The rule that the shell emulator takes POSIX quoting on every platform was
only observable on Windows. Both stacks gated it behind a platform check
that is constant for a given run, so a Linux or macOS job could not tell
`windows && !shell_emulator` from `windows` alone.
Take the platform as a value in `parsed_by_windows_shell` and give
`build_command` the shell family it should quote for. Both quoting branches
and the emulator rule are now asserted on any host, which also retires the
`build_command` case that was ignored on Windows and leaves the JSON branch
covered for the first time off Windows.
Mock `is-windows` in a lifecycle test so the same rule is exercised through
`runLifecycleHook` on any host. Each assertion was confirmed to fail when
its half of the rule is removed.
Related to pnpm/pnpm#14548