install: make the torch-index override authoritative across ROCm paths

Address review feedback on the override added in this PR so a pinned index is
honoured everywhere, not just in get_torch_index_url:

- Skip the WSL ROCm bootstrap (root privilege + large downloads, probes
  /dev/dxg) when UNSLOTH_TORCH_INDEX_URL / _FAMILY is set; it previously ran
  before the override was consulted.
- Skip the Radeon/Strix rerouting (which re-probes the GPU and overwrites the
  resolved URL with repo.radeon.com / repo.amd.com) when the index is pinned, so
  an explicit ROCm override (e.g. UNSLOTH_TORCH_INDEX_FAMILY=rocm6.4) is kept.
- install_python_stack.py: derive _TORCH_BACKEND from the override when
  UNSLOTH_TORCH_BACKEND is unset (standalone studio update), so _ensure_rocm_torch
  / _ensure_cuda_torch repair to the requested family instead of re-detecting.
- Strip ALL leading/trailing slashes in the shell override to match the Python
  side (avoids 404s on strict pip proxies).

Adds test cases for double-slash and leading/trailing-slash overrides.

install.sh

@@ -1994,11 +1994,18 @@ get_torch_index_url() {
     # is the convenience form (cpu, cu124, cu126, cu128, cu130, rocm6.4, ...)
     # appended to the mirror base so UNSLOTH_PYTORCH_MIRROR is still honoured.
     if [ -n "${UNSLOTH_TORCH_INDEX_URL:-}" ]; then
-        echo "${UNSLOTH_TORCH_INDEX_URL%/}"; return
+        # Strip ALL trailing slashes (match the Python side's .rstrip("/") and the
+        # Strix mirror handling below) -- a double/triple-slash URL 404s on strict
+        # pip proxies (artifactory, sonatype).
+        _url="${UNSLOTH_TORCH_INDEX_URL}"
+        while [ "${_url%/}" != "$_url" ]; do _url="${_url%/}"; done
+        echo "$_url"; return
     fi
     if [ -n "${UNSLOTH_TORCH_INDEX_FAMILY:-}" ]; then
-        _family="${UNSLOTH_TORCH_INDEX_FAMILY#/}"
-        echo "$_base/${_family%/}"; return
+        _family="${UNSLOTH_TORCH_INDEX_FAMILY}"
+        while [ "${_family#/}" != "$_family" ]; do _family="${_family#/}"; done
+        while [ "${_family%/}" != "$_family" ]; do _family="${_family%/}"; done
+        echo "$_base/$_family"; return
     fi
     # macOS: always CPU (no CUDA support)
     case "$(uname -s)" in Darwin) echo "$_base/cpu"; return ;; esac
@@ -2396,7 +2403,16 @@ _maybe_bootstrap_rocm_wsl() {
     [ -n "$_rw_tmp" ] && rm -f "$_rw_tmp"
     return 0
 }
-_maybe_bootstrap_rocm_wsl || true
+# When the caller pins the wheel index (UNSLOTH_TORCH_INDEX_URL / _FAMILY),
+# honour it everywhere downstream: skip the WSL ROCm bootstrap (which can run
+# sudo + large downloads after probing /dev/dxg) and the Radeon/Strix rerouting
+# below (which would re-probe the GPU and overwrite the pinned URL). A headless /
+# container / CI build must get exactly the index it asked for.
+_torch_index_pinned=false
+if [ -n "${UNSLOTH_TORCH_INDEX_URL:-}" ] || [ -n "${UNSLOTH_TORCH_INDEX_FAMILY:-}" ]; then
+    _torch_index_pinned=true
+fi
+[ "$_torch_index_pinned" = true ] || _maybe_bootstrap_rocm_wsl || true
 
 TORCH_INDEX_URL=$(get_torch_index_url)
 
