diff --git a/hermes_cli/relaunch.py b/hermes_cli/relaunch.py
index c254184fe9..a5a8431fbe 100644
--- a/hermes_cli/relaunch.py
+++ b/hermes_cli/relaunch.py
@@ -84,18 +84,34 @@ def resolve_hermes_bin() -> Optional[str]:
       1. ``sys.argv[0]`` if it resolves to a real executable.
       2. ``shutil.which("hermes")`` on PATH.
       3. ``None`` → caller should fall back to ``python -m hermes_cli.main``.
+
+    Windows note: ``os.access(path, os.X_OK)`` returns True for ``.py`` and
+    ``.pyc`` files on Windows (the OS treats anything listed in PATHEXT as
+    executable, and Python files are often registered there).  But
+    ``subprocess.run([script.py, ...])`` can't actually execute a .py
+    directly — CreateProcessW needs a real .exe, not a script associated
+    with the Python launcher.  On Windows we therefore skip the argv[0]
+    fast-path when it points at a .py file and fall through to either
+    ``hermes.exe`` on PATH or the ``sys.executable -m hermes_cli.main``
+    fallback.
     """
     argv0 = sys.argv[0]
+    _is_windows = sys.platform == "win32"
+
+    def _is_python_script(p: str) -> bool:
+        return p.lower().endswith((".py", ".pyc"))
 
     # Absolute path to an executable (covers nix store, venv wrappers, etc.)
     if os.path.isabs(argv0) and os.path.isfile(argv0) and os.access(argv0, os.X_OK):
-        return argv0
+        if not (_is_windows and _is_python_script(argv0)):
+            return argv0
 
     # Relative path — resolve against CWD
     if not argv0.startswith("-") and os.path.isfile(argv0):
         abs_path = os.path.abspath(argv0)
         if os.access(abs_path, os.X_OK):
-            return abs_path
+            if not (_is_windows and _is_python_script(abs_path)):
+                return abs_path
 
     # PATH lookup
     path_bin = shutil.which("hermes")
diff --git a/scripts/install.ps1 b/scripts/install.ps1
index 13af38953b..2ffca87adb 100644
--- a/scripts/install.ps1
+++ b/scripts/install.ps1
@@ -963,9 +963,17 @@ function Install-NodeDeps {
         return
     }
 
-    # Resolve npm.cmd to an absolute path so PATHEXT doesn't bite us when
-    # the installer runs in a session that hasn't refreshed PATH since the
-    # Node.js install.  Get-Command respects PATHEXT.
+    # Resolve npm explicitly to npm.cmd, NOT npm.ps1.  Node.js on Windows
+    # ships BOTH npm.cmd (a batch shim) and npm.ps1 (a PowerShell shim).
+    # Get-Command's default ordering picks whichever comes first in PATHEXT,
+    # and on many systems that's .ps1 — but .ps1 requires scripts to be
+    # enabled in PowerShell's execution policy, which most Windows users
+    # don't have (the Restricted / RemoteSigned default blocks unsigned
+    # .ps1 files).  .cmd has no such restriction and works on every box.
+    #
+    # Strategy: look next to the npm shim we found and prefer npm.cmd if
+    # it exists in the same directory.  Fall back to whatever Get-Command
+    # returned if we can't find a .cmd sibling.
     $npmCmd = Get-Command npm -ErrorAction SilentlyContinue
     if (-not $npmCmd) {
         Write-Warn "npm not found on PATH — skipping Node.js dependencies."
@@ -973,6 +981,16 @@ function Install-NodeDeps {
         return
     }
     $npmExe = $npmCmd.Source
+    if ($npmExe -like "*.ps1") {
+        $npmCmdSibling = Join-Path (Split-Path $npmExe -Parent) "npm.cmd"
+        if (Test-Path $npmCmdSibling) {
+            Write-Info "Using npm.cmd (PowerShell execution policy blocks npm.ps1)"
+            $npmExe = $npmCmdSibling
+        } else {
+            Write-Warn "Only npm.ps1 available — install may fail if script execution is disabled."
+            Write-Info "  If it fails, either enable PS script execution or install Node via winget."
+        }
+    }
 
