install: keep pinned repairs off UV_TORCH_BACKEND and narrow setup.ps1's rocm pin match

Round 2 of the pinned-index hardening:

1. _build_uv_cmd converted UV_TORCH_BACKEND into --torch-backend before the
   new env isolation could act, and uv's torch backend redirects torch
   resolution to its own per-backend index even when --index-url is given
   (verified: a cu128-pinned dry run with UV_TORCH_BACKEND=cpu resolves
   torch 2.13.0+cpu). Pinned-index commands now never receive the flag and
   UV_TORCH_BACKEND joins the stripped env vars, so uv cannot re-read it.

2. setup.ps1's pinned reroute had the same bare rocm* glob install.ps1 had:
   a custom find-links leaf like rocm-rel-7.2.1 was routed through the ROCm
   --index-url path instead of the verbatim unknown-pin path. Now requires
   a digit after rocm, matching install.ps1, install.sh and
   _is_pip_rocm_family_leaf.

3. The marker test's case-normalization checks used -eq, which is
   case-insensitive in PowerShell, making them vacuous, and the unknown-leaf
   expectation was written lowercased while the implementation deliberately
   preserves custom-leaf case. Tightened to -ceq with the case-preserving
   expected value.

Adds unit + parity tests for 1 and 2 (5 new tests).

studio/install_python_stack.py

@@ -2560,9 +2560,13 @@ def _build_uv_cmd(args: tuple[str, ...]) -> list[str]:
     cmd.extend(_translate_pip_args_for_uv(args))
     # Torch is pre-installed by install.sh/setup.ps1. Do not add
     # --torch-backend by default -- it can cause solver dead-ends on CPU-only
-    # machines. Callers that need it can set UV_TORCH_BACKEND.
+    # machines. Callers that need it can set UV_TORCH_BACKEND. Never add it to a
+    # pinned-index command: uv's torch backend redirects torch resolution to its
+    # own per-backend index (verified: --index-url .../cu128 with UV_TORCH_BACKEND
+    # =cpu resolves torch+cpu), which would defeat the explicit pin exactly like
+    # the index env vars _install_env_for_cmd() strips.
     _tb = os.environ.get("UV_TORCH_BACKEND", "")
-    if _tb:
+    if _tb and not _is_pinned_index_cmd(cmd):
         cmd.append(f"--torch-backend={_tb}")
     return cmd
 
@@ -2576,7 +2580,22 @@ def _build_uv_cmd(args: tuple[str, ...]) -> list[str]:
 # actually used. install.sh (run_install_cmd, #6898), install.ps1 and setup.ps1
 # already neutralise these vars for their pinned installs; do the same here so the
 # pin wins on every platform. Non-pinned installs (no --index-url) keep the mirror.
-_UV_INDEX_ENV_VARS = ("UV_DEFAULT_INDEX", "UV_INDEX_URL", "UV_INDEX", "UV_EXTRA_INDEX_URL")
+# UV_TORCH_BACKEND is stripped too: uv's torch backend redirects torch resolution
+# to its own per-backend index even when a --index-url is given, so it defeats a
+# pin the same way ( _build_uv_cmd also refuses to turn it into a --torch-backend
+# flag for pinned commands; this covers uv reading the env var directly).
+_UV_INDEX_ENV_VARS = (
+    "UV_DEFAULT_INDEX",
+    "UV_INDEX_URL",
+    "UV_INDEX",
+    "UV_EXTRA_INDEX_URL",
+    "UV_TORCH_BACKEND",
+)
+
+
+def _is_pinned_index_cmd(cmd: "list[str] | tuple[str, ...]") -> bool:
+    """True when the command pins an index via --index-url / --default-index."""
+    return any(arg in ("--index-url", "--default-index") for arg in cmd)
 
