Run each child with its own files and loop

Run each child with its own files and loop

The daemon opens the root and each direct child with separate memory,
compaction, usage records, schedules, and subagents. Invalid child
configuration stops startup, and the ready event names the children.
Each child uses its own cache key and has no WhatsApp tools. Its turn
and compaction calls share the same prompt and tools.

Backups flush and lock every agent and its subagent logs during the
copy, so the archive holds the full state of the children as well as the
root. Clients still address only the root.