fix(prometheus): set NoStepSubqueryIntervalFn to stop promql subquery segfault (#12720)

#### Description

- A PromQL subquery without a step, for example
`max_over_time(metric[5m:])`, segfaulted the whole query-service. The
engine calls `NoStepSubqueryIntervalFn` for such subqueries, and we
build the engine without it, so the call hits a nil function.
- The bug is present on every PromQL surface, because all of them share
the one engine constructor in `pkg/prometheus/engine.go`: v3 and v5
`query_range`, `/api/v1/query`, the clickhousev2 transpiler, and promql
alert rules. A saved rule with such a subquery crash-loops the instance
on its own schedule.
- The fix sets the callback to 1m. This matches the Prometheus default
global `evaluation_interval`, which upstream wires into this field. One
place fixes every path.
- This is the root cause of the SigNoz/platform-pod#3068 incident. The
instance-hardening request from that incident is tracked in
SigNoz/pulse-pod#308.

#### Issues closed by this PR

Closes SigNoz/platform-pod#3068

#### Additional Information

We audited `EngineOpts` for more bugs of the same class.
`NoStepSubqueryIntervalFn` is the only field the engine calls without a
nil guard; `promql.NewEngine` defaults the other nil-able fields
(`Parser`, `FeatureRegistry`). The remaining gaps against upstream
wiring are not crashes, and we filed them separately:
SigNoz/pulse-pod#305 (`@` modifier and negative offset disabled),
SigNoz/pulse-pod#306 (engine self-metrics not registered),
SigNoz/pulse-pod#307 (active query tracker startup panic risk),
SigNoz/pulse-pod#309 (step guard in the v3 cache), SigNoz/pulse-pod#310
(upstream proposal to fail fast on the nil callback).

Tests for the bug:

- `pkg/prometheus/engine_test.go` — fails with the exact segfault when
the fix is removed.
- `tests/integration/tests/promqlconformance/04_no_step_subquery.py` — a
step-less subquery through `/api/v5/query_range` returns correct values
on both providers, and the service stays up.
- `tests/integration/tests/alerts/04_promql_subquery_no_step.py` — a
promql alert rule with a step-less subquery evaluates and fires.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

frontend/src/components/ExplorerCard/ExplorerCard.tsx

@@ -7,9 +7,8 @@ import axios from 'axios';
 import TextToolTip from 'components/TextToolTip';
 import { SOMETHING_WENT_WRONG } from 'constants/api';
 import { LOCALSTORAGE } from 'constants/localStorage';
-import { QueryParams } from 'constants/query';
 import { useOptionsMenu } from 'container/OptionsMenu';
-import { useGetSearchQueryParam } from 'hooks/queryBuilder/useGetSearchQueryParam';
+import { useGetSavedViewParams } from 'hooks/saveViews/useGetSavedViewParams';
 import { useQueryBuilder } from 'hooks/queryBuilder/useQueryBuilder';
 import { useDeleteView } from 'hooks/saveViews/useDeleteView';
 import { useGetAllViews } from 'hooks/saveViews/useGetAllViews';
@@ -69,9 +68,7 @@ function ExplorerCard({
 		setIsOpen(newOpen);
 	};
 
-	const viewName = useGetSearchQueryParam(QueryParams.viewName) || '';
-
-	const viewKey = useGetSearchQueryParam(QueryParams.viewKey) || '';
+	const { viewName, viewKey } = useGetSavedViewParams();
 
 	const { options } = useOptionsMenu({
 		storageKey:

frontend/src/components/ExplorerCard/constants.ts

@@ -1,5 +1,3 @@
-import { QueryParams } from 'constants/query';
-
 export const ExploreHeaderToolTip = {
 	url: 'https://signoz.io/docs/querying/overview/?utm_source=product&utm_medium=new-query-builder',
 	text: 'More details on how to use query builder',
@@ -9,5 +7,3 @@ export const SaveButtonText = {
 	SAVE_AS_NEW_VIEW: 'Save as new view',
 	SAVE_VIEW: 'Save view',
 };
-
-export type QuerySearchParamNames = QueryParams.viewName | QueryParams.viewKey;

