fix: drop screenshots for events filtered by before_send

[JoshuaMoelans]

Fixes #2641

Since screenshots await EndOfFrame() , we start a coroutine that ends up sending an envelope with just the screenshot item. However, in the meantime, the related event might have been discarded by the before_send filter. In this case, we don't want to send unnecessary data over to Relay.

As a temporary workaround, setting SetBeforeCaptureScreenshot to the same filter used in SetBeforeSend prevents these screenshots from being sent.

Proposed Fix

• Add internal bool WasCaptured to SentryEvent (sentry-dotnet/SentryEvent.cs:249) — a flag that tracks whether an event actually made it through the entire send pipeline. Defaults to false, which is the safe default: if the flag is never set, the screenshot is skipped rather than sent as an orphan.

• Set it to true on the success path in DoSendEvent (sentry-dotnet/SentryClient.cs:416) — placed immediately after CaptureEnvelope returns true, which is the only point where we know the event was actually sent. The flag is set on the original @event parameter (not processedEvent) because event processors and before_send can swap the event object, but the screenshot coroutine's closure holds a reference to the original. All five drop paths (exception filters, event processors, before_send, sampling, transport failure) return early and never reach this line, leaving the flag false.

• Check the flag in the screenshot coroutine before capturing (ScreenshotEventProcessor.cs:48) — after WaitForEndOfFrame resumes the coroutine (at which point DoSendEvent has already completed synchronously), we read WasCaptured. If false, we yield break and skip the screenshot entirely. This check runs before any screenshot capture or CaptureAttachment call, preventing orphaned attachment envelopes from ever being created.

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Related PRs:

• fix: Screenshot Capture #2240
• feat: Added internal bool CaptureAttachment to Hub sentry-dotnet#4357

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Semver Impact of This PR

🟢 Patch (bug fixes)

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Bug Fixes 🐛

• Drop screenshots for events filtered by before_send by JoshuaMoelans in #2642

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