Vercel Sandbox creation now returns a ready sandbox

A new Vercel Sandbox is now ready to run commands and read or write files when creation completes.

Sandbox.create() now resolves only after snapshot restoration completes, so the first command or file operation no longer waits for it. Startup errors also reject Sandbox.create() instead of surfacing during that operation.

Snapshot restoration time now counts toward creation instead of the first operation. Creation is about 50 ms longer at p50, with a larger increase possible for uncached snapshots. The total time through the first operation remains the same.

This change applies automatically, with no SDK upgrade or configuration changes required. See the Sandbox.create() documentation for details.