fix(sentry): drop benign closed-channel postMessage error on client

sentry.client.config.ts

@@ -1,5 +1,5 @@
 import * as Sentry from '@sentry/nuxt'
-import { createSentryDataCollection, isLocalReportingHost, SENTRY_DSN } from './shared/sentry'
+import { createSentryDataCollection, isClosedBroadcastChannelError, isLocalReportingHost, SENTRY_DSN } from './shared/sentry'
 
 if (!import.meta.dev && window.location.protocol === 'https:' && !isLocalReportingHost(window.location.hostname)) {
   // No `release` here on purpose. The Sentry bundler plugin injects the release
@@ -19,5 +19,15 @@ if (!import.meta.dev && window.location.protocol === 'https:' && !isLocalReporti
       /Importing a module script failed/i,
       /error loading dynamically imported module/i,
     ],
+    // nuxt-skew-protection's multi-tab plugin closes its BroadcastChannel on
+    // app:error, and an in-flight version update can still post to it. The
+    // rejection is a benign tab-close race (SKILLD-12), so drop that one
+    // signature and keep every other error.
+    beforeSend(event, hint) {
+      const values = event.exception?.values ?? []
+      if (isClosedBroadcastChannelError(hint.originalException) || values.some(isClosedBroadcastChannelError))
+        return null
+      return event
+    },
   })
 }

shared/sentry.ts

@@ -86,6 +86,20 @@ export function isExpectedUpstreamOutageError(error: unknown): boolean {
   return typeof message === 'string' && message.endsWith('unavailable upstream')
 }
 
+/**
+ * The message Chrome rejects a `postMessage` on a closed `BroadcastChannel`
+ * with (`InvalidStateError`, Sentry SKILLD-12). nuxt-skew-protection's
+ * multi-tab plugin closes its channel on `app:error`, and a version update
+ * already in flight can still post to it. The tab is erroring or closing
+ * anyway, and the other tabs pick the version up on their own poll, so the
+ * rejection is benign. The client Sentry config drops exactly that signature
+ * in `beforeSend`; a closed-channel post on any other target still lands.
+ */
+export function isClosedBroadcastChannelError(error: unknown): boolean {
+  const message = sentryExceptionMessage(error)
+  return message === 'Failed to execute \'postMessage\' on \'BroadcastChannel\': Channel is closed'
+}
+
 export function createSentryDataCollection() {
   return {
     userInfo: false,

test/unit/sentry-cache-write-filter.test.ts

@@ -1,5 +1,36 @@
 import { beforeEach, describe, expect, it, vi } from 'vitest'
-import { isBestEffortCacheWriteError, isExpectedUpstreamOutageError } from '../../shared/sentry'
+import { isBestEffortCacheWriteError, isClosedBroadcastChannelError, isExpectedUpstreamOutageError } from '../../shared/sentry'
+
+describe('isClosedBroadcastChannelError', () => {
+  const closed = 'Failed to execute \'postMessage\' on \'BroadcastChannel\': Channel is closed'
+
+  it('matches the SKILLD-12 closed-channel postMessage the multi-tab plugin throws', () => {
+    expect(isClosedBroadcastChannelError(new DOMException(closed, 'InvalidStateError'))).toBe(true)
+  })
+
+  it('matches the Sentry-serialized exception, whose message arrives as value', () => {
+    expect(isClosedBroadcastChannelError({
+      type: 'InvalidStateError',
+      value: closed,
+      mechanism: { handled: false, type: 'auto.browser.global_handlers.onunhandledrejection' },
+    })).toBe(true)
+  })
+
+  it('ignores postMessage failures on other targets, which are not the tab-close race', () => {
+    expect(isClosedBroadcastChannelError(
+      new DOMException('Failed to execute \'postMessage\' on \'Worker\': Channel is closed', 'InvalidStateError'),
+    )).toBe(false)
+    expect(isClosedBroadcastChannelError(
+      new DOMException('Failed to execute \'postMessage\' on \'BroadcastChannel\': An object could not be cloned.', 'DataCloneError'),
+    )).toBe(false)
+  })
+
+  it('ignores generic invalid-state errors and values that are not errors', () => {
+    expect(isClosedBroadcastChannelError(new DOMException('The object is in an invalid state.', 'InvalidStateError'))).toBe(false)
+    expect(isClosedBroadcastChannelError(closed)).toBe(false)
+    expect(isClosedBroadcastChannelError(undefined)).toBe(false)
+  })
+})
 
 describe('isBestEffortCacheWriteError', () => {
   it('matches the SKILLD-17 rate-limited KV write signature', () => {