frontend/src/container/ExplorerOptions/ExplorerOptions.tsx

@@ -54,7 +54,7 @@ import {
 } from 'container/OptionsMenu/constants';
 import { OptionsQuery } from 'container/OptionsMenu/types';
 import { ExportDashboard } from 'hooks/dashboard/useExportDashboards';
-import { useGetSearchQueryParam } from 'hooks/queryBuilder/useGetSearchQueryParam';
+import { useGetSavedViewParams } from 'hooks/saveViews/useGetSavedViewParams';
 import { useQueryBuilder } from 'hooks/queryBuilder/useQueryBuilder';
 import { useGetAllViews } from 'hooks/saveViews/useGetAllViews';
 import { useSaveView } from 'hooks/saveViews/useSaveView';
@@ -287,8 +287,7 @@ function ExplorerOptions({
 
 	const compositeQuery = mapCompositeQueryFromQuery(currentQuery, panelType);
 
-	const viewName = useGetSearchQueryParam(QueryParams.viewName) || '';
-	const viewKey = useGetSearchQueryParam(QueryParams.viewKey) || '';
+	const { viewName, viewKey } = useGetSavedViewParams();
 
 	const extraData = viewsData?.data?.data?.find(
 		(view) => view.id === viewKey,

frontend/src/container/LogDetailedView/BodyTitleRenderer.tsx

@@ -15,9 +15,8 @@ import {
 	QUERY_BUILDER_FUNCTIONS,
 } from 'constants/antlrQueryConstants';
 import { FeatureKeys } from 'constants/features';
-import { QueryParams } from 'constants/query';
 import { useActiveLog } from 'hooks/logs/useActiveLog';
-import { useGetSearchQueryParam } from 'hooks/queryBuilder/useGetSearchQueryParam';
+import { useGetSavedViewParams } from 'hooks/saveViews/useGetSavedViewParams';
 import { useQueryBuilder } from 'hooks/queryBuilder/useQueryBuilder';
 import { ICurrentQueryData } from 'hooks/useHandleExplorerTabChange';
 import { useNotifications } from 'hooks/useNotifications';
@@ -50,7 +49,7 @@ function BodyTitleRenderer({
 	const { featureFlags } = useAppContext();
 	const [, setCopy] = useCopyToClipboard();
 	const { notifications } = useNotifications();
-	const viewName = useGetSearchQueryParam(QueryParams.viewName) || '';
+	const { viewName } = useGetSavedViewParams();
 
 	const cleanedNodeKey = removeObjectFromString(nodeKey);
 	const isBodyJsonQueryEnabled =

frontend/src/container/LogDetailedView/TableView/TableViewActions.tsx

@@ -7,13 +7,12 @@ import GroupByIcon from 'assets/CustomIcons/GroupByIcon';
 import cx from 'classnames';
 import CopyClipboardHOC from 'components/Logs/CopyClipboardHOC';
 import { DATE_TIME_FORMATS } from 'constants/dateTimeFormats';
-import { QueryParams } from 'constants/query';
 import { OPERATORS } from 'constants/queryBuilder';
 import ROUTES from 'constants/routes';
 import { ChangeViewFunctionType } from 'container/ExplorerOptions/types';
 import { RESTRICTED_SELECTED_FIELDS } from 'container/LogsFilters/config';
 import { MetricsType } from 'container/MetricsApplication/constant';
-import { useGetSearchQueryParam } from 'hooks/queryBuilder/useGetSearchQueryParam';
+import { useGetSavedViewParams } from 'hooks/saveViews/useGetSavedViewParams';
 import { useQueryBuilder } from 'hooks/queryBuilder/useQueryBuilder';
 import { ICurrentQueryData } from 'hooks/useHandleExplorerTabChange';
 import {
@@ -141,7 +140,7 @@ export default function TableViewActions(
 
 	const { pathname } = useLocation();
 	const { stagedQuery, updateQueriesData } = useQueryBuilder();
-	const viewName = useGetSearchQueryParam(QueryParams.viewName) || '';
+	const { viewName } = useGetSavedViewParams();
 	const { dataType, logType: fieldType } = getFieldAttributes(record.field);
 
