Invite multiple people through e-groups

Manually adding multiple participants can be arduous, especially for a group activity that could generally be solved by inviting all the participants of an e-group. This issue suggests the implementation of multipass (or local) group based participants.

Start by reading the issue body and locating the existing manual participant invitation flow. Determine how multipass or local e-group participants should be represented and what completion behavior is required; the issue names no files or tests, so acceptance criteria need clarification before implementation.

Written by the indexing model from the issue text.