record_step appends to walked_path JSONB and advances current_node_id
on flow/proposal walks; refuses adhoc sessions. update_notes replaces
walk_notes (used by adhoc walks for debounced autosave); 256KB size cap
to prevent unbounded JSONB growth. Both reject non-active sessions.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>