Add tests and docs for '--' argument separator requirement

- Add TestArgumentSeparator class with 8 tests verifying that script
  arguments must come after '--' separator
- Update create and edit command docstrings with examples showing
  correct usage of '--' separator
- Update argument help text to indicate "(must come after '--')"
- Add "Passing Arguments to Your Script" section to README

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

test_mcquack.py

@@ -214,6 +214,99 @@ class TestDelete:
         assert "does not exist" in result.output
 
 
+class TestArgumentSeparator:
+    """Tests verifying that '--' separator is required for passing arguments to scripts.
+
+    This ensures that:
+    - 'mcquack create script.sh --help' shows help for the create command
+    - 'mcquack create script.sh -- --help' creates a plist with --help as a script arg
+    """
+
+    def test_create_help_without_separator(self, mock_dirs, mock_script, mock_launchctl):
+        """Verify that --help without -- shows create command help, not passed to script."""
+        result = runner.invoke(app, ["create", str(mock_script), "--help"])
+        assert result.exit_code == 0
+        # Should show help text for create command
+        assert "Create and load a LaunchAgent" in result.stdout or "Usage:" in result.stdout
+        # Should NOT have created a plist
+        plist_path = get_plist_path(mock_dirs)
+        assert not plist_path.exists()
+
+    def test_create_help_with_separator(self, mock_dirs, mock_script, mock_launchctl):
+        """Verify that -- --help passes --help as an argument to the script."""
+        result = runner.invoke(app, ["create", str(mock_script), "--", "--help"])
+        assert result.exit_code == 0
+        assert "Created:" in result.stdout
+
+        # Verify --help is in the plist as a script argument
+        plist_path = get_plist_path(mock_dirs)
+        assert plist_path.exists()
+        program_args = read_plist_args(plist_path)
+        assert "--help" in program_args
+        assert program_args[1] == "--help"
+
+    def test_create_verbose_without_separator(self, mock_dirs, mock_script, mock_launchctl):
+        """Verify that --verbose without -- is treated as unknown option, not script arg."""
+        result = runner.invoke(app, ["create", str(mock_script), "--verbose"])
+        # Typer should reject unknown options
+        assert result.exit_code != 0
+        assert "No such option" in result.output or "no such option" in result.output.lower()
+        # Should NOT have created a plist
+        plist_path = get_plist_path(mock_dirs)
+        assert not plist_path.exists()
+
+    def test_create_verbose_with_separator(self, mock_dirs, mock_script, mock_launchctl):
+        """Verify that -- --verbose passes --verbose as an argument to the script."""
+        result = runner.invoke(app, ["create", str(mock_script), "--", "--verbose"])
+        assert result.exit_code == 0
+
+        plist_path = get_plist_path(mock_dirs)
+        program_args = read_plist_args(plist_path)
+        assert "--verbose" in program_args
+
+    def test_edit_help_without_separator(self, mock_dirs, mock_script, mock_launchctl):
+        """Verify that edit --help shows edit command help."""
+        # First create an agent
+        runner.invoke(app, ["create", str(mock_script)])
+
+        result = runner.invoke(app, ["edit", str(mock_script), "--help"])
+        assert result.exit_code == 0
+        assert "Edit the arguments" in result.stdout or "Usage:" in result.stdout
+
+    def test_edit_help_with_separator(self, mock_dirs, mock_script, mock_launchctl):
+        """Verify that edit -- --help passes --help as a new argument."""
+        # First create an agent
+        runner.invoke(app, ["create", str(mock_script)])
+
+        result = runner.invoke(app, ["edit", str(mock_script), "--", "--help"])
+        assert result.exit_code == 0
+
+        plist_path = get_plist_path(mock_dirs)
+        program_args = read_plist_args(plist_path)
+        assert "--help" in program_args
+
+    def test_create_mixed_args_with_separator(self, mock_dirs, mock_script, mock_launchctl):
+        """Verify multiple dash-prefixed args after -- are all passed to script."""
+        result = runner.invoke(app, ["create", str(mock_script), "--", "--config", "/path", "--debug", "-v"])
+        assert result.exit_code == 0
+
+        plist_path = get_plist_path(mock_dirs)
+        program_args = read_plist_args(plist_path)
+        # All args after -- should be in the plist
+        assert program_args[1:] == ["--config", "/path", "--debug", "-v"]
+
+    def test_create_double_dash_as_argument(self, mock_dirs, mock_script, mock_launchctl):
+        """Verify that -- can be passed as a script argument using -- --."""
+        result = runner.invoke(app, ["create", str(mock_script), "--", "--", "arg_after_double_dash"])
+        assert result.exit_code == 0
+
+        plist_path = get_plist_path(mock_dirs)
+        program_args = read_plist_args(plist_path)
+        # The first -- is consumed by typer, the second becomes an argument
+        assert "--" in program_args
+        assert "arg_after_double_dash" in program_args
+
+
 class TestPlistFormat:
     """Tests verifying plist file format independently of plistlib."""