Native Termux and proot Boundaries

Purpose

Stop packages, paths, and assumptions from leaking between native Termux and a proot distro, and pick the side that should own a given task.

When to use

• A command behaves differently in a proot Ubuntu or Debian than in native Termux.
• An Android-facing feature (Termux:API, storage links) is missing inside proot.
• A prebuilt glibc binary or wheel is needed.
• Before installing, backing up, resetting, or removing a distro.

When NOT to use

• The shell is clearly native Termux and the error is a plain pkg or build error: use package-troubleshooting or python-native-build.
• As a reason to move work into proot by default. Proot costs storage, I/O speed, and ptrace overhead.

Preconditions

Run sh scripts/detect-boundary.sh. Treat a prompt label as unreliable; use $PREFIX, tracer_pid, os_release_id, and the installed distro list as evidence.