How it works

What happens between hi <target> and the prompt, end to end. What a target is trusted with is SECURITY.md; every setting named here is a row in SETTINGS.md.

1. hi.sh runs on the client, tars say-hi/, and sends it to the target, which unpacks it into a /tmp directory. $_HI_PAYLOAD at the top of hi.sh is the allow list — no .git, scripts/, tests/, docs/, or CI. Your overlay follows in a second, much smaller archive, unpacked into the same config/: a tree default your overlay replaces outright (colors, packages) stays home, so one copy rides (HI.41), and your aliases.sh stays additive, since hi’s own are common/aliases.sh.
2. Both are base64-armored inside one script written over the stdin of an ssh connection the session then reuses — not argv, which Linux caps at 128KB per argument however big ARG_MAX says (HI.19). Every shell file is comment-stripped on the way in (about 40% of it).
3. That script is the size hi prints on connect and what README’s payload badge measures, an overlay only adding to it: the per-session wire cost, not what a release downloads (scripts/ and the docs ship in a package, never over the wire).
4. On the target, load.sh prints the header, writes hi’s per-shell rc files into a scratch directory of its own (HI.46) - never the target’s own login files - and drops you into your login shell when hi styles it (bash, zsh, fish), else the best the target has of hi’s shell tree (fish > zsh > bash > dash > ash > sh; with no bash at all, the same list without bash).
5. On exit, the session’s EXIT trap removes the /tmp directory and the scratch rc directory. bash runs it on the hangup a dropped connection sends too, so that cleans up the same way, with nothing left to reconnect to. Two ways to survive a drop, both in INTEGRATIONS.md: hi --mux <target> runs the connect inside a multiplexer on the client, and hi --keep <target> runs the session inside one on the target, where the tree stays until that session closes or times out.
6. hi <target> 'some command' runs the command inside that same session - hi’s aliases and environment, a pty when your stdin is one - and prints only its output; a plain, pty-free remote command is ssh’s job.

The bootstrap is plain POSIX sh, so a target with no bash still gets a session in the best plain shell it has, aliases loaded. Every ssh target gets the tree shipped to it, whether or not that machine has a say-hi of its own: an install there is for that machine’s own shells, and a session neither reads nor touches it. hi --doctor prints the wire size and the unpacked size.