Function extensions_are_migrated 

pub fn extensions_are_migrated(extensions: &Extensions<GroupContext>) -> bool

Production migration predicate over raw extensions: the group is post-bootstrap iff the AppData dictionary carries the COMPONENT_REGISTRY entry (the bootstrap commit’s first write).

xmtp_mls::groups::app_data::is_migrated_extensions layers a test-only registry override on top of this; use that one inside xmtp_mls. This variant exists for crates below xmtp_mls in the dependency graph (e.g. the archive exporter).