     # Helper: run "npm install" in a given directory and surface the real
     # error when it fails.  Returns $true on success.
diff --git a/tests/hermes_cli/test_relaunch.py b/tests/hermes_cli/test_relaunch.py
index 4658c678fd..1b4f4ff154 100644
--- a/tests/hermes_cli/test_relaunch.py
+++ b/tests/hermes_cli/test_relaunch.py
@@ -229,4 +229,58 @@ class TestRelaunch:
         assert exc_info.value.code == 1
         err = capsys.readouterr().err
         assert "relaunch failed" in err
-        assert "open a new terminal" in err.lower() or "path" in err.lower()
\ No newline at end of file
+        assert "open a new terminal" in err.lower() or "path" in err.lower()
+
+
+class TestResolveHermesBinWindowsPyGuard:
+    """On Windows, resolve_hermes_bin MUST NOT return a .py path.
+    os.access(x, os.X_OK) returns True for .py files on Windows because
+    PATHEXT includes .py when the Python launcher is installed — but
+    subprocess.run can't actually exec a .py directly, so the relaunch
+    would fail with the cryptic "%1 is not a valid Win32 application" error.
+    """
+
+    def test_windows_rejects_py_argv0_falls_through_to_path(self, monkeypatch, tmp_path):
+        """On Windows, if sys.argv[0] is a .py file, we must skip the
+        argv[0] fast-path and fall through to PATH / python -m."""
+        # Build a fake .py script that "passes" the isfile + X_OK checks.
+        script = tmp_path / "main.py"
+        script.write_text("# stub")
+
+        monkeypatch.setattr(relaunch_mod.sys, "platform", "win32")
+        monkeypatch.setattr(relaunch_mod.sys, "argv", [str(script), "chat"])
+        # Force PATH lookup to return a hermes.exe so the test doesn't
+        # exercise the None-fallback path (that's a separate test).
+        monkeypatch.setattr(
+            relaunch_mod.shutil, "which",
+            lambda name: r"C:\venv\Scripts\hermes.exe" if name == "hermes" else None,
+        )
+
+        bin_path = relaunch_mod.resolve_hermes_bin()
+        # Must NOT be the .py — must be the hermes.exe PATH entry.
+        assert bin_path == r"C:\venv\Scripts\hermes.exe"
+
+    def test_posix_still_accepts_py_argv0(self, monkeypatch, tmp_path):
+        """POSIX behaviour unchanged: argv[0] pointing at an executable
+        script (including .py with a shebang + chmod +x) is fine to return
+        because POSIX exec can route through the shebang line."""
+        if sys.platform == "win32":
+            pytest.skip("POSIX semantics")
+        script = tmp_path / "hermes"
+        script.write_text("#!/usr/bin/env python3\n")
+        script.chmod(0o755)
+        monkeypatch.setattr(relaunch_mod.sys, "argv", [str(script), "chat"])
+        assert relaunch_mod.resolve_hermes_bin() == str(script)
+
+    def test_windows_py_argv0_with_no_hermes_on_path_returns_none(self, monkeypatch, tmp_path):
+        """Bulletproof fallback: if argv0 is .py on Windows AND hermes.exe
+        isn't on PATH, return None so the caller falls back to
+        python -m hermes_cli.main."""
+        script = tmp_path / "main.py"
+        script.write_text("# stub")
+
+        monkeypatch.setattr(relaunch_mod.sys, "platform", "win32")
+        monkeypatch.setattr(relaunch_mod.sys, "argv", [str(script), "chat"])
+        monkeypatch.setattr(relaunch_mod.shutil, "which", lambda name: None)
+
+        assert relaunch_mod.resolve_hermes_bin() is None