The Linux installer ordered its CUDA runtime-line attempts purely by torch's
reported CUDA major (preferred_runtime_line), so a Blackwell host running a
cu12x torch build hoisted cuda12 ahead of an available native cuda13 bundle.
This brings the Linux selector to parity with the existing Windows Blackwell
preference: on an sm_120 host, prefer the highest CUDA-major line that ships
a bundle covering every visible host SM, then fall back to the torch line.
Selection-time only. No external pin and no source build: in-release cuda13
bundles already cover sm_120, and the per-artifact SM filter still drops any
incapable bundle (cuda12-older / cuda13-older) and prevents fall-through to a
non-Blackwell build. The override is gated on _host_is_blackwell and only
reorders lines that are already detected and driver-compatible, so it never
forces cuda13 when its runtime libraries are absent or the driver is pre-13,
and non-Blackwell hosts keep the exact torch-preference behavior.
The runtime-line ranking only considers well-formed "cuda<major>" lines and
skips any malformed or future-format value (e.g. "cuda13.1") instead of
crashing the major sort, matching how the surrounding selector already
tolerates unknown lines.
Adds focused selection tests covering the override, the incapable-cuda13
skip, the cuda13-unavailable fallback, the non-Blackwell no-op, the
malformed-runtime_line skip, and cuda14 forward-compat.
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