Loader stub silently drops calls outside queued method list, which results in either silent no-ops

まず packages/browser-integration-tests/fixtures/loader.js を読み、ロード前のメソッドキューを追跡してから、そのエントリを packages/core/src/integration.ts の addIntegration 実装と比較します。ロード後にキューに入れられた呼び出しがどのように再実行されるかを確認し、選択したガードレールが既存のキュー内メソッドを変更せずに addIntegration を処理することを検証します。

Problem Statement

Problem

The CDN loader stub only queues a fixed set of SDK methods pre-load (init, addBreadcrumb, captureMessage, captureException, captureEvent, configureScope, withScope, showReportDialog). Any SDK call outside this list — such as addIntegration — is silently absent on the window.Sentry proxy before the full bundle loads, causing either silent no-ops or runtime crashes depending on timing.

The correct workaround is wrapping such calls in Sentry.onLoad(...), but the loader provides no mechanism to enforce this, making it easy to write code that works in development (where the bundle may already be loaded) but crashes in production.

Current Behavior

• Unrecognized calls on the pre-load proxy are undefined — calling them throws or silently does nothing
• addIntegration is a notable gap: it is a common post-init call pattern that the loader stub does not queue

Gap

• No TypeScript or runtime guardrail prevents calling unqueued methods before onLoad
• The failure mode is timing-dependent and hard to reproduce locally

Solution Brainstorm

Options

1. Extend the queued method list — add addIntegration (and other commonly used post-init methods) to the pre-load queue so they are replayed after the bundle loads, consistent with how init is handled
2. Catch-all no-op proxy — intercept any unrecognized property access pre-load and return a no-op function; prevents crashes but silently swallows calls
3. Catch-all replay proxy — queue all unrecognized calls (not just the fixed list) and attempt replay post-load; broader coverage but requires more careful handling of methods with return values

Option 1 is the lowest-risk and most targeted fix. Option 3 is the most ergonomic for callers but adds complexity to the replay logic.

Additional Context

References

• Loader stub source: packages/browser-integration-tests/fixtures/loader.js
• addIntegration implementation: packages/core/src/integration.ts

Priority

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