feat(vercel-sandbox): fix resume race-condition

[marc-vercel]

Fix resume race-condition: ensure that when we call withResume multiple times, we only have one request in-fight.

For example, we were having a race condition and created two active sessions:

❯ sandbox create
  ✅ Sandbox coral-sour-iguana-jroMkL created.
     │ team: marc-codina-enhanced-vtest314
     ╰ project: my-sandbox-app
  ❯ sandbox stop coral-sour-iguana-jroMkL
  ✔ Stopping sandbox coral-sour-iguana-jroMkL
  ❯ sandbox ssh coral-sour-iguana-jroMkL
  $ sh
  ▲ /vercel/sandbox/ sandbox session list coral-sour-iguana-jroMkL
  sh: sandbox: command not found
  ▲ /vercel/sandbox/ sandbox session list coral-sour-iguana-jro^CL
  ▲ /vercel/sandbox/ exit
  exit

  ╰▶ connection to ▲ coral-sour-iguana-jroMkL closed.
  ❯ sandbox sessions list coral-sour-iguana-jroMkL
  ID                                 STATUS    CREATED        MEMORY   VCPUS   RUNTIME   TIMEOUT        DURATION
  sbx_1SMyrcBI54UQSPyRB9wPF6PCqOx2   running   1 minute ago   4096     2       node24    in 4 minutes   -
  sbx_OF2yUnDjZyiYhOaA90JKLu3rUa6c   running   1 minute ago   4096     2       node24    in 4 minutes   -
  sbx_UidxVjezS5n7vB8fc8WkxgtVQgyE   stopped   1 minute ago   4096     2       node24    in 4 minutes   12.029s

Root cause of the race-condition:

When doing a sandbox ssh, we run two operations concurrently via Promise.race:

• checkIfServerInstalled() → calls sandbox.runCommand()
• installServerBinary() → calls sandbox.writeFiles()

[vercel]

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Project	Deployment	Actions	Updated (UTC)
sandbox-sdk	Ready	Preview	Mar 17, 2026 2:01pm