From 8c5497d95ebb50c4da274a17ff16bae9bfd96d94 Mon Sep 17 00:00:00 2001
From: Carlos Crespo <crespocarlos@users.noreply.github.com>
Date: Wed, 29 Oct 2025 13:01:59 +0100
Subject: [PATCH] [Metrics][Discover] Discover input$ observable emission lost
 fix (#241092)

fixes [240429](https://github.com/elastic/kibana/issues/240429)

## Summary

This PR fixes a bug where the Discover `input$` observable emissions
were not always captured by the Metrics Experience, depending on the
interval between the observable emission and the subscription in the
`use_lens_props` hook.

### Before

![obs-bug](https://github.com/user-attachments/assets/a45d26ec-c3ee-4f67-9484-fb5864f14b3c)

### After

![obs-fix](https://github.com/user-attachments/assets/0074ec26-f2b2-4535-847b-fff8a466fef5)

## How to test
- Start a local Kibana instance and point it to an oblt cluster - the
bug is more likely to occur when the performance is worse
```yml
feature_flags.overrides:
  metricsExperienceEnabled: true
 ```
- Navigate to Discover and Switch to ESQL mode
- Change the date picker to a range with no metrics data, then change it again to a range where metrics data is available.

(cherry picked from commit 2ad7f51bc95dd4392a4c6cdec16a25650762aefc)

# Conflicts:
#	src/platform/packages/shared/kbn-unified-metrics-grid/src/components/metrics_experience_grid.tsx
---
 .../src/components/metrics_experience_grid.tsx        | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/platform/packages/shared/kbn-unified-metrics-grid/src/components/metrics_experience_grid.tsx b/src/platform/packages/shared/kbn-unified-metrics-grid/src/components/metrics_experience_grid.tsx
index 9a2bcee1dea89..34f672d913e82 100644
--- a/src/platform/packages/shared/kbn-unified-metrics-grid/src/components/metrics_experience_grid.tsx
+++ b/src/platform/packages/shared/kbn-unified-metrics-grid/src/components/metrics_experience_grid.tsx
@@ -22,7 +22,7 @@ import {
   useEuiTheme,
   type EuiFlexGridProps,
 } from '@elastic/eui';
-import { Subject } from 'rxjs';
+import { Subject, shareReplay } from 'rxjs';
 import { PAGE_SIZE } from '../common/constants';
 import { MetricsGrid } from './metrics_grid';
 import { Pagination } from './pagination';
@@ -62,11 +62,18 @@ export const MetricsExperienceGrid = ({
     [originalInput$]
   );
 
-  const discoverFetch$ = useFetch({
+  const baseFetch$ = useFetch({
     input$,
     beforeFetch: updateTimeRange,
   });
 
+  const discoverFetch$ = useMemo(
+    // Buffer and replay emissions to child components that subscribe in later useEffects
+    // without this, child components would miss emissions that occurred before they subscribed
+    () => baseFetch$.pipe(shareReplay({ bufferSize: 1, refCount: false })),
+    [baseFetch$]
+  );
+
   const indexPattern = useMemo(() => dataView?.getIndexPattern() ?? 'metrics-*', [dataView]);
   const { data: fields = [], isFetching: isFieldsLoading } = useMetricFieldsQuery({
     index: indexPattern,