9868442889
Phased build plan: mechanism skeleton with tier-2 fallback first (hint_id field, AppCommand::Hint, F1 read-only overlay, last_error_hint_key, note_hint* renderer), then catalogue + the three approved exemplars, then comprehensive content in batches, then polish. Reuses the existing command_for_entry_word / usage_keys_for_input_in_mode lookups for command identification. Test spine includes the comprehensiveness coverage test that gates "comprehensive for v1".