_manual_compress_turn's CompressionBusy is the only busy gate on
session.compress (its pre-check was removed), and it still built the
"Hermes is still replying. Stop..." text. A second session.compress during
a manual compaction (Desktop double-click) told the user to press Stop,
which does not end a compaction. Pass the _manual_compress_active marker to
busy_message like every other refusal site already does.
Finding: [Low BUG-IN-NEW-CODE] C04 quality r4 (fold3 missed this caller).