@@ -0,0 +1,16 @@
+---
+'@hyperdx/app': patch
+---
+
+feat(dashboards): opt-in linked (faceted) filter values
+
+Dashboard and Kubernetes filter bars gain a "link filters" toggle (the
+bidirectional-arrow button at the end of the bar). When enabled, each filter
+dropdown only shows values that co-occur with the other current selections —
+e.g. picking a `cluster` narrows the `namespace` dropdown to namespaces in that
+cluster (the K8s bar also factors in the free-text search). A filter never
+constrains its own options, so multi-select still works. It is off by default
+because contingent value lookups can't use the cheap per-key rollups and are
+more expensive at scale; when on, all of a source's facets are computed in a
+single `groupUniqArrayIf` scan rather than one query per filter. Search-page
+filters are unaffected.
@@ -1,9 +1,10 @@
-import { useMemo } from 'react';
+import { useMemo, useState } from 'react';
 import { FilterState } from '@hyperdx/common-utils/dist/filters';
 import { DashboardFilter } from '@hyperdx/common-utils/dist/types';
 import { Group, Stack, Text, Tooltip } from '@mantine/core';
 import { IconAlertTriangle, IconHelp, IconRefresh } from '@tabler/icons-react';
 
+import { FilterLinkToggle } from './components/FilterLinkToggle';
 import { VirtualMultiSelect } from './components/VirtualMultiSelect/VirtualMultiSelect';
 import { useDashboardFilterValues } from './hooks/useDashboardFilterValues';
 
@@ -64,10 +65,10 @@ const DashboardFilterSelect = ({
           placeholder={value.length === 0 ? filter.name : undefined}
           values={value}
           data={valuesOrEmptyMemo}
-          // Disable only while values are genuinely loading. A completed query
-          // that returned no rows (or failed) must stay interactive so the user
-          // can still clear/adjust the selection instead of being stuck.
-          disabled={isLoading}
+          // Surface loading as a dropdown hint rather than disabling the control,
+          // so a completed/empty/failed query stays interactive and the user can
+          // still clear or adjust the selection.
+          loading={isLoading}
           onChange={onChange}
           data-testid={`dashboard-filter-select-${filter.name}`}
         />
@@ -89,13 +90,21 @@ const DashboardFilters = ({
   filterValues,
   onSetFilterValue,
 }: DashboardFilterProps) => {
+  // "Link" mode (opt-in, off by default): each dropdown's values are narrowed by
+  // the others' selections. Off by default because contingent value lookups
+  // can't use the cheap per-key rollups and are more expensive at scale. When
+  // on, all of a source's facets are computed in a single groupUniqArrayIf scan.
+  const [linked, setLinked] = useState(false);
+
   const {
     data: filterValuesById,
     erroredFilterIds,
     isFetching,
   } = useDashboardFilterValues({
     filters,
     dateRange,
+    // Only narrow by sibling selections when linked.
+    filterValues: linked ? filterValues : {},
   });
 
   return (
@@ -108,7 +117,7 @@ const DashboardFilters = ({
           : [];
         // Fall back to the hook-level fetching state only until this filter's
         // query has produced an entry; once it has (even with empty values),
-        // honor its own loading flag so a finished query never stays disabled.
+        // honor its own loading flag.
         const isLoadingValues = queriedFilterValues
           ? queriedFilterValues.isLoading
           : isFetching;
@@ -124,6 +133,19 @@ const DashboardFilters = ({
           />
         );
       })}
+      {filters.length >= 2 && (
+        <Stack gap={2} justify="flex-end">
+          {/* Spacer to align the toggle with the inputs (filters have a label row above). */}
+          <Text size="xs" c="transparent" aria-hidden>
+            &nbsp;
+          </Text>
+          <FilterLinkToggle
+            linked={linked}
+            onChange={setLinked}
+            data-testid="dashboard-filters-link-toggle"
+          />
+        </Stack>
+      )}
       {isFetching && <IconRefresh className="spin-animate" size={12} />}
     </Group>
   );
 
@@ -0,0 +1,56 @@
+import type { CSSProperties } from 'react';
+import { ActionIcon, Tooltip } from '@mantine/core';
+import { IconArrowsLeftRight } from '@tabler/icons-react';
+
+type FilterLinkToggleProps = {
+  linked: boolean;
+  onChange: (linked: boolean) => void;
+  'data-testid'?: string;
+};
+
+/**
+ * Opt-in toggle that "links" a set of filter dropdowns so each one's selectable
+ * values are narrowed by the others' current selections (faceted / filter-aware
+ * values). Off by default because contingent value lookups can't be served from
+ * the cheap per-key rollups and are far more expensive at scale.
+ */
+export function FilterLinkToggle({
+  linked,
+  onChange,
+  'data-testid': dataTestId = 'filter-link-toggle',
+}: FilterLinkToggleProps) {
+  return (
+    <Tooltip
+      withinPortal
+      multiline
+      w={250}
+      label={
+        linked
+          ? 'Filters are linked: each dropdown only shows values that match the other selections. Click to unlink.'
+          : 'Link filters: narrow each dropdown to values that match the other selections (filter-aware). May be slower on large datasets.'
+      }
+    >
+      <ActionIcon
+        variant="subtle"
+        // Active state: a high-contrast inverted "pill" via theme tokens (never
+        // green, on any theme) so linked mode is clearly visible; off is the
+        // plain subtle icon. Overrides Mantine's ActionIcon CSS vars inline.
+        style={
+          linked
+            ? ({
+                '--ai-bg': 'var(--color-bg-inverted)',
+                '--ai-hover': 'var(--color-bg-inverted)',
+                '--ai-color': 'var(--color-text-inverted)',
+              } as CSSProperties)
+            : undefined
+        }
+        onClick={() => onChange(!linked)}
+        aria-label="Link filters"
+        aria-pressed={linked}
+        data-testid={dataTestId}
+      >
+        <IconArrowsLeftRight size={16} />
+      </ActionIcon>
+    </Tooltip>
+  );
+}