Fork a sandbox
Do the expensive setup once, then fork the live container into independent children.
sb.fork() copies a running container — filesystem, installed packages, everything currently on
disk — into a new sandbox that runs independently. Pay a slow npm ci or model download once on
a base sandbox, then fork it N ways to parallelize the work that follows.
This workflow builds a shared baseline, forks it twice, has each child modify the same file, and shows that neither child can see the other's changes.
Not connected
createSandboxexecforkdeleteSandbox~1 min
Connect to a sandbox server above to run this.
What just happened
- The base sandbox wrote
/work/base.txt— stand-in for expensive setup. sb.fork("child-a")andsb.fork("child-b")each produced a full, independent copy of the base container at that moment.- Child A appended
"A was here"; child B appended"B was here". The final stepcats the file in each: A's copy has only A's line, B's has only B's. The fork is a copy, not a shared mount.
The hosted endpoint caps total sandboxes at 3 (base + 2 forks = the whole budget). If a fork step reports a capacity error, another reader is using the endpoint — retry in a moment, or run locally.
See also the Parallel Test Shards cookbook.