Function spawn_streaming 

pub fn spawn_streaming<F>(
    program: PathBuf,
    args: Vec<String>,
    env: Vec<(String, String)>,
    cwd: PathBuf,
    run_id: String,
    callback: F,
) -> Result<ProcessHandle, StreamError>
where
    F: FnMut(ProcessEvent) + Send + Sync + Clone + 'static,

Spawn an arbitrary streaming child process — the generic engine behind every process-backed harness (bob, Claude Code, Codex).

Pipes stdout/stderr line-by-line through callback using the raw ProcessEvent vocabulary (Started / Stdout / Stderr / Error / Exited). env supplies per-harness secrets (each harness’s API-key var, or none for self-authenticating CLIs). PATH is augmented so Node-based CLIs find node. Returns a ProcessHandle for cancellation.

callback is invoked from three threads (stdout reader, stderr reader, exit watcher); the Clone bound lets us hand a copy to each. run_id is opaque — the caller chooses it and uses it to correlate events with the handle.

use cli_stream::{spawn_streaming, ProcessEvent};
use std::path::PathBuf;

let handle = spawn_streaming(
    PathBuf::from("echo"),
    vec!["hello".to_owned()],
    Vec::new(),                      // extra env vars (key, value)
    std::env::current_dir().unwrap(),
    "run-1".to_owned(),              // your correlation id
    |event| match event {
        ProcessEvent::Stdout { line, .. } => println!("{line}"),
        ProcessEvent::Exited { exit_code, .. } => eprintln!("exit {exit_code:?}"),
        _ => {}
    },
)?;
// `handle.cancel()` stops it early; dropping the handle does not.
let _ = handle;