The doctor "can find npm/pi" checks wrap the version command in a POSIX
subshell, `(cmd --version 2>&1 || true)`. Fish treats `( ... )` as command
substitution syntax and forbids it in command position, so every fish user saw
false-negative failures:
fish: command substitutions not allowed in command position
command -v npm && (npm --version 2>&1 || true)
Branch on the detected service shell and emit fish's `begin; ...; end`
grouping for fish, mirroring the existing fish-aware quoting in
serviceShellQuote. Bash and zsh keep the POSIX subshell.
Also guard the `main()` invocation with an ESM main-module check so the CLI
helpers can be imported by tests without side effects, and add a regression
test covering the bash, zsh, and fish command shapes.
