diff --git a/scripts/run_tests.sh b/scripts/run_tests.sh
index 24ad3e8409ec7..f3395734845d1 100755
--- a/scripts/run_tests.sh
+++ b/scripts/run_tests.sh
@@ -77,6 +77,20 @@ fi
 # ── Run in hermetic env ──────────────────────────────────────────────────────
 # env -i: start with empty environment, opt-in only what we need.
 # No credential var can leak — you'd have to explicitly add it here.
+#
+# On Windows, Python's pathlib.Path.home() does not use the POSIX HOME alias;
+# it resolves USERPROFILE or HOMEDRIVE+HOMEPATH. Preserve only those non-secret
+# home-resolution variables so env -i remains hermetic without creating a
+# literal '~' path or breaking Windows tests.
+WINDOWS_HOME_ENV=()
+if [[ -n "${USERPROFILE:-}" || -n "${HOMEDRIVE:-}${HOMEPATH:-}" ]]; then
+  for name in USERPROFILE HOMEDRIVE HOMEPATH; do
+    if [[ -n "${!name:-}" ]]; then
+      WINDOWS_HOME_ENV+=("$name=${!name}")
+    fi
+  done
+fi
+
 echo "▶ running per-file parallel test suite via run_tests_parallel.py"
 echo "  (TZ=UTC LANG=C.UTF-8 PYTHONHASHSEED=0; clean env)"
 
@@ -94,6 +108,7 @@ echo "▶ launching test runner"
 exec env -i \
   PATH="$PATH" \
   HOME="$HOME" \
+  "${WINDOWS_HOME_ENV[@]}" \
   TZ=UTC \
   LANG=C.UTF-8 \
   LC_ALL=C.UTF-8 \
diff --git a/tests/plugins/memory/test_hindsight_provider.py b/tests/plugins/memory/test_hindsight_provider.py
index 5cd485d4c1ad7..1083d8df9eeb3 100644
--- a/tests/plugins/memory/test_hindsight_provider.py
+++ b/tests/plugins/memory/test_hindsight_provider.py
@@ -10,6 +10,7 @@
 import re
 import stat
 import sys
+from pathlib import Path
 from types import SimpleNamespace
 from unittest.mock import AsyncMock, MagicMock
 
@@ -36,8 +37,8 @@
 
 
 @pytest.fixture(autouse=True)
-def _clean_env(monkeypatch):
-    """Ensure no stale env vars leak between tests."""
+def _clean_env(tmp_path, monkeypatch):
+    """Ensure no stale env vars or Windows home state leak between tests."""
     for key in (
         "HINDSIGHT_API_KEY", "HINDSIGHT_API_URL", "HINDSIGHT_BANK_ID",
         "HINDSIGHT_BUDGET", "HINDSIGHT_MODE", "HINDSIGHT_TIMEOUT",
@@ -48,6 +49,12 @@ def _clean_env(monkeypatch):
     ):
         monkeypatch.delenv(key, raising=False)
 
+    # On Windows pathlib.Path.home() resolves USERPROFILE/HOMEDRIVE+HOMEPATH,
+    # not the POSIX HOME alias that these tests historically monkeypatched.
+    # Patch the actual API and keep all legacy profile writes in tmp_path.
+    isolated_home = tmp_path / "user-home"
+    monkeypatch.setattr(Path, "home", classmethod(lambda cls: isolated_home))
+
 
 def _make_mock_client():
     """Create a mock Hindsight client with async methods."""
diff --git a/tests/test_run_tests_shell_env.py b/tests/test_run_tests_shell_env.py
new file mode 100644
index 0000000000000..459b2b621b7e0
--- /dev/null
+++ b/tests/test_run_tests_shell_env.py
@@ -0,0 +1,15 @@
+"""Windows regression tests for the canonical hermetic runner."""
+
+import os
+from pathlib import Path
+
+import pytest
+
+
+@pytest.mark.skipif(os.name != "nt", reason="Windows home resolution is the behavior under test")
+def test_runner_preserves_windows_home_resolution():
+    """Path.home() must resolve when run under scripts/run_tests.sh."""
+    actual = Path.home()
+    expected = os.environ.get("USERPROFILE")
+    assert expected, "canonical runner dropped USERPROFILE"
+    assert actual == Path(expected)