Function spawn_with_memory_limit 

pub fn spawn_with_memory_limit(cmd: &mut Command) -> Result<Child>

Spawns a command with a virtual memory limit via setrlimit(RLIMIT_AS).

On Linux, applies the limit in a pre_exec hook before the child process starts. On non-Linux platforms, falls back to an unlimited spawn. The limit is read from SQLITE_GRAPHRAG_SUBPROCESS_MEMORY_LIMIT_MB (default: 4096 MiB).