Verified on blueline that Hyprland advertises primary-selection plus both
data-control managers, so wl-paste --primary --watch sees every selection with
no per-app hooks. Settles TASK-18's selection-detection question as
compositor-level; viewtop is not needed.
The protocol gives no selection rectangle, so anchor is the pointer position at
selection time. Opt-in by default: the watcher observes every highlight on the
device, including passwords, so it is killed while locked and selection text is
never persisted, logged, or trailed.
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