beforeErrorSampling does not respect sampling based on event level

[InterstellarStella]

Is there an existing issue for this?

• I have checked for existing issues https://github.com/getsentry/sentry-javascript/issues
• I have reviewed the documentation https://docs.sentry.io/
• I am using the latest SDK release https://github.com/getsentry/sentry-javascript/releases

How do you use Sentry?

Sentry Saas (sentry.io)

Which SDK are you using?

@sentry/react

SDK Version

"@sentry/react": "^9.46.0"

Framework Version

"react": "^19.1.0"

Link to Sentry event

https://dragonfruit-us.sentry.io/issues/6928059664/?project=4504179109068800&query=is%3Aunresolved&referrer=issue-stream

Reproduction Example/SDK Setup

In instrument.js:

// ...
Sentry.replayIntegration({
      beforeErrorSampling: (event) => {
        console.log("beforeErrorSampling", event);
        if (event.level === "error") {
          console.log("Capturing replay for error");
          return event;
        }
        console.log("Not capturing replay because level is not error");
        return null;
      },
    }),
// ...
replaysSessionSampleRate: 0.0,
replaysOnErrorSampleRate: 1.0,

In App.jsx:

 <button
          type="button"
          onClick={() => {
            Sentry.withScope(function (scope) {
              scope.setLevel("info");
              // The exception has the event level set by the scope (info).
              Sentry.captureException(new Error("custom error"));
            });
          }}
        >
          Send info
        </button>

Steps to Reproduce

1. Set up a beforeErrorSampling that decides when a replay should be recorded based on the event level, making sure that the replay session sampling rate is 0
2. Using the scope, change the event level to one that should not send a replay to Sentry based on your logic
3. Trigger an event that should not have a replay attached to it

Expected Result

The event arrives in Sentry without a replay.

Actual Result

The event arrives in Sentry with a replay.
The above is a reproduction from my test app and org. Original customer ticket here.

Additional Context

_{Tip: React with 👍 to help prioritize this issue. Please use comments to provide useful context, avoiding +1 or me too, to help us triage it.}

[linear]

JS-1025

[logaretm]

Thanks for the description, I spent some time attempting to reproduce this with the given info across the latest SDK release 10.18.0 and the one reported 9.48.0 and didn't manage to reproduce it.

I assume this may happen if the replay is in session mode rather than buffer mode, since beforeErrorSampling only affects the sampling decision in buffer mode and has no effect otherwise which is intended behavior at the moment.

This might be confusing because once a replay is captured in buffer mode due to an error, it will continue recording in session mode which is intentional since we want to capture what happened after the error.

There is a similar discussion in #15470. I think we can document this better, also I will try to see if there is a bug with sticky session variable persistence since it may add to the confusion.