Function participant_display_label 

pub fn participant_display_label(principal: &str) -> String

Turn a durable collaboration principal into copy suitable for people-facing history and audit UI.

Agent principals deliberately remain stored and transported as agent:<id>: the prefix is part of the authorization boundary. Rendering that wire identifier verbatim, however, makes the UI look unfinished and obscures the important fact that the actor was software. This projection removes only the protocol prefix and adds a persistent, readable kind label. Human names and other identifiers pass through unchanged.