diff --git a/backend/tests/test_test_config_version_script.py b/backend/tests/test_test_config_version_script.py
new file mode 100644
index 0000000000..213d42d1ba
--- /dev/null
+++ b/backend/tests/test_test_config_version_script.py
@@ -0,0 +1,101 @@
+"""The opt-in config-upgrade wrapper must isolate the suite from the host's uv indexes.
+
+`scripts/test-config-version.sh` exists so a host whose `uv` points at a mirror
+that blocks dependencies can still run `tests/test_config_version.py`. Nothing
+pins that contract today: dropping one of the three `unset` names, or dropping or
+changing the `UV_DEFAULT_INDEX` export, silently restores the failure it was
+added for. These tests run the real script with a stand-in `uv` and assert what
+that child actually received.
+"""
+
+from __future__ import annotations
+
+import os
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+REPO_ROOT = Path(__file__).resolve().parents[2]
+SCRIPT = REPO_ROOT / "scripts" / "test-config-version.sh"
+
+BASH = shutil.which("bash")
+pytestmark = pytest.mark.skipif(BASH is None, reason="requires bash")
+
+STUB = """#!/usr/bin/env bash
+{
+  printf 'UV_INDEX=%s\\n' "${UV_INDEX-<unset>}"
+  printf 'UV_EXTRA_INDEX_URL=%s\\n' "${UV_EXTRA_INDEX_URL-<unset>}"
+  printf 'UV_INDEX_URL=%s\\n' "${UV_INDEX_URL-<unset>}"
+  printf 'UV_DEFAULT_INDEX=%s\\n' "${UV_DEFAULT_INDEX-<unset>}"
+  printf 'ARGS=%s\\n' "$*"
+} > "$STUB_OUT"
+exit 0
+"""
+
+
+def _posix(path: Path) -> str:
+    """Return the path spelling bash needs for PATH on this host."""
+    if os.name != "nt":
+        return str(path)
+    converted = subprocess.run(
+        [BASH or "bash", "-c", 'cygpath -u "$1"', "cygpath", str(path)],
+        capture_output=True,
+        text=True,
+        check=True,
+    )
+    return converted.stdout.strip()
+
+
+def _run_wrapper(tmp_path: Path, extra_env: dict[str, str]) -> dict[str, str]:
+    assert SCRIPT.is_file(), f"{SCRIPT} must exist"
+
+    bin_dir = tmp_path / "bin"
+    bin_dir.mkdir()
+    stub = bin_dir / "uv"
+    stub.write_text(STUB, encoding="utf-8", newline="")
+    stub.chmod(0o755)
+
+    captured = tmp_path / "captured.env"
+    env = {key: value for key, value in os.environ.items() if not key.startswith("UV_")}
+    env.update(extra_env)
+    env["STUB_OUT"] = _posix(captured)
+    env["PATH"] = f"{_posix(bin_dir)}{os.pathsep}{env.get('PATH', '')}"
+
+    result = subprocess.run(
+        [BASH or "bash", str(SCRIPT), "--deselect", "sentinel"],
+        cwd=REPO_ROOT,
+        env=env,
+        capture_output=True,
+        text=True,
+        encoding="utf-8",
+        errors="replace",
+    )
+    assert result.returncode == 0, f"wrapper failed: {result.stdout}\n{result.stderr}"
+    assert captured.is_file(), f"the stand-in uv never ran: {result.stdout}\n{result.stderr}"
+
+    return dict(line.split("=", 1) for line in captured.read_text(encoding="utf-8").splitlines() if "=" in line)
+
+
+def test_wrapper_clears_host_indexes_and_selects_public_pypi(tmp_path):
+    captured = _run_wrapper(
+        tmp_path,
+        {
+            "UV_INDEX": "https://mirror.invalid/simple",
+            "UV_EXTRA_INDEX_URL": "https://extra.invalid/simple",
+            "UV_INDEX_URL": "https://legacy.invalid/simple",
+        },
+    )
+
+    assert captured["UV_INDEX"] == "<unset>"
+    assert captured["UV_EXTRA_INDEX_URL"] == "<unset>"
+    assert captured["UV_INDEX_URL"] == "<unset>"
+    assert captured["UV_DEFAULT_INDEX"] == "https://pypi.org/simple"
+
+
+def test_wrapper_runs_the_config_version_suite_and_forwards_arguments(tmp_path):
+    captured = _run_wrapper(tmp_path, {})
+
+    assert captured["ARGS"].startswith("run --locked pytest -q tests/test_config_version.py")
+    assert "--deselect sentinel" in captured["ARGS"]