Both said a whole-hive graceful stop costs ONE `GRACEFUL_STOP_TIMEOUT`
in total because drains overlap. That is only true for a power op. In a
rebuild subtree the brace holds the build slot across the whole subtree,
drain included, so the boot sweep's per-agent drains serialise and the
sweep costs one timeout per wave of `buildSlots`.
Deleted rather than corrected. The right cost statement depends on an
operator knob and belongs in docs/coordinator.md if it belongs anywhere;
a comment that has to hedge about a config value is the kind that goes
stale silently. A comment saying nothing beats one that lies.
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