Function format_message_record 

pub fn format_message_record(r: &MessageRecord) -> String

Render one record as HH:MM:SS.mmm <level> <text>. The level prefix lets the reader scan for warns / errors at a glance; the timestamp anchors the entry to wall-clock so users can correlate with logs / external tools.

Phase 5.7.B.9: migrated from lattice-ui-tui::app::messages::format_message_record. pub so subsystem crates (drain loops, test fixtures) can reach the canonical format.