[Embeddables] Decouple fetching from search sessions (#240333)

Closes #239610

## Summary

This PR decouples fetching from search session IDs - i.e. we no longer
need the search session ID to change in order to trigger a refetch. This
unblocks #233124, since making a
selection in a section-scoped control should **not** trigger a new
search session but it **should** cause a refetch for the targeted
panels. This is also just a cleaner implementation overall, since search
sessions should **not** drive fetching.

Note that, in order to ensure that fetching still happens **after** the
search session ID changes (so that embeddables receive the up-to-date ID
and no double fetch happens), I had to add an async callback that allows
the Dashboard to let the `fetch$` observable know when the search
session ID is stable.

### Checklist

- [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.

---------

Co-authored-by: kibanamachine <[email protected]>

Author: Heenawter

src/platform/packages/shared/kbn-unified-histogram/components/chart/chart.tsx

@@ -72,6 +72,7 @@ export interface UnifiedHistogramChartProps {
   isPlainRecord?: boolean;
   lensVisService: LensVisService;
   relativeTimeRange?: TimeRange;
+  lastReloadRequestTime?: number;
   request?: UnifiedHistogramRequestContext;
   hits?: UnifiedHistogramHitsContext;
   chart?: UnifiedHistogramChartContext;
@@ -104,6 +105,7 @@ export function UnifiedHistogramChart({
   dataView,
   requestParams,
   relativeTimeRange: originalRelativeTimeRange,
+  lastReloadRequestTime,
   request,
   hits,
   chart,
@@ -223,6 +225,7 @@ export function UnifiedHistogramChart({
     visContext,
     esqlVariables,
     onLoad,
+    lastReloadRequestTime,
   });
 
   const { chartToolbarCss, histogramCss } = useChartStyles(chartVisible);

src/platform/packages/shared/kbn-unified-histogram/components/chart/hooks/use_lens_props.ts

@@ -31,6 +31,7 @@ export type LensProps = Pick<
   | 'searchSessionId'
   | 'executionContext'
   | 'onLoad'
+  | 'lastReloadRequestTime'
 >;
 
 export const useLensProps = ({
@@ -40,13 +41,15 @@ export const useLensProps = ({
   visContext,
   esqlVariables,
   onLoad,
+  lastReloadRequestTime,
 }: {
   request?: UnifiedHistogramRequestContext;
   getTimeRange: () => TimeRange;
   fetch$: Observable<UnifiedHistogramInputMessage>;
   visContext?: UnifiedHistogramVisContext;
   esqlVariables?: ESQLControlVariable[];
   onLoad: (isLoading: boolean, adapters: Partial<DefaultInspectorAdapters> | undefined) => void;
+  lastReloadRequestTime?: number;
 }) => {
   const buildLensProps = useCallback(() => {
     if (!visContext) {
@@ -63,9 +66,17 @@ export const useLensProps = ({
         attributes,
         esqlVariables,
         onLoad,
+        lastReloadRequestTime,
       }),
     };
-  }, [visContext, request?.searchSessionId, getTimeRange, esqlVariables, onLoad]);
+  }, [
+    visContext,
+    request?.searchSessionId,
+    getTimeRange,
+    esqlVariables,
+    onLoad,
+    lastReloadRequestTime,
+  ]);
 
   // Initialize with undefined to avoid rendering Lens until a fetch has been triggered
   const [lensPropsContext, setLensPropsContext] = useState<ReturnType<typeof buildLensProps>>();
@@ -85,12 +96,14 @@ export const getLensProps = ({
   attributes,
   esqlVariables,
   onLoad,
+  lastReloadRequestTime,
 }: {
   searchSessionId?: string;
   getTimeRange: () => TimeRange;
   attributes: TypedLensByValueInput['attributes'];
   esqlVariables?: ESQLControlVariable[];
   onLoad: (isLoading: boolean, adapters: Partial<DefaultInspectorAdapters> | undefined) => void;
+  lastReloadRequestTime?: number;
 }): LensProps => ({
   id: 'unifiedHistogramLensComponent',
   viewMode: 'view',
@@ -103,4 +116,5 @@ export const getLensProps = ({
     description: 'fetch chart data and total hits',
   },
   onLoad,
+  lastReloadRequestTime,
 });

src/platform/packages/shared/kbn-unified-histogram/hooks/use_unified_histogram.ts

@@ -95,6 +95,10 @@ export type UseUnifiedHistogramProps = Omit<UnifiedHistogramStateOptions, 'servi
    * The relative time range, used when timeRange is an absolute range (e.g. for edit visualization button)
    */
   relativeTimeRange?: TimeRange;
+  /**
+   * The timestamp of the last data request
+   */
+  lastReloadRequestTime?: number;
   /**
    * The current columns
    */