docs: clarify array attributes impact on beforeSend callbacks

Move the array attributes entry to the top of the 10.54.0 Important
Changes section and explicitly call out that beforeSend* callbacks
assuming primitive attribute values need to be updated.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: nicohrubec

CHANGELOG.md

@@ -20,6 +20,10 @@
 
 ### Important Changes
 
+- **feat(core): Support array attributes for spans, logs, and metrics ([#20427](https://github.com/getsentry/sentry-javascript/pull/20427))**
+
+  Arrays of primitive values (`string`, `number`, `boolean`) are now accepted as attribute values. Arrays containing non-primitive elements will be dropped. Array attributes on logs and metrics were previously stringified and will now be sent as actual arrays instead. **If you use `beforeSend*` callbacks that assume attribute values are always primitive (e.g., `typeof value === 'string'`), update them to handle array values as well.**
+
 - **feat(browser): Add `fetchStreamPerformanceIntegration` for streamed response tracking ([#20778](https://github.com/getsentry/sentry-javascript/pull/20778))**
 
   A new integration that tracks the performance of streamed fetch responses. Use this to measure time-to-first-byte and streaming duration for APIs that return chunked/streamed data. This replaces the now deprecated `trackFetchStreamPerformance` option.
@@ -28,10 +32,6 @@
 
   Adds a new `dataCollection` client option for controlling what data the SDK collects and sends to Sentry. This provides a centralized way to configure data collection behavior across different SDK features. In the future, this option will be used for fine-granular data filtering, while the simple `sendDefaultPii` boolean option will be deprecated and removed in a future release.
 
-- **feat(core): Support array attributes for spans, logs, and metrics ([#20427](https://github.com/getsentry/sentry-javascript/pull/20427))**
-
-  Arrays of primitive values (`string`, `number`, `boolean`) are now accepted as attribute values. Arrays containing non-primitive elements will be dropped and won't show up in Sentry. Note that array attributes on logs and metrics were previously stringified in certain cases and will now be sent as arrays instead.
-
 - **feat(hono): Add `hono.request` spans for internal `.request()` calls ([#20843](https://github.com/getsentry/sentry-javascript/pull/20843))**
 
   The Hono SDK now creates spans for internal `.request()` calls, providing better visibility into request handling within Hono applications.