🐛(analytics) filter benign ResizeObserver loop error in Sentry/PostHog

Filter out harmless `ResizeObserver loop limit exceeded` and
`ResizeObserver loop completed with undelivered notifications`
errors via `beforeSend`.

Why this is safe:

* These are W3C spec-mandated browser guards that defer notification
  delivery to the next frame when callbacks alter layout during
  render. They do not cause JS runtime exceptions or break the UX.

Why we actually need to filter them:

* Telemetry platforms like PostHog do not stack/group these well,
  frequently generating distinct error events per browser engine
  and version.
* The unique variants flood reporting dashboards and trigger
  false-positive alerts that clutter real issue triage.

CHANGELOG.md

@@ -20,6 +20,7 @@ and this project adheres to
 - 🐛(frontend) harden speaker test against missing sinks and play errors
 - 🐛(frontend) implement hysteresis band for the control bar layout
 - 🐛(frontend) fix toolbar ResizeObserver loop and alignment drift
+- 🐛(analytics) filter benign ResizeObserver loop error in Sentry/PostHog
 
 ## [1.26.0] - 2026-08-12
 

src/frontend/src/features/analytics/exceptionFilters.ts

@@ -0,0 +1,24 @@
+import type { CaptureResult } from 'posthog-js'
+
+const IGNORED_EXCEPTION_PATTERNS = [
+  /ResizeObserver loop (completed with undelivered notifications|limit exceeded)/,
+]
+
+const shouldIgnoreException = (value: unknown): boolean =>
+  typeof value === 'string' &&
+  IGNORED_EXCEPTION_PATTERNS.some((pattern) => pattern.test(value))
+
+export const filterExceptions = (
+  event: CaptureResult | null
+): CaptureResult | null => {
+  if (event?.event !== '$exception') return event
+
+  const exceptionList = event.properties?.['$exception_list']
+  const values: unknown[] = Array.isArray(exceptionList)
+    ? exceptionList.map((exception) => exception?.value)
+    : []
+
+  values.push(event.properties?.['$exception_message'])
+
+  return values.some(shouldIgnoreException) ? null : event
+}

src/frontend/src/features/analytics/hooks/useAnalytics.ts

@@ -2,6 +2,7 @@ import { useEffect } from 'react'
 import { type ApiUser } from '@/features/auth/api/ApiUser'
 import { useUser } from '@/features/auth/api/useUser'
 import { getPosthog } from '../utils'
+import { filterExceptions } from '../exceptionFilters'
 
 export const startAnalyticsSession = (data: ApiUser) => {
   getPosthog().then((ph) => {
@@ -47,6 +48,7 @@ export const useAnalytics = ({
           capture_unhandled_rejections: true,
           capture_console_errors: true,
         },
+        before_send: filterExceptions,
       })
     })
   }, [id, host, flags_api_host, isDisabled])