Windows: fix single-AMD-GPU hosts reading as "gpu none" and looping the installer - #8461

…he installer

setup.ps1's WMI fallback built its adapter list with

    $wmiGpus = if ($healthyGpus.Count -gt 0) { $healthyGpus } else { $amdGpus }

An unwrapped one-element branch unrolls to a bare WMI object on its way out of the
if, and a bare WMI object has no .Count in PS 5.1 (a string or hashtable does), so
`if ($wmiGpus.Count -gt 0)` never fired on a host with exactly one AMD adapter and
$ROCmGpuLabel stayed null. Setup reported "gpu none (chat-only / GGUF)", skipped the
name to gfx inference, and the stale-venv check then expected cpu torch against the
ROCm wheels install.ps1 had just placed:

    Stale venv detected (torch rocm != required cpu).
    [ERROR] The existing Unsloth environment needs repair.

The installer rolled back and the desktop app retried the same failure indefinitely.
Reproduced on a Radeon 8060S (gfx1151) Strix Halo laptop, where install.ps1 resolved
gfx1151 and setup.ps1 one second later saw no GPU at all.

Wrap the whole if in @(), the idiom the Intel scan below already documents.

install.ps1 also now exports the arch it resolved before invoking setup.ps1, so the
two never re-derive it independently. Setting UNSLOTH_ROCM_GFX_ARCH by hand was the
workaround for this bug, and doing it in the installer keeps any future divergence
between the two scans from turning into an unrecoverable rollback loop.

…g bug in the name list

Follow-up to the single-AMD-GPU scan fix in this branch, from reviewing what it
could do to hosts other than the one it was reported on.

install.ps1 forwarded its resolved arch as UNSLOTH_ROCM_GFX_ARCH. That name is
the documented operator override, and install_llama_prebuilt.py reads it back as
_manual to decide whether a forwarded --rocm-gfx outranks its own probe, so
publishing an auto-detected value there disarmed that safeguard. install.ps1's
scan is also the weaker of the two: it takes the first AMD adapter with no
visible-device mask and no shadowing-iGPU repick, both of which setup.ps1
applies. On a 780M + RX 9070 XT host setup resolves gfx1201 today; the forward
made it take the installer's gfx1103 verbatim and hand llama.cpp the iGPU
bundle. It was also never restored, so it outlived the install in the caller's
shell on the documented irm | iex path.

It now travels as _UNSLOTH_ROCM_GFX_ARCH_HANDOFF, matching the _UNSLOTH_ prefix
the neighbouring handoffs use, saved and restored in the same finally block, and
consumed by setup.ps1 only after its own probes and inference come up empty.

setup.ps1's gpu name list had the same unwrapped if as the adapter scan: it
wraps each branch but not the if, so a single adapter name unrolls to a bare
String and $gpuNames[$nameIdx] indexes the name and yields "A". The
$nameArches[0] rescue covers that unless a visible-device mask is set, so a
pinned single-GPU host still inferred no arch and looped the same way. Audited
every '= if (' site across the .ps1 files; this was the only other one.

The tests asserted on .Count, which pwsh answers as 1 for a scalar because
PowerShell/PowerShell#5745 added that fallback in 6.1 and Windows PowerShell 5.1
never got it, so they passed against the unfixed source and guarded nothing.
They now assert the shape of the value, re-run each case against stubs carrying
Count = $null to reproduce 5.1's behaviour, cover the mask and multi-adapter
paths and the handoff lifecycle, and pin their own failure against the merge
base.

The check resolved its pre-fix source through git merge-base against main. That
holds only until this merges: after it, the merge base is a commit that already
carries the fix, so the fixed source goes in as the before case and the three
assertions fail on every host with pwsh. Reaching for an older revision at all
also breaks in a shallow CI clone.

It now undoes just the two @() wraps in the shipped source in memory, which is
immutable, needs no git, and isolates the one thing under test since everything
else about the two sources is identical by construction. Verified both ways:
fed the fixed source in as before, the old assertion fails exactly as predicted;
with the wraps undone it reports scalar and no label as it should.

The inference above deliberately leaves $pickedName unset when a mask is set
and the selected adapter's name is not in the table, rather than borrowing a
peer's arch. The handoff then took it anyway: install.ps1 scans without the
masks and forwards the FIRST recognized adapter, so a host masking an unknown
discrete card while a 780M is listed first resolved gfx1103 and installed
wheels and prebuilts for the iGPU the mask hides.

ROCR_VISIBLE_DEVICES filters below HIP, so masked devices never reach the
runtime's enumeration at all, which makes targeting one strictly wrong rather
than merely suboptimal. Setup now skips the handoff whenever any of the three
masks is set, matching what its own inference and Resolve-ShadowingGfxPick
already do. UNSLOTH_ROCM_GFX_ARCH stays the escape hatch and still wins.

Confirmed both ways: with the guard removed the masked host resolves gfx1103,
with it in place it resolves nothing, and the unmasked gap-filling case the
handoff exists for is unchanged.

install.ps1 took the first AMD adapter WMI listed with no health check, while
setup.ps1 filters on ConfigManagerErrorCode. A disabled Radeon listed ahead of a
healthy unsupported one therefore resolved that dead card's arch. Because a
mapped arch installs ROCm wheels right there, the machine got wheels for a GPU
it cannot use while the live card went unserved, and setup, which discards that
adapter, disagreed and took the forwarded arch as its last resort.

Fixed at the source rather than by teaching setup to distrust the handoff:
rejecting it there would leave setup expecting cpu torch against the ROCm wheels
install.ps1 had already placed, which is the stale-venv rollback loop this
branch exists to end. Filtering here means the two scans start from the same
healthy set, so a forwarded arch can only ever name an adapter setup also kept.

Keeps setup's fallback for the case where the filter empties the list, since
code 45 is routine on a muxless laptop with a parked dGPU.

Confirmed both ways: before, the disabled card resolves gfx1201; after, the host
resolves nothing and lands on CPU exactly as setup does.

for more information, see https://pre-commit.ci