Function desktop_exec_escape 

fn desktop_exec_escape(exe: &Path) -> String

Escape a path for use inside a quoted argument of a desktop entry’s Exec= value.

Stripping newlines is not enough (ReAgent/Codex P2 on PR #2999). All of these are legal in a Unix path and all of them change how the desktop-entry parser tokenizes the command:

• " terminates the quoted argument — the rest of the path becomes separate argv entries, so the app is launched with the wrong executable.
• \, `, $ are reserved inside quoted arguments per the Desktop Entry Specification and must be backslash-escaped.
• % introduces a field code (%f, %U, …); an unescaped one is substituted by the launcher. The spec’s escape for a literal is %%.
• newline/CR would end the Exec= line entirely and let the remainder be parsed as further desktop-entry keys (the original guard, kept).

Same injection class the XML path already handles via xml_escape; this is the desktop-entry grammar’s version of it.