v0.3.1 — ask the window manager

AT-SPI cannot say which window is on top: it reports 'active' per application, so several windows claim it at once. 0.3.0 answered that honestly by marking none — which made 'use-computer tree' with no arguments stop on an ordinary desktop to ask something the operating system already knows.

It is not AT-SPI that knows it. On X11 the window manager publishes _NET_ACTIVE_WINDOW, and it is unambiguous. A provider now offers that as a hint and the matching happens above it, so all three platforms share one rule. The refusal does not go away; it stops being the common case.

python-xlib is imported softly and joins the Linux 'tree' extra, which had been empty since BUG-003 for a reason that does not apply to a package with no compiled parts. Absent, or on Wayland, everything behaves as before.

And the 'skill' commands answer in text. 0.3.0 said 'every command, without exception', named two, and missed the one an agent runs to find out whether its own instructions are current.