Function render_action 

pub fn render_action(shell: Shell, action: &HookAction) -> String

Render a HookAction into a shell-specific eval-able string. The shell integration script consumes this verbatim via eval (or equivalent).

Why a match instead of a trait

A textbook DIP refactor would introduce a Renderer trait with one impl per shell. We deliberately don’t: there are five shells, the rendering logic for each is a single format!, and the shell list is closed (we wouldn’t add a sixth at runtime). A trait would fragment five trivial format strings across five files without improving testability — the existing per-shell unit tests in this module already exercise each arm independently.