@@ -2424,7 +2440,11 @@ esac
 # Auto-detect GPU for AMD ROCm based
 # get_torch_index_url must have chosen */rocm*
 # (gfx in rocminfo or amd-smi list). Then require rocminfo "Marketing Name:.*Radeon".
+# Skipped entirely when the index is pinned: an explicit override (even a ROCm
+# one like UNSLOTH_TORCH_INDEX_FAMILY=rocm6.4) must not be rerouted to the
+# Radeon/Strix repos by GPU probing.
 _amd_gpu_radeon=false
+if [ "$_torch_index_pinned" = false ]; then
 case "$TORCH_INDEX_URL" in
     */rocm*)
         if _has_amd_rocm_gpu && command -v rocminfo >/dev/null 2>&1 && \
@@ -2505,6 +2525,7 @@ case "$TORCH_INDEX_URL" in
         fi
         ;;
 esac
+fi  # _torch_index_pinned guard (Radeon + Strix reroute)
 _TAURI_TORCH_INDEX_FAMILY=$(_tauri_torch_index_family "$TORCH_INDEX_URL")
 if [ "$_amd_gpu_radeon" = true ] && [ "$SKIP_TORCH" = false ]; then
     _TAURI_TORCH_INDEX_FAMILY="radeon"

studio/install_python_stack.py

@@ -1429,6 +1429,23 @@ NO_TORCH = _infer_no_torch()
 # GPU detection. Values: "cuda", "rocm", or "cpu". Empty means unknown
 # (standalone `unsloth studio update` runs, where we re-detect normally).
 _TORCH_BACKEND: str = os.environ.get("UNSLOTH_TORCH_BACKEND", "").lower()
+# When install.sh did not run (standalone `unsloth studio update`) but the caller
+# pinned the wheel index explicitly, derive the backend from that override so the
+# CUDA/ROCm repair helpers honour it instead of re-probing the GPU and possibly
+# reinstalling a different family. Classify on the final URL/family segment,
+# mirroring install.sh's UNSLOTH_TORCH_BACKEND case.
+if not _TORCH_BACKEND:
+    _idx_override = (
+        os.environ.get("UNSLOTH_TORCH_INDEX_URL", "").strip()
+        or os.environ.get("UNSLOTH_TORCH_INDEX_FAMILY", "").strip()
+    )
+    _idx_leaf = _idx_override.rstrip("/").rsplit("/", 1)[-1].lower()
+    if _idx_leaf.startswith(("rocm", "gfx")):
+        _TORCH_BACKEND = "rocm"
+    elif _idx_leaf == "cpu":
+        _TORCH_BACKEND = "cpu"
+    elif _idx_leaf.startswith("cu"):
+        _TORCH_BACKEND = "cuda"
 
 
 def _torch_step_label(suffix: str) -> str:

tests/sh/test_get_torch_index_url.sh

@@ -415,6 +415,14 @@ assert_eq "url override beats family override -> url" "https://mirror.example.co
 _result=$(UNSLOTH_TORCH_INDEX_FAMILY="" UNSLOTH_TORCH_INDEX_URL="" run_func "none")
 assert_eq "empty overrides ignored -> detected cpu" "https://download.pytorch.org/whl/cpu" "$_result"
 
+# 46) ALL trailing slashes are stripped from a URL override (not just one).
+_result=$(UNSLOTH_TORCH_INDEX_URL="https://mirror.example.com/whl/cu128///" run_func "none")
+assert_eq "url override double slash stripped" "https://mirror.example.com/whl/cu128" "$_result"
+
+# 47) Leading and trailing slashes stripped from a family override.
+_result=$(UNSLOTH_TORCH_INDEX_FAMILY="//cu128//" run_func "none")
+assert_eq "family override slashes stripped" "https://download.pytorch.org/whl/cu128" "$_result"
+
 rm -f "$_FUNC_FILE"
 rm -rf "$_FAKE_SMI_DIR"
 rm -rf "$_TOOLS_DIR"