The windows-tests merge made tests.yml a 3-OS matrix with the FULL
suite on Windows (pytest-xdist loadfile) — whose worker-crash flake
(INTERNALERROR on a random file every run) has been red-flagging the
branch. Per ethie: don't rip the windows-tests merge's test fixes, just
match upstream/main's CI shape. tests.yml is back to the Linux-only
96-core full-suite lane (per-file subprocess isolation); tests-os.yml
restored for the macOS/Windows marked-test lanes (plain pytest, small
set, no xdist — adapted 2 our platforms() marker convention with
'-m platforms and not integration'); ci.yaml wires tests-os back with
its desktop_updater input gate + all-checks-pass dependency.
95eba6d940