fix(sdk): drop unhandled rejection noise from browser extensions in beforeSend

[billyvg]

Drop UnhandledRejection events that originate from browser extensions (MetaMask, other crypto-wallet content scripts) — they are third-party noise, never actionable by Sentry engineers.

Problem

Browser extensions like MetaMask fire their own unhandled promise rejections (e.g. error code 4001 — "MetaMask Personal Sign: User denied message signature") into the host page's global unhandledrejection handler. The Sentry SDK captures these and reports them as real issues.

The thirdPartyErrorFilterIntegration is configured with behaviour: 'apply-tag-if-contains-third-party-frames', which only tags events — it does not drop them. So these extension events make it all the way to Sentry.

Characteristics of the noise:

• mechanism.type === 'auto.browser.global_handlers.onunhandledrejection'
• originalException is a plain object (not an Error) with a .stack property pointing at chrome-extension:// or moz-extension://
• No frames from Sentry's own code; entirely third-party

Fix

Add isBrowserExtensionError(event, hint) and call it in beforeSend. It returns true (→ null → dropped) when:

1. The exception mechanism is onunhandledrejection
2. hint.originalException is a non-Error plain object with a .stack string containing chrome-extension:// or moz-extension://

This is intentionally narrow: it only drops events where the original rejection value itself points at an extension, not events where an extension merely appears somewhere in the stack of a real Error.

Evidence

Triggered by an alert for event 0a22da40441f40ba85512dfdf107649b on the /explore/traces/ page. Full stack trace was:

Error: MetaMask Personal Sign: User denied message signature.
  at chrome-extension://acmacodkjbdgmoleebolmdjonilkdbch/content-script.js

No Sentry frames. The rejection value was {code: 4001, message: "...", stack: "...chrome-extension://..."} — a plain object, not an Error.

Session

https://claude.ai/code/session_015Gd856MCZWtWz8VmqLdaA3

Legal Boilerplate

Look, I get it. The entity doing business as "Sentry" was incorporated in the State of Delaware in 2015 as Functional Software, Inc. and is gonna need some rights from me in order to utilize my contributions in this here PR. So here's the deal: I retain all rights, title and interest in and to my contributions, and by keeping this boilerplate intact I confirm that Sentry can use, modify, copy, and redistribute my contributions, under Sentry's choice of terms.

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Generated by Claude Code

[github-actions]

📊 Type Coverage Diff

Metric	Before	After	Delta
Coverage	93.93%	93.93%	±0%
Typed	134,708	134,754	🟢 +46
Untyped	8,704	8,707	🔴 +3

🔍 3 new type safety issues introduced

Non-null assertions (!) (1 new)

File	Line	Detail
static/app/components/searchQueryBuilder/askSeerCombobox/humanizedToEsq.ts	57	words[i]!

Type assertions (as) (2 new)

File	Line	Detail
static/app/bootstrap/initializeSdk.tsx	296	as Record<string, unknown> — originalException as Record<string, unknown>
static/app/bootstrap/initializeSdk.tsx	298	as {stack: string} — originalException as {stack: string}

This is informational only and does not block the PR.