HIVE_PRIV_EXE, set by the module to the /run/hive-rootfs-check link, is
checked at start and used for the drop-in's ExecStartPre. Without it the
running binary's path is used as before, and an unlinked one gets an
error that names the cause.
The hive dashboard and the per-agent page lose their control-by-control UI
description and endpoint tables from the handbook. The full text moves to
4-implementation/web-ui/dashboard.md and agent-page.md, and the handbook pages
keep what an operator needs to find and use them. Code comments that named the
old sections point at the new pages.
The operator parts of the persistence and config-changes pages merge into
agents/persistence.md. The sqlite tables, state dirs, mounts and migrations move
to 4-implementation/agent-state/persistence.md, and the deploy path, meta flake,
deploy markers, startup migrations, root container, system messages and
autoupdate move to 4-implementation/agent-state/config-changes.md. Links, code
comments and nix comments that named the old sections point at the new pages.