 	// there is no option for where clause in old logs explorer and live logs page or infra monitoring

frontend/src/container/LogDetailedView/TableView/__test__/TableViewActions.test.tsx

@@ -1,6 +1,6 @@
 import { fireEvent, render, screen } from '@testing-library/react';
 import { RESTRICTED_SELECTED_FIELDS } from 'container/LogsFilters/config';
-import { useGetSearchQueryParam } from 'hooks/queryBuilder/useGetSearchQueryParam';
+import { useGetSavedViewParams } from 'hooks/saveViews/useGetSavedViewParams';
 import { useQueryBuilder } from 'hooks/queryBuilder/useQueryBuilder';
 import { ExplorerViews } from 'pages/LogsExplorer/utils';
 
@@ -88,7 +88,7 @@ jest.mock('react-router-dom', () => ({
 }));
 
 jest.mock('hooks/queryBuilder/useQueryBuilder');
-jest.mock('hooks/queryBuilder/useGetSearchQueryParam');
+jest.mock('hooks/saveViews/useGetSavedViewParams');
 
 describe('TableViewActions', () => {
 	const TEST_VALUE = 'test value';
@@ -140,8 +140,10 @@ describe('TableViewActions', () => {
 			}),
 		} as any);
 
-		// Default mock for useGetSearchQueryParam
-		jest.mocked(useGetSearchQueryParam).mockReturnValue(null);
+		// Default mock for useGetSavedViewParams
+		jest
+			.mocked(useGetSavedViewParams)
+			.mockReturnValue({ viewName: '', viewKey: '' });
 	});
 
 	it('should render without crashing', () => {
@@ -249,7 +251,9 @@ describe('TableViewActions', () => {
 			updateQueriesData: mockUpdateQueriesData,
 		} as any);
 
-		jest.mocked(useGetSearchQueryParam).mockReturnValue(null);
+		jest
+			.mocked(useGetSavedViewParams)
+			.mockReturnValue({ viewName: '', viewKey: '' });
 
 		render(
 			<TableViewActions

frontend/src/container/LogDetailedView/hooks/useLogAttributeActions.tsx

@@ -3,10 +3,9 @@ import { useLocation } from 'react-router-dom';
 import { CircleMinus, CirclePlus, Layers, RefreshCw } from '@signozhq/icons';
 import { convertFiltersToExpression } from 'components/QueryBuilderV2/utils';
 import { FeatureKeys } from 'constants/features';
-import { QueryParams } from 'constants/query';
 import ROUTES from 'constants/routes';
 import { ChangeViewFunctionType } from 'container/ExplorerOptions/types';
-import { useGetSearchQueryParam } from 'hooks/queryBuilder/useGetSearchQueryParam';
+import { useGetSavedViewParams } from 'hooks/saveViews/useGetSavedViewParams';
 import { useQueryBuilder } from 'hooks/queryBuilder/useQueryBuilder';
 import { ICurrentQueryData } from 'hooks/useHandleExplorerTabChange';
 import { ExplorerViews } from 'pages/LogsExplorer/utils';
@@ -58,7 +57,7 @@ export function useLogAttributeActions({
 	const { pathname } = useLocation();
 	const { stagedQuery, updateQueriesData } = useQueryBuilder();
 	const { featureFlags } = useAppContext();
-	const viewName = useGetSearchQueryParam(QueryParams.viewName) || '';
+	const { viewName } = useGetSavedViewParams();
 
 	const isBodyJsonQueryEnabled =
 		featureFlags?.find((flag) => flag.name === FeatureKeys.USE_JSON_BODY)

frontend/src/hooks/queryBuilder/useGetSearchQueryParam.ts

@@ -1,15 +0,0 @@
-import { useMemo } from 'react';
-import { QuerySearchParamNames } from 'components/ExplorerCard/constants';
-import useUrlQuery from 'hooks/useUrlQuery';
-
-export const useGetSearchQueryParam = (
-	searchParams: QuerySearchParamNames,
-): string | null => {
-	const urlQuery = useUrlQuery();
-
-	return useMemo(() => {
-		const searchQuery = urlQuery.get(searchParams);
-
-		return searchQuery ? JSON.parse(searchQuery) : null;
-	}, [urlQuery, searchParams]);
-};