 
 def _install_env_for_cmd(cmd: "list[str]") -> "dict[str, str] | None":
@@ -2585,11 +2604,12 @@ def _install_env_for_cmd(cmd: "list[str]") -> "dict[str, str] | None":
     Returns None (inherit the caller's environment unchanged) when the command
     does NOT pin an index, so ordinary installs still honour a user's UV_INDEX /
     UV_EXTRA_INDEX_URL mirror. When the command passes --index-url / --default-index
-    (the torch repair paths), the four uv index env vars are removed so the pinned
-    index is not overridden by an inherited mirror (uv treats the default index as
-    lowest priority). Mirrors install.sh's run_install_cmd gate (#6898).
+    (the torch repair paths), the uv index env vars (and UV_TORCH_BACKEND) are
+    removed so the pinned index is not overridden by an inherited mirror or torch
+    backend (uv treats the default index as lowest priority). Mirrors install.sh's
+    run_install_cmd gate (#6898).
     """
-    if not any(arg in ("--index-url", "--default-index") for arg in cmd):
+    if not _is_pinned_index_cmd(cmd):
         return None
     env = os.environ.copy()
     for name in _UV_INDEX_ENV_VARS:

studio/setup.ps1

@@ -3168,10 +3168,15 @@ if ($TorchIndexPinned -and -not $ROCmIndexUrl -and $PinnedTorchIndexUrl) {
         $ROCmVisionSpec = "torchvision>=0.26.0,<0.27.0"
         $ROCmAudioSpec  = "torchaudio>=2.11.0,<2.12.0"
         substep "pinned ROCm index ($_pinLeaf) -- enforcing $ROCmTorchSpec" "Cyan"
-    } elseif ($_pinLeaf -like 'gfx*' -or $_pinLeaf -like 'rocm*') {
+    } elseif ($_pinLeaf -like 'gfx*' -or $_pinLeaf -match '^rocm\d') {
         # Other gfx per-arch indexes and older rocm (<=7.1) ship torch <2.11;
         # route via the ROCm path with bare specs (matches the automatic path's
         # bare floor for these arches).
+        # Require a DIGIT after rocm (rocm7.1, not rocm-rel-7.2.1 / rocm-current):
+        # only rocm<digit> and gfx* are pip --index-url (PEP 503) families; a
+        # rocm-<nondigit> leaf is a custom/find-links URL that must stay on the
+        # verbatim unknown-pin path. Mirrors install.ps1 and
+        # install_python_stack.py's _is_pip_rocm_family_leaf (^rocm\d).
         $ROCmIndexUrl   = $PinnedTorchIndexUrl
         $ROCmTorchSpec  = "torch"
         $ROCmVisionSpec = "torchvision"

tests/python/test_cross_platform_parity.py

@@ -485,6 +485,17 @@ class TestPinnedRocmLeafDigitParity:
             "-like 'rocm*'" not in text
         ), "install.ps1 must not route a pinned index on a bare -like 'rocm*' glob"
 
+    def test_setup_ps1_pinned_reroute_requires_rocm_digit(self):
+        text = SETUP_PS1.read_text(encoding = "utf-8")
+        assert "-match '^rocm\\d'" in text, (
+            "setup.ps1 pinned-index reroute must use -match '^rocm\\d' (not a bare "
+            "-like 'rocm*' glob) so custom find-links leaves stay on the verbatim path"
+        )
+        pinned_block = text[text.find("$_pinGfx211 = Test-RocmGfx211Leaf") :][:2000]
+        assert "-like 'rocm*'" not in pinned_block, (
+            "setup.ps1 pinned reroute must not route on a bare -like 'rocm*' glob"
+        )
+
     def test_install_sh_repairable_requires_rocm_digit(self):
         text = INSTALL_SH.read_text(encoding = "utf-8")
         assert re.search(

tests/python/test_install_python_stack.py

@@ -54,6 +54,24 @@ class TestBuildUvCmdTorchBackend:
             a.startswith("--torch-backend") for a in cmd
         ), f"Empty UV_TORCH_BACKEND should not add flag, got: {cmd}"
 
