diff --git a/hermes_cli/bang_shell.py b/hermes_cli/bang_shell.py
index 706f1e149e..6753d43283 100644
--- a/hermes_cli/bang_shell.py
+++ b/hermes_cli/bang_shell.py
@@ -90,13 +90,11 @@ def _bang_env() -> dict:
     """Environment for a bang command with Hermes-managed secrets filtered.
 
     The CLI process holds every provider API key; a user-typed command may still run a third-party
-    script, so reuse the sanitizer ``quick_commands`` and the local terminal backend use.
+    script, so reuse the sanitizer ``quick_commands`` and the local terminal backend use. If that
+    boundary is unavailable, let the launch fail rather than passing the CLI's full environment.
     """
-    try:
-        from tools.environments.local import build_subprocess_env
-        return build_subprocess_env()  # == _sanitize_subprocess_env(os.environ.copy())
-    except Exception:
-        return os.environ.copy()  # tools package unimportable: run the user's command anyway
+    from tools.environments.local import build_subprocess_env
+    return build_subprocess_env()
 
 
 def run_bang_command(command: str, *, cwd: Optional[str] = None, timeout: int = DEFAULT_TIMEOUT, writer=None) -> int:
diff --git a/tests/hermes_cli/test_bang_shell_mode.py b/tests/hermes_cli/test_bang_shell_mode.py
index 63fedde30d..ae74a1a0ed 100644
--- a/tests/hermes_cli/test_bang_shell_mode.py
+++ b/tests/hermes_cli/test_bang_shell_mode.py
@@ -5,6 +5,7 @@ invoked for a dangerous command, that non-zero exit codes surface, and the
 load-bearing invariant: a bang command leaves conversation_history
 byte-identical because it never becomes a turn.
 """
+import builtins
 import copy
 import json
 import os
@@ -121,6 +122,23 @@ class TestBangExecution:
         assert code == 0
         assert "ok" in lines
 
+    def test_unavailable_environment_sanitizer_prevents_launch(self):
+        lines = []
+        real_import = builtins.__import__
+
+        def block_sanitizer(name, *args, **kwargs):
+            if name == "tools.environments.local":
+                raise ImportError("environment sanitizer unavailable")
+            return real_import(name, *args, **kwargs)
+
+        with patch("builtins.__import__", block_sanitizer), \
+             patch("hermes_cli.bang_shell.subprocess.Popen") as popen:
+            code = run_bang_command("echo must-not-run", writer=lines.append)
+
+        assert code == 127
+        popen.assert_not_called()
+        assert any("failed to run command" in line for line in lines)
+
 
 # ── CLI handler: approval gate, usage hint, exit codes ─────────────────────