test(cli): trim npm mount-path coverage to two invariants

Fold the four salvaged cases into one predicate truth table (WSL drive
mounts and .cmd shims refused, /mnt/data and /usr/bin accepted) and one
resolver test that walks the real re-scan: PATH interop hands back a
Windows npm first, the scan skips the /mnt/c entry and accepts the native
npm under /mnt/data. Drops the dead `hermes_cli.main._is_windows` patch —
the resolver calls main_install_repair's own `_is_windows`, which is
already False on the POSIX hosts these tests run on.

tests/hermes_cli/test_node_runtime_npm_resolution.py

@@ -1,50 +1,34 @@
-"""Regression coverage for POSIX npm path classification."""
+"""POSIX npm path classification: only Windows shims are refused (#112041, #30271)."""
 
 from __future__ import annotations
 
+import os
 from unittest.mock import patch
 
-from hermes_cli.main_install_repair import (
-    _is_windows_npm_path,
-    _resolve_node_runtime_npm,
-)
+from hermes_cli.main_install_repair import _is_windows_npm_path, _resolve_node_runtime_npm
 
 
-def test_windows_npm_path_classifies_only_windows_drive_mounts():
-    assert _is_windows_npm_path("/mnt/c/nodejs/npm")
-    assert not _is_windows_npm_path("/mnt/data/node/bin/npm")
+def test_windows_npm_path_refuses_windows_shims_but_not_native_data_mounts():
+    """A ``/mnt/<drive>`` WSL interop path or a ``.cmd`` shim is Windows npm; a native Linux
+    data mount such as ``/mnt/data`` is not — a folder prefix alone is not a Windows tell."""
+    assert _is_windows_npm_path("/mnt/c/Program Files/nodejs/npm")
+    assert _is_windows_npm_path("/mnt/d/nodejs/npm")
+    assert _is_windows_npm_path("C:\\nodejs\\npm.cmd")
+    assert not _is_windows_npm_path("/mnt/data/hermes/home/.local/bin/npm")
+    assert not _is_windows_npm_path("/usr/bin/npm")
 
 
-def test_resolve_node_runtime_npm_accepts_native_mnt_data_path():
+def test_resolve_node_runtime_npm_rescans_past_windows_drive_to_native_mount(monkeypatch):
+    """When PATH interop hands back a Windows npm first, the re-scan skips the Windows drive
+    mount but still accepts a native npm living under ``/mnt/data``."""
     native_npm = "/mnt/data/node/bin/npm"
+    monkeypatch.setenv("PATH", os.pathsep.join(["/mnt/c/Program Files/nodejs", "/mnt/data/node/bin"]))
+
+    def fake_which(cmd, path=None):
+        return native_npm if path == "/mnt/data/node/bin" else None
+
     with (
-        patch("hermes_cli.main._is_windows", return_value=False),
-        patch("hermes_constants.find_node_executable", return_value=native_npm),
-    ):
-        assert _resolve_node_runtime_npm() == native_npm
-
-
-def test_resolve_node_runtime_npm_rejects_windows_drive_mount(monkeypatch):
-    monkeypatch.setenv("PATH", "/mnt/c/Program Files/nodejs")
-    with (
-        patch("hermes_cli.main._is_windows", return_value=False),
-        patch(
-            "hermes_constants.find_node_executable",
-            return_value="/mnt/c/nodejs/npm",
-        ),
-    ):
-        assert _resolve_node_runtime_npm() is None
-
-
-def test_resolve_node_runtime_npm_rescans_native_mnt_data_path(monkeypatch):
-    native_npm = "/mnt/data/node/bin/npm"
-    monkeypatch.setenv("PATH", "/mnt/data/node/bin")
-    with (
-        patch("hermes_cli.main._is_windows", return_value=False),
-        patch(
-            "hermes_constants.find_node_executable",
-            return_value="/mnt/c/nodejs/npm",
-        ),
-        patch("hermes_cli.main_install_repair.shutil.which", return_value=native_npm),
+        patch("hermes_constants.find_node_executable", return_value="/mnt/c/Program Files/nodejs/npm"),
+        patch("hermes_cli.main_install_repair.shutil.which", side_effect=fake_which),
     ):
         assert _resolve_node_runtime_npm() == native_npm