Typer/Click CLI Completion: Bypass shellingham

Python CLIs built on [Typer] (and [Click] under it) ship --install-completion and --show-completion, which rely on shellingham to detect the parent shell. shellingham walks the parent process tree (/proc/$PPID/comm-style), not $SHELL. When the parent is anything other than a known shell, detection raises ShellDetectionFailure and Typer prints:

Shell None is not supported.

Setting $SHELL=/bin/zsh does not help. shellingham ignores the env var by design — the point is to detect the real running shell, not to trust what the environment claims.

When the failure mode bites