frontend/src/hooks/saveViews/__tests__/useGetSavedViewParams.test.ts

@@ -0,0 +1,60 @@
+import { renderHook } from '@testing-library/react';
+import useUrlQuery from 'hooks/useUrlQuery';
+
+import { useGetSavedViewParams } from '../useGetSavedViewParams';
+
+jest.mock('hooks/useUrlQuery');
+
+const mockedUseUrlQuery = useUrlQuery as jest.Mock;
+
+const setSearch = (search: string): void => {
+	mockedUseUrlQuery.mockReturnValue(new URLSearchParams(search));
+};
+
+describe('useGetSavedViewParams', () => {
+	beforeEach(() => {
+		jest.clearAllMocks();
+	});
+
+	it('returns empty strings when no params are present', () => {
+		setSearch('');
+
+		const { result } = renderHook(() => useGetSavedViewParams());
+
+		expect(result.current).toStrictEqual({ viewName: '', viewKey: '' });
+	});
+
+	it('parses JSON-stringified values', () => {
+		setSearch(
+			`viewName=${encodeURIComponent(
+				JSON.stringify('Hindsight'),
+			)}&viewKey=${encodeURIComponent(JSON.stringify('abc-123'))}`,
+		);
+
+		const { result } = renderHook(() => useGetSavedViewParams());
+
+		expect(result.current).toStrictEqual({
+			viewName: 'Hindsight',
+			viewKey: 'abc-123',
+		});
+	});
+
+	it('falls back to the raw string when a value is not valid JSON', () => {
+		setSearch('viewName=Hindsight&viewKey=some-uuid-value');
+
+		const { result } = renderHook(() => useGetSavedViewParams());
+
+		expect(result.current).toStrictEqual({
+			viewName: 'Hindsight',
+			viewKey: 'some-uuid-value',
+		});
+	});
+
+	it('does not throw and keeps the raw string for non-string JSON', () => {
+		setSearch('viewName=123');
+
+		const { result } = renderHook(() => useGetSavedViewParams());
+
+		expect(result.current).toStrictEqual({ viewName: '123', viewKey: '' });
+	});
+});

frontend/src/hooks/saveViews/useGetSavedViewParams.ts

@@ -0,0 +1,33 @@
+import { useMemo } from 'react';
+import { QueryParams } from 'constants/query';
+import useUrlQuery from 'hooks/useUrlQuery';
+
+interface SavedViewParams {
+	viewName: string;
+	viewKey: string;
+}
+
+const parseViewParam = (value: string | null): string => {
+	if (!value) {
+		return '';
+	}
+
+	try {
+		const parsed = JSON.parse(value);
+		return typeof parsed === 'string' ? parsed : value;
+	} catch {
+		return value;
+	}
+};
+
+export const useGetSavedViewParams = (): SavedViewParams => {
+	const urlQuery = useUrlQuery();
+
+	return useMemo(
+		() => ({
+			viewName: parseViewParam(urlQuery.get(QueryParams.viewName)),
+			viewKey: parseViewParam(urlQuery.get(QueryParams.viewKey)),
+		}),
+		[urlQuery],
+	);
+};

frontend/src/hooks/useHandleExplorerTabChange.ts

@@ -6,7 +6,7 @@ import { SIGNOZ_VALUE } from 'container/QueryBuilder/filters/OrderByFilter/const
 import { Query } from 'types/api/queryBuilder/queryBuilderData';
 import { DataSource } from 'types/common/queryBuilder';
 
-import { useGetSearchQueryParam } from './queryBuilder/useGetSearchQueryParam';
+import { useGetSavedViewParams } from './saveViews/useGetSavedViewParams';
 import { useQueryBuilder } from './queryBuilder/useQueryBuilder';
 
 export interface ICurrentQueryData {
@@ -31,9 +31,7 @@ export const useHandleExplorerTabChange = (): {
 		updateQueriesData,
 	} = useQueryBuilder();
 
