fix(aci): use aggregate output type for % change detection charts (#104061)

fixes an issue where percent change metrics were displaying the yAxis as
a percentage when we want the actual count/seconds etc

<img width="576" height="215" alt="image"
src="https://github.com/user-attachments/assets/8238ba08-f572-428a-8917-8beab169ba8f"
/>

Author: scttcper

static/app/views/detectors/utils/detectorChartFormatting.spec.tsx

@@ -23,14 +23,27 @@ describe('getDetectorChartFormatters', () => {
     expect(result.formatTooltipValue(2000)).toBe('2.00s');
   });
 
-  it('percent detection: returns percentage type and % suffix', () => {
+  it('percent detection: uses aggregate output type and does not append % to formatters', () => {
     const result = getDetectorChartFormatters({
       detectionType: 'percent',
       aggregate: 'count()',
     });
 
-    expect(result.outputType).toBe('percentage');
+    // % change detection should use the aggregate's actual type (number), not percentage
+    expect(result.outputType).toBe('number');
+    // unitSuffix is still % for threshold display purposes
     expect(result.unitSuffix).toBe('%');
-    expect(result.formatTooltipValue(0.25)).toBe('25%');
+    // But formatters should NOT append % since primary series shows actual metric values
+    expect(result.formatTooltipValue(1000)).toBe('1,000');
+    expect(result.formatYAxisLabel(1000)).toBe('1k');
+  });
+
+  it('percentage aggregate (crash_free_rate): returns percentage type', () => {
+    const result = getDetectorChartFormatters({
+      detectionType: 'static',
+      aggregate: 'crash_free_rate(session)',
+    });
+
+    expect(result.outputType).toBe('percentage');
   });
 });

static/app/views/detectors/utils/detectorChartFormatting.tsx

@@ -17,22 +17,22 @@ export function getDetectorChartFormatters({
   detectionType,
   aggregate,
 }: DetectorChartFormatterOptions) {
-  const outputType =
-    detectionType === 'percent' ? 'percentage' : aggregateOutputType(aggregate);
+  const outputType = aggregateOutputType(aggregate);
   const unitSuffix = getMetricDetectorSuffix(detectionType, aggregate);
 
+  // For % change detection, the primary series shows actual metric values (counts, durations, etc.)
+  // The % suffix is only for threshold display, not for y-axis/tooltip formatting
+  const shouldAppendSuffix =
+    detectionType !== 'percent' && (outputType === 'number' || outputType === 'integer');
+
   const formatYAxisLabel = (value: number): string => {
     const base = axisLabelFormatterUsingAggregateOutputType(value, outputType, true);
-    return outputType === 'number' || outputType === 'integer'
-      ? `${base}${unitSuffix}`
-      : base;
+    return shouldAppendSuffix ? `${base}${unitSuffix}` : base;
   };
 
   const formatTooltipValue = (value: number): string => {
     const base = tooltipFormatterUsingAggregateOutputType(value, outputType);
-    return outputType === 'number' || outputType === 'integer'
-      ? `${base}${unitSuffix}`
-      : base;
+    return shouldAppendSuffix ? `${base}${unitSuffix}` : base;
   };
 
   return {