Introduce a torch-index MARKER that records the exact wheel --index-url used
after each successful torch install, so `unsloth studio update` / repair makes
the "did the pinned index change?" decision by an EXACT string compare rather
than inferring it from the wheel +rocm/+cu version tag. The tag cannot encode
the AMD per-arch gfx family (two 2.11 gfx indexes both install +rocm7.13.0), so
the tag heuristic missed a gfx1151 -> gfx120X-all switch and a custom-URL swap.
Marker path is per-venv (.unsloth-torch-index), one line = the resolved index
URL, written atomically (temp + rename). Path, format and normalization are
shared across all four installers (install.sh, install_python_stack.py,
setup.ps1, install.ps1).
- Reapply gfx pins on a per-arch target change: the marker's exact compare
reinstalls when the pinned index differs, even when both wheels share a tag.
- Honor custom ROCm URL pins during repair: an explicit index whose leaf is not
rocm/gfx/cu/cpu (e.g. simple, current) now reinstalls torch VERBATIM from the
pin when it differs from the marker ("URL wins verbatim").
- Align the KNOWN-2.11 rocm/gfx set to exactly rocm7.2 plus the gfx allowlist
gfx120x-all/gfx1151/gfx1150 in every language; stop treating an unknown newer
rocm (rocm7.3, which does not exist) as the 2.11 line speculatively.
Backward compatible: with no marker (old venvs, torch installed out-of-band) the
existing +rocm/version-tag heuristics still decide, and a matching marker never
reinstall-loops. A cu128 CUDA pin stays a CUDA pin; custom and current leaves are
not CUDA. Adds marker tests (py/sh/ps) plus cross-installer parity checks.
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