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".
claude@clouddev1
9868442889