-	const viewName = useGetSearchQueryParam(QueryParams.viewName) || '';
-
-	const viewKey = useGetSearchQueryParam(QueryParams.viewKey) || '';
+	const { viewName, viewKey } = useGetSavedViewParams();
 
 	const getUpdateQuery = useCallback(
 		(newPanelType: PANEL_TYPES): Query => {

pkg/prometheus/engine.go

@@ -2,6 +2,7 @@ package prometheus
 
 import (
 	"log/slog"
+	"time"
 
 	"github.com/prometheus/prometheus/promql"
 )
@@ -23,5 +24,11 @@ func NewEngine(logger *slog.Logger, cfg Config) *Engine {
 		Timeout:            cfg.Timeout,
 		ActiveQueryTracker: activeQueryTracker,
 		LookbackDelta:      cfg.LookbackDelta,
+		// The engine calls this for subqueries that do not set a step, such as
+		// `metric[5m:]`, and segfaults if it is nil. 1m matches the default
+		// global evaluation_interval that Prometheus wires here.
+		NoStepSubqueryIntervalFn: func(int64) int64 {
+			return time.Minute.Milliseconds()
+		},
 	})
 }

pkg/prometheus/engine_test.go

@@ -0,0 +1,33 @@
+package prometheus
+
+import (
+	"context"
+	"log/slog"
+	"testing"
+	"time"
+
+	"github.com/prometheus/prometheus/storage"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNoStepSubqueryDoesNotPanic(t *testing.T) {
+	engine := NewEngine(slog.New(slog.DiscardHandler), Config{Timeout: time.Minute})
+	queryable := storage.QueryableFunc(func(int64, int64) (storage.Querier, error) {
+		return storage.NoopQuerier(), nil
+	})
+
+	qry, err := engine.NewRangeQuery(
+		context.Background(),
+		queryable,
+		nil,
+		"max_over_time(some_metric[5m:])",
+		time.Now().Add(-time.Hour),
+		time.Now(),
+		time.Minute,
+	)
+	require.NoError(t, err)
+	defer qry.Close()
+
+	res := qry.Exec(context.Background())
+	require.NoError(t, res.Err)
+}

tests/integration/testdata/alerts/test_scenarios/promql_subquery_no_step/alert_data.jsonl

@@ -0,0 +1,5 @@
+{"metric_name":"cpu_percent_promql_subquery_no_step","labels":{"host":"server-01","cpu":"cpu0"},"timestamp":"2026-01-29T10:01:00+00:00","value":15,"temporality":"Unspecified","type_":"Gauge","is_monotonic":false,"flags":0,"description":"","unit":"","env":"default","resource_attrs":{},"scope_attrs":{}}
+{"metric_name":"cpu_percent_promql_subquery_no_step","labels":{"host":"server-01","cpu":"cpu0"},"timestamp":"2026-01-29T10:02:00+00:00","value":15,"temporality":"Unspecified","type_":"Gauge","is_monotonic":false,"flags":0,"description":"","unit":"","env":"default","resource_attrs":{},"scope_attrs":{}}
+{"metric_name":"cpu_percent_promql_subquery_no_step","labels":{"host":"server-01","cpu":"cpu0"},"timestamp":"2026-01-29T10:03:00+00:00","value":15,"temporality":"Unspecified","type_":"Gauge","is_monotonic":false,"flags":0,"description":"","unit":"","env":"default","resource_attrs":{},"scope_attrs":{}}
+{"metric_name":"cpu_percent_promql_subquery_no_step","labels":{"host":"server-01","cpu":"cpu0"},"timestamp":"2026-01-29T10:04:00+00:00","value":15,"temporality":"Unspecified","type_":"Gauge","is_monotonic":false,"flags":0,"description":"","unit":"","env":"default","resource_attrs":{},"scope_attrs":{}}
+{"metric_name":"cpu_percent_promql_subquery_no_step","labels":{"host":"server-01","cpu":"cpu0"},"timestamp":"2026-01-29T10:05:00+00:00","value":15,"temporality":"Unspecified","type_":"Gauge","is_monotonic":false,"flags":0,"description":"","unit":"","env":"default","resource_attrs":{},"scope_attrs":{}}

tests/integration/testdata/alerts/test_scenarios/promql_subquery_no_step/rule.json

