Struct SubshellSnapshot 

pub struct SubshellSnapshot {
    pub variables: HashMap<String, String>,
    pub arrays: HashMap<String, Vec<String>>,
    pub assoc_arrays: HashMap<String, IndexMap<String, String>>,
    pub positional_params: Vec<String>,
    pub env_vars: HashMap<String, String>,
    pub cwd: Option<PathBuf>,
    pub umask: u32,
    pub traps: HashMap<String, String>,
}

Snapshot of subshell-isolated state. Captured at ( entry, restored at ) exit. zsh subshell semantics: assignments inside (…) don’t leak to the outer scope — and that includes export. zsh forks a child for the subshell so the child’s env::set_var dies with the child; without a fork (zshrs runs subshells in-process for perf), we snapshot+restore the OS env table around the subshell. Otherwise (export y=v) would leak y to the parent shell, breaking every script that uses a subshell to scope an env override.

Fields

variables: HashMap<String, String>

arrays: HashMap<String, Vec<String>>

assoc_arrays: HashMap<String, IndexMap<String, String>>

positional_params: Vec<String>

env_vars: HashMap<String, String>

cwd: Option<PathBuf>

Process working directory at subshell entry. cd inside the subshell shouldn’t leak to the parent; we restore on End.

umask: u32

File-creation mask at subshell entry. zsh forks for (...) so umask set inside dies with the child; we run subshells in process so we must restore the mask on End. Otherwise umask 022; (umask 077); umask shows 077 in the parent.

traps: HashMap<String, String>

Parent’s traps at subshell entry. zsh’s (trap "echo X" EXIT; true) runs the trap when the subshell exits — BEFORE the parent continues. Without this snapshot, the trap inherited from parent would fire, OR a trap set inside the subshell would leak to the parent’s process exit. Restored on subshell_end after the subshell’s own EXIT trap (if any) has fired.