+    def test_uv_torch_backend_skipped_for_pinned_index(self):
+        """A pinned-index command must NOT get --torch-backend: uv's torch backend
+        redirects torch resolution to its own per-backend index even when
+        --index-url is given (verified: cu128 pin + backend cpu installs
+        torch+cpu), defeating the pin."""
+        for pin_flag in ("--index-url", "--default-index"):
+            with mock.patch.dict(os.environ, {"UV_TORCH_BACKEND": "cpu"}):
+                cmd = self._call(("torch", pin_flag, "https://download.pytorch.org/whl/cu128"))
+            assert not any(
+                a.startswith("--torch-backend") for a in cmd
+            ), f"{pin_flag} command must not carry --torch-backend, got: {cmd}"
+
+    def test_uv_torch_backend_kept_for_unpinned(self):
+        """Non-pinned commands still honour UV_TORCH_BACKEND."""
+        with mock.patch.dict(os.environ, {"UV_TORCH_BACKEND": "cpu"}):
+            cmd = self._call(("somepackage",))
+        assert "--torch-backend=cpu" in cmd
+
 
 class TestUvSafePath:
     """_uv_safe_path hands uv a space-free `-c`/`-r` path (issue #6503)."""
@@ -216,3 +234,10 @@ class TestPinnedIndexClearsUvEnv:
             env = ips._install_env_for_cmd(cmd)
         assert env is not None
         assert env.get("PATH_SENTINEL_XYZ") == "keepme", "only uv index vars are removed"
+
+    def test_pinned_cmd_strips_uv_torch_backend(self):
+        """UV_TORCH_BACKEND is stripped for pinned commands so uv cannot read it
+        from the environment and reroute torch off the pinned index."""
+        with mock.patch.dict(os.environ, {"UV_TORCH_BACKEND": "cpu"}):
+            env = ips._install_env_for_cmd(["uv", "pip", "install", "torch", "--index-url", "https://x/cu128"])
+        assert env is not None and "UV_TORCH_BACKEND" not in env

tests/studio/test_torch_index_marker.ps1

@@ -39,12 +39,14 @@ function Check($name, $cond) {
 }
 
 Write-Host "Get-NormalizedIndexUrl (trim / strip trailing slash / lowercase leaf)"
-Check "trailing slashes + leaf lowered" `
-    ((Get-NormalizedIndexUrl "https://repo.amd.com/rocm/whl/gfx120X-all///") -eq "https://repo.amd.com/rocm/whl/gfx120x-all")
+# -ceq: PowerShell -eq is case-INsensitive for strings, which would make these
+# case-normalization checks vacuous (any casing would pass).
+Check "trailing slashes + known family leaf lowered" `
+    ((Get-NormalizedIndexUrl "https://repo.amd.com/rocm/whl/gfx120X-all///") -ceq "https://repo.amd.com/rocm/whl/gfx120x-all")
 Check "whitespace trimmed" `
-    ((Get-NormalizedIndexUrl "  https://download.pytorch.org/whl/cu128  ") -eq "https://download.pytorch.org/whl/cu128")
-Check "host case preserved, leaf lowered" `
-    ((Get-NormalizedIndexUrl "https://Mirror.Local/Simple/") -eq "https://Mirror.Local/simple")
+    ((Get-NormalizedIndexUrl "  https://download.pytorch.org/whl/cu128  ") -ceq "https://download.pytorch.org/whl/cu128")
+Check "host case preserved, unknown custom leaf keeps case" `
+    ((Get-NormalizedIndexUrl "https://Mirror.Local/Simple/") -ceq "https://Mirror.Local/Simple")
 Check "gfx120X-all == gfx120x-all after normalize" `
     ((Get-NormalizedIndexUrl "https://repo.amd.com/rocm/whl/gfx120X-all") -eq (Get-NormalizedIndexUrl "https://repo.amd.com/rocm/whl/gfx120x-all"))
 Check "empty -> null" ($null -eq (Get-NormalizedIndexUrl "   "))