@@ -0,0 +1,58 @@
+{
+  "alert": "promql_subquery_no_step",
+  "ruleType": "promql_rule",
+  "alertType": "METRIC_BASED_ALERT",
+  "condition": {
+    "thresholds": {
+      "kind": "basic",
+      "spec": [
+        {
+          "name": "critical",
+          "target": 10,
+          "matchType": "at_least_once",
+          "op": "above",
+          "channels": [
+            "test channel"
+          ]
+        }
+      ]
+    },
+    "compositeQuery": {
+      "queryType": "promql",
+      "panelType": "graph",
+      "queries": [
+        {
+          "type": "promql",
+          "spec": {
+            "name": "A",
+            "query": "max_over_time({\"cpu_percent_promql_subquery_no_step\"}[2m:])"
+          }
+        }
+      ]
+    },
+    "selectedQueryName": "A"
+  },
+  "evaluation": {
+    "kind": "rolling",
+    "spec": {
+      "evalWindow": "5m0s",
+      "frequency": "15s"
+    }
+  },
+  "labels": {},
+  "annotations": {
+    "description": "This alert is fired when the defined metric (current value: {{$value}}) crosses the threshold ({{$threshold}})",
+    "summary": "This alert is fired when the defined metric (current value: {{$value}}) crosses the threshold ({{$threshold}})"
+  },
+  "notificationSettings": {
+    "groupBy": [],
+    "usePolicy": false,
+    "renotify": {
+      "enabled": false,
+      "interval": "30m",
+      "alertStates": []
+    }
+  },
+  "version": "v5",
+  "schemaVersion": "v2alpha1"
+}

tests/integration/tests/alerts/04_promql_subquery_no_step.py

@@ -0,0 +1,93 @@
+import json
+import uuid
+from collections.abc import Callable
+from datetime import UTC, datetime, timedelta
+
+from wiremock.client import HttpMethods, Mapping, MappingRequest, MappingResponse
+
+from fixtures import types
+from fixtures.alerts import (
+    update_rule_channel_name,
+    verify_webhook_alert_expectation,
+)
+from fixtures.fs import get_testdata_file_path
+
+TEST_CASE = types.AlertTestCase(
+    name="promql_subquery_no_step",
+    rule_path="alerts/test_scenarios/promql_subquery_no_step/rule.json",
+    alert_data=[
+        types.AlertData(
+            type="metrics",
+            data_path="alerts/test_scenarios/promql_subquery_no_step/alert_data.jsonl",
+        ),
+    ],
+    alert_expectation=types.AlertExpectation(
+        should_alert=True,
+        wait_time_seconds=30,
+        expected_alerts=[
+            types.FiringAlert(
+                labels={
+                    "alertname": "promql_subquery_no_step",
+                    "threshold.name": "critical",
+                }
+            ),
+        ],
+    ),
+)
+
+
+def test_promql_rule_subquery_without_step(
+    notification_channel: types.TestContainerDocker,
+    make_http_mocks: Callable[[types.TestContainerDocker, list[Mapping]], None],
+    create_webhook_notification_channel: Callable[[str, str, dict, bool], str],
+    create_alert_rule: Callable[[dict], str],
+    insert_alert_data: Callable[[list[types.AlertData], datetime], None],
+):
+    """
+    A promql rule with a step-less subquery ([2m:]) must evaluate and fire.
+    A nil NoStepSubqueryIntervalFn segfaults the process on first evaluation.
+    """
+    notification_channel_name = str(uuid.uuid4())
+    webhook_endpoint_path = f"/alert/{notification_channel_name}"
+    notification_url = notification_channel.container_configs["8080"].get(webhook_endpoint_path)
+
+    make_http_mocks(
+        notification_channel,
+        [
+            Mapping(
+                request=MappingRequest(
+                    method=HttpMethods.POST,
+                    url=webhook_endpoint_path,
+                ),
+                response=MappingResponse(
+                    status=200,
+                    json_body={},
+                ),
+                persistent=False,
+            )
+        ],
+    )
+
+    create_webhook_notification_channel(
+        channel_name=notification_channel_name,
+        webhook_url=notification_url,
+        http_config={},
+        send_resolved=False,
+    )
+
+    insert_alert_data(
+        TEST_CASE.alert_data,
+        base_time=datetime.now(tz=UTC) - timedelta(minutes=5),
+    )
+
+    rule_path = get_testdata_file_path(TEST_CASE.rule_path)
+    with open(rule_path, encoding="utf-8") as f:
+        rule_data = json.loads(f.read())
+    update_rule_channel_name(rule_data, notification_channel_name)
+    create_alert_rule(rule_data)
+
+    verify_webhook_alert_expectation(
+        notification_channel,
+        notification_channel_name,
+        TEST_CASE.alert_expectation,
+    )

