODE_KEY, 'classic');
+    },
+  });
+
   return listenerMiddleware.middleware;
 };