What
The configuration object used when syncing or attaching a session, which already includes things like credentials, allowBundle, and seedDirSync, now also has a firstUpload field pointing to a named handler.
Why
This gives the sync process a dedicated hook to run specifically on the first upload of a session, separate from later uploads.
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubt
The finding does not say what the firstUpload handler actually does.