tests/integration/tests/promqlconformance/04_no_step_subquery.py

@@ -0,0 +1,65 @@
+from collections.abc import Callable
+from datetime import UTC, datetime, timedelta
+from http import HTTPStatus
+from uuid import uuid4
+
+from fixtures import types
+from fixtures.auth import USER_ADMIN_EMAIL, USER_ADMIN_PASSWORD
+from fixtures.metrics import Metrics
+from fixtures.querier import get_all_series, make_query_request
+
+MINUTE_MS = 60_000
+
+LEGS: list[tuple[str, dict | None]] = [
+    ("default", None),
+    ("clickhousev2", {"X-SigNoz-PromQL-Provider": "clickhousev2"}),
+]
+
+
+def test_promql_subquery_without_step_evaluates(
+    signoz: types.SigNoz,
+    create_user_admin: None,  # pylint: disable=unused-argument
+    get_token: Callable[[str, str], str],
+    insert_metrics: Callable[[list[Metrics]], None],
+) -> None:
+    """
+    A subquery that omits its step, e.g. `metric[5m:]`, is valid PromQL: the
+    engine fills in its default resolution. A nil NoStepSubqueryIntervalFn
+    segfaults the whole process on the first such query.
+    """
+    end_ms = (int((datetime.now(tz=UTC) - timedelta(minutes=5)).timestamp() * 1000) // MINUTE_MS) * MINUTE_MS
+    start_ms = end_ms - 30 * MINUTE_MS
+
+    metric = f"no_step_subquery_gauge_{uuid4().hex[:8]}"
+    insert_metrics(
+        [
+            Metrics(
+                metric_name=metric,
+                labels={"host": "server-01"},
+                timestamp=datetime.fromtimestamp(ts_ms / 1000, tz=UTC),
+                value=42.0,
+            )
+            for ts_ms in range(start_ms, end_ms + 1, MINUTE_MS)
+        ]
+    )
+
+    token = get_token(USER_ADMIN_EMAIL, USER_ADMIN_PASSWORD)
+
+    for leg, headers in LEGS:
+        query = {"type": "promql", "spec": {"name": "A", "query": f"max_over_time({metric}[5m:])"}}
+        response = make_query_request(signoz, token, start_ms, end_ms, [query], headers=headers)
+        assert response.status_code == HTTPStatus.OK, f"{leg}: {response.text[:300]}"
+        series = get_all_series(response.json(), "A")
+        assert series, f"{leg}: the subquery must return the inserted series"
+        values = {point["value"] for entry in series for point in entry.get("values") or []}
+        assert values == {42.0}, f"{leg}: {sorted(values)[:5]}"
+
+    # A plain follow-up query proves the process survived the subquery legs.
+    response = make_query_request(
+        signoz,
+        token,
+        start_ms,
+        end_ms,
+        [{"type": "promql", "spec": {"name": "A", "query": metric}}],
+    )
+    assert response.status_code == HTTPStatus.OK, response.text[:300]