fix(skills): preserve escapes in Python workspace shell wrapper (#2666)

* fix(skills): preserve escapes in Python workspace shell wrapper

* style(skills): retain original end-of-file formatting

src/langbot/pkg/utils/python_workspace.py

@@ -49,7 +49,7 @@ def wrap_python_command_with_env(
 
     writable_state_path = state_path or mount_path
     bootstrap = textwrap.dedent(
-        f"""
+        rf"""
         set -e
 
         _LB_VENV_DIR="{writable_state_path}/.venv"

tests/unit_tests/utils/test_python_workspace.py

@@ -0,0 +1,78 @@
+"""Exercise generated shell/Python syntax without installing dependencies."""
+
+import hashlib
+import json
+import os
+from pathlib import Path
+import shlex
+import shutil
+import subprocess
+import sys
+import tempfile
+import unittest
+
+from langbot.pkg.utils.python_workspace import wrap_python_command_with_env
+
+
+class TestPythonWorkspaceCommand(unittest.TestCase):
+    def test_generated_command_contains_no_null_bytes(self):
+        command = wrap_python_command_with_env('python main.py')
+        self.assertNotIn('\0', command)
+
+    @unittest.skipUnless(shutil.which('sh'), 'POSIX shell required')
+    def test_generated_command_has_valid_shell_syntax(self):
+        command = wrap_python_command_with_env('python main.py')
+        result = subprocess.run(['sh', '-n', '-c', command], capture_output=True, text=True, timeout=10)
+        self.assertEqual(result.returncode, 0, result.stderr)
+
+    @unittest.skipUnless(shutil.which('sh'), 'POSIX shell required')
+    def test_cached_environment_executes_command_and_hashes_manifest(self):
+        with tempfile.TemporaryDirectory() as directory:
+            root = Path(directory)
+            mount = root / 'project'
+            state = root / 'state'
+            bin_dir = root / 'bin'
+            venv_bin = state / '.venv' / 'bin'
+            meta_dir = state / '.langbot'
+            for path in (mount, bin_dir, venv_bin, meta_dir):
+                path.mkdir(parents=True)
+
+            manifest = b'# local fixture\nexample==1.0\n'
+            (mount / 'requirements.txt').write_bytes(manifest)
+            # Run the real metadata interpreter, but fail closed if bootstrap is attempted.
+            system_python = bin_dir / 'python3'
+            system_python.write_text(
+                '#!/bin/sh\n'
+                '[ "$#" -eq 1 ] && [ "$1" = "-" ] || exit 99\n'
+                f'exec {shlex.quote(sys.executable)} "$@"\n',
+                encoding='utf-8',
+            )
+            system_python.chmod(0o755)
+            venv_python = venv_bin / 'python'
+            venv_python.write_text('#!/bin/sh\nprintf "%s\\n" "$VIRTUAL_ENV"\n', encoding='utf-8')
+            venv_python.chmod(0o755)
+            metadata = json.dumps(
+                {
+                    'python_executable': sys.executable,
+                    'python_version': list(sys.version_info[:3]),
+                    'manifest_files': ['requirements.txt'],
+                    'manifest_sha256': hashlib.sha256(b'requirements.txt\0' + manifest + b'\0').hexdigest(),
+                },
+                sort_keys=True,
+            )
+            meta_file = meta_dir / 'python-env.json'
+            meta_file.write_text(metadata, encoding='utf-8')
+
+            command = wrap_python_command_with_env('python', mount_path=str(mount), state_path=str(state))
+            result = subprocess.run(
+                ['sh', '-c', command],
+                env={**os.environ, 'PATH': f'{bin_dir}{os.pathsep}{os.environ.get("PATH", "")}'},
+                capture_output=True,
+                text=True,
+                timeout=10,
+            )
+
+            self.assertEqual(result.returncode, 0, result.stderr)
+            self.assertEqual(result.stdout, f'{state / ".venv"}\n')
+            self.assertEqual(meta_file.read_text(encoding='utf-8'), metadata)
+            self.assertFalse((meta_dir / 'python-env.lock').exists())