fix(browser): Ignore React 19.2+ component render measure entries (#1…

…7905)

With 19.2, React introduced [custom perfomance
tracks](https://react.dev/blog/2025/10/01/react-19-2#performance-tracks)
in chrome dev tools. This track is populated by collecting
`performance.measure` entries for every component (re-)render. Sounds
good in theory but in reality this causes a massive performance
degradation when using the Sentry SDK because we collect spans from
`PerformanceMeasure` entries. In our Sentry UI, this caused 10+ second
long blocks because we created thousands of spans from these render
entries.

This patch fixes this performance drop by inspecting the measure entries'
`detail` object which we can use to _fairly well_ distinguish React's
entries from users' entries. Not 100% bulletproof but I think good
enough.

packages/browser-utils/src/metrics/browserMetrics.ts

@@ -425,6 +425,24 @@ export function addPerformanceEntries(span: Span, options: AddPerformanceEntries
   _measurements = {};
 }
 
+/**
+ * React 19.2+ creates performance.measure entries for component renders.
+ * We can identify them by the `detail.devtools.track` property being set to 'Components ⚛'.
+ * see: https://react.dev/reference/dev-tools/react-performance-tracks
+ * see: https://github.com/facebook/react/blob/06fcc8f380c6a905c7bc18d94453f623cf8cbc81/packages/react-reconciler/src/ReactFiberPerformanceTrack.js#L454-L473
+ */
+function isReact19MeasureEntry(entry: PerformanceEntry | null): boolean | void {
+  if (entry?.entryType !== 'measure') {
+    return;
+  }
+  try {
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-member-access
+    return (entry as PerformanceMeasure).detail.devtools.track === 'Components ⚛';
+  } catch {
+    return;
+  }
+}
+
 /**
  * Create measure related spans.
  * Exported only for tests.
@@ -437,6 +455,10 @@ export function _addMeasureSpans(
   timeOrigin: number,
   ignorePerformanceApiSpans: AddPerformanceEntriesOptions['ignorePerformanceApiSpans'],
 ): void {
+  if (isReact19MeasureEntry(entry)) {
+    return;
+  }
+
   if (
     ['mark', 'measure'].includes(entry.entryType) &&
     stringMatchesSomePattern(entry.name, ignorePerformanceApiSpans)
@@ -445,6 +467,7 @@ export function _addMeasureSpans(
   }
 
   const navEntry = getNavigationEntry(false);
+
   const requestTime = msToSec(navEntry ? navEntry.requestStart : 0);
   // Because performance.measure accepts arbitrary timestamps it can produce
   // spans that happen before the browser even makes a request for the page.

packages/browser-utils/test/browser/browserMetrics.test.ts

@@ -186,6 +186,75 @@ describe('_addMeasureSpans', () => {
       ]),
     );
   });
+
+  it('ignores React 19.2+ measure spans', () => {
+    const pageloadSpan = new SentrySpan({ op: 'pageload', name: '/', sampled: true });
+    const spans: Span[] = [];
+
+    getClient()?.on('spanEnd', span => {
+      spans.push(span);
+    });
+
+    const entries: PerformanceMeasure[] = [
+      {
+        entryType: 'measure',
+        name: '\u200bLayout',
+        duration: 0.3,
+        startTime: 12,
+        detail: {
+          devtools: {
+            track: 'Components ⚛',
+          },
+        },
+        toJSON: () => ({ foo: 'bar' }),
+      },
+      {
+        entryType: 'measure',
+        name: '\u200bButton',
+        duration: 0.1,
+        startTime: 13,
+        detail: {
+          devtools: {
+            track: 'Components ⚛',
+          },
+        },
+        toJSON: () => ({}),
+      },
+      {
+        entryType: 'measure',
+        name: 'Unmount',
+        duration: 0.1,
+        startTime: 14,
+        detail: {
+          devtools: {
+            track: 'Components ⚛',
+          },
+        },
+        toJSON: () => ({}),
+      },
+      {
+        entryType: 'measure',
+        name: 'my-measurement',
+        duration: 0,
+        startTime: 12,
+        detail: null,
+        toJSON: () => ({}),
+      },
+    ];
+
+    const timeOrigin = 100;
+    const startTime = 23;
+    const duration = 356;
+
+    entries.forEach(e => {
+      _addMeasureSpans(pageloadSpan, e, startTime, duration, timeOrigin, []);
+    });
+
+    expect(spans).toHaveLength(1);
+    expect(spans.map(spanToJSON)).toEqual(
+      expect.arrayContaining([expect.objectContaining({ description: 'my-measurement', op: 'measure' })]),
+    );
+  });
 });
 
 describe('_addResourceSpans', () => {