It would be good to know how compression works etc. for replay events. There are a few cases:

• Compression is turned off via useCompression: false
• Compression is enabled and used
• Compression is enabled but we fall back to uncompressed mode due to e.g. worker loading issues

I propose to add a field compressionMode to the replay event payload:

type CompressionMode = 'disabled' | 'compressed' | 'fallback';

type ReplayEvent {
 // ... existing fields
  compressionMode: CompressionMode
}

This way, we can later run analysis how frequently compression fails, which can inform decisions about the compression strategy etc.

We can also eventually use this information to give users tips for improving their replay setup - if we detect a project has only events with fallback compression mode, we can prompt the user to either fix their CSP settings or disable compression, as an example.