The progressive-depth help engine that discovers features, generates depth-layered templates, and serves contextual help

Notes & tips

• Import from the owning submodule (no top-level __all__), or use the help.engine facade for the contextual/feedback helpers.
• Counts are properties. stale_features, stale_count, regenerated_count, current_count — no ().
• populate is nullable. Always check for None.
• Maintenance is hash-based. It only regenerates features whose source actually changed; dry_run=True reports without writing.