- Move cache_control from request root (ignored by API) to per-block
placement on last system block and last tool definition
- Change system prompt time format to date-only for better cache stability
- Add builtin datetime tool for precise timestamps (cron, memory, etc.)
- Add atMs past-time validation in cron handleUpdate (was only in handleAdd)
- Update cron description to guide model to use datetime tool first
viettranx