Persist state across runs by name - sandkiln

The default create/stop/gone lifecycle works for one-shot runs, but a lot of real workloads want the same environment back later — a dev environment, a long-lived agent session, anything worth not rebuilding from scratch every time.

The pattern

import { Sandbox } from "sandkiln";

// First run: creates a fresh sandbox named "agent-session-42".
// Every later run: resumes it if it was stopped, or returns it as-is if still live.
const { sandbox, created } = await Sandbox.getOrCreate({ name: "agent-session-42" });

if (created) {
  // set up whatever this environment needs once
}

await sandbox.runCommand("your-agent-loop", []);
await sandbox.stop(); // preserved by default — nothing to do here

from sandkiln import Sandbox

# First run: creates a fresh sandbox named "agent-session-42".
# Every later run: resumes it if it was stopped, or returns it as-is if still live.
sandbox, created = Sandbox.get_or_create(name="agent-session-42")

if created:
    pass  # set up whatever this environment needs once

sandbox.run_command("your-agent-loop", [])
sandbox.stop()  # preserved by default — nothing to do here

kiln sandbox get-or-create --name agent-session-42
# prints the sandbox id and whether it was freshly created

kiln sandbox exec agent-session-42 your-agent-loop
# preserved by default -- nothing to do here

Next time this runs — tomorrow, next week — the exact same getOrCreate({ name: "agent-session-42" }) call resumes the same filesystem state, no explicit snapshot id to track or pass around yourself.

How it works underneath

getOrCreate resolves to one of three outcomes, race-safe under a per-name lock so two concurrent callers for a brand-new name can’t both create a sandbox:

A live sandbox with this name → returned as-is.
A stopped (snapshotted) one → resumed.
Neither → created fresh, given this name.

See Named sandboxes & persistent stop for the full mechanics, and Snapshots, resume, and fork for what “resumed” actually does to the sandbox’s state.

If you need it gone for good

getOrCreate never deletes anything — call sandbox.stop({ keep: false }) explicitly (or kiln sandbox rm --destroy) when you’re genuinely done with that identity and don’t want the snapshot left behind.