fix: Infer singular quantileXxxMerge() from MV quantilesXxxState() (#2154)

## Summary

This PR fixes a bug in the quantile function inference used for MV queries. For MVs defined with `quantilesXxxState()` columns, HyperDX will now infer a `quantileXxxMerge` function instead of a `quantilesXxxMerge` function. `quantilesXxxMerge` returns an array result, which is incompatible with HyperDX's chart implementations.

I've tested that quantile, quantileTDigest, and quantileExact all return equivalent results when querying `quantileXxxMerge` and `quantilesXxxMerge` from a `quantilesXxxState` column.

### Screenshots or video

Before:

<img width="1021" height="554" alt="Screenshot 2026-04-23 at 7 47 59 AM" src="https://github.com/user-attachments/assets/4cb325a9-be69-404b-8975-4d2066aee6c1" />

After:

<img width="1023" height="740" alt="Screenshot 2026-04-23 at 7 47 33 AM" src="https://github.com/user-attachments/assets/ca7ca7a0-d0be-4857-9f6c-fba1c25bd2c9" />


### How to test locally or on Vercel

This can be tested locally by creating a MV as follows and registering it in the Traces source configuration:

```sql
CREATE TABLE otel_traces_1m_quantiles
(
    `Timestamp` DateTime,
    `ServiceName` LowCardinality(String),
    `StatusCode` LowCardinality(String),
    `count` SimpleAggregateFunction(sum, UInt64),
    `avg__Duration` AggregateFunction(avg, UInt64),
    `max__Duration` SimpleAggregateFunction(max, Int64),
    `quantiles__Duration` AggregateFunction(quantiles(0.5, 0.95), UInt64)
)
ENGINE = AggregatingMergeTree
ORDER BY (Timestamp, ServiceName, StatusCode);

CREATE MATERIALIZED VIEW otel_traces_1m_quantiles_mv TO otel_traces_1m_quantiles
AS
SELECT
    toStartOfMinute(Timestamp) AS Timestamp,
    ServiceName,
    StatusCode,
    count() AS count,
    avgState(Duration) AS avg__Duration,
    maxSimpleState(Duration) AS max__Duration,
    quantilesState(0.5, 0.95)(Duration) AS quantiles__Duration
FROM otel_traces
GROUP BY
    Timestamp,
    ServiceName,
    StatusCode;
```

### References



- Linear Issue: Closes HDX-4099 Closes #2153 
- Related PRs:

Author: pulpdrew

.changeset/cool-students-camp.md

@@ -0,0 +1,6 @@
+---
+"@hyperdx/common-utils": patch
+"@hyperdx/app": patch
+---
+
+fix: Infer singular quantileXXX() from MV quantilesXXXState()

packages/common-utils/src/clickhouse/__tests__/materializedViews.test.ts

@@ -287,6 +287,112 @@ describe('materializedViews', () => {
       expect(result.errors).toBeUndefined();
     });
 
+    it('should normalize a quantiles AggregateFunction to quantileMerge', async () => {
+      const quantilesMetadata: Metadata = {
+        getColumn: jest.fn().mockImplementation(({ column }) => {
+          if (column === 'quantile__Duration') {
+            return {
+              type: 'AggregateFunction(quantiles(0.9, 0.95), UInt64)',
+            } as unknown as ColumnMeta;
+          }
+          return undefined;
+        }),
+      } as unknown as Metadata;
+
+      const chartConfig: ChartConfigWithOptDateRange = {
+        from: {
+          databaseName: 'default',
+          tableName: 'otel_spans',
+        },
+        select: [
+          {
+            valueExpression: 'Duration',
+            aggFn: 'quantile',
+            level: 0.95,
+          },
+        ],
+        where: '',
+        connection: 'test-connection',
+      };
+
+      const result = await tryConvertConfigToMaterializedViewSelect(
+        chartConfig,
+        MV_CONFIG_METRIC_ROLLUP_1M,
+        quantilesMetadata,
+      );
+
+      expect(result.optimizedConfig).toEqual({
+        from: {
+          databaseName: 'default',
+          tableName: 'metrics_rollup_1m',
+        },
+        select: [
+          {
+            valueExpression: 'quantile__Duration',
+            aggFn: 'quantileMerge',
+            level: 0.95,
+          },
+        ],
+        timestampValueExpression: 'Timestamp',
+        where: '',
+        connection: 'test-connection',
+      });
+      expect(result.errors).toBeUndefined();
+    });
+
+    it('should normalize a quantilesTDigest AggregateFunction to quantileTDigestMerge', async () => {
+      const quantilesTDigestMetadata: Metadata = {
+        getColumn: jest.fn().mockImplementation(({ column }) => {
+          if (column === 'quantile__Duration') {
+            return {
+              type: 'AggregateFunction(quantilesTDigest(0.9, 0.95), UInt64)',
+            } as unknown as ColumnMeta;
+          }
+          return undefined;
+        }),
+      } as unknown as Metadata;
+
+      const chartConfig: ChartConfigWithOptDateRange = {
+        from: {
+          databaseName: 'default',
+          tableName: 'otel_spans',
+        },
+        select: [
+          {
+            valueExpression: 'Duration',
+            aggFn: 'quantile',
+            level: 0.95,
+          },
+        ],
+        where: '',
+        connection: 'test-connection',
+      };
+
+      const result = await tryConvertConfigToMaterializedViewSelect(
+        chartConfig,
+        MV_CONFIG_METRIC_ROLLUP_1M,
+        quantilesTDigestMetadata,
+      );
+
+      expect(result.optimizedConfig).toEqual({
+        from: {
+          databaseName: 'default',
+          tableName: 'metrics_rollup_1m',
+        },
+        select: [
+          {
+            valueExpression: 'quantile__Duration',
+            aggFn: 'quantileTDigestMerge',
+            level: 0.95,
+          },
+        ],
+        timestampValueExpression: 'Timestamp',
+        where: '',
+        connection: 'test-connection',
+      });
+      expect(result.errors).toBeUndefined();
+    });
+
     it('should convert a histogram AggregateFunction select', async () => {
       const chartConfig: ChartConfigWithOptDateRange = {
         from: {

packages/common-utils/src/core/materializedViews.ts

@@ -65,11 +65,15 @@ async function getQuantileAggregateFunction(
     }
 
     // Use regex to extract the quantile function name inside AggregateFunction(...)
-    // For example, AggregateFunction(quantile(0.95), Int64) --> quantile
+    // For example, AggregateFunction(quantile(0.95), Int64)       --> quantile
     //              AggregateFunction(quantileTDigest(0.95), Int64) --> quantileTDigest
     //              AggregateFunction(quantileDD(0.001, 0.95), Int64) --> quantileDD
+    // The plural `quantiles*` variants return arrays, but a select item carries a
+    // single `level`, so we normalize to the singular form to pull a scalar value.
+    //              AggregateFunction(quantiles(0.9, 0.95), UInt64)        --> quantile
+    //              AggregateFunction(quantilesTDigest(0.9, 0.95), UInt64) --> quantileTDigest
     const match = type.match(/^AggregateFunction\(\s*([^(, ]+)\s*\(/);
-    return match?.[1];
+    return match?.[1]?.replace(/^quantiles/, 'quantile');
   } catch {
     return undefined;
   }