Function stable_target 

pub fn stable_target() -> Result<PathBuf, String>

What the login entry should run: something that survives updates (SPEC_START_WITH_OS_2026_09_25.md §3.1), not this process’s own path.

1. AGENTMUX_STABLE_EXE as captured by take_stable_exe_env: the AppImage file (set by AppRun), or the deb/rpm/tarball wrapper that sets the LD_LIBRARY_PATH the raw launcher cannot run without.
2. current_exe(): Windows and macOS installs, portable and dev builds.