vercel() sandbox backend ignores the runtime option and always runs vercel/eve:latest

[z3thon]

Summary

vercel() sandbox backend ignores the runtime option and always runs vercel/eve:latest.

When a sandbox is defined with defineSandbox({ backend: vercel({ runtime: "python3.13" }) }), the requested runtime is silently dropped. The Vercel binding hardcodes the base image to vercel/eve:latest and does not forward runtime to the @vercel/sandbox SDK create() call, so the sandbox never runs the requested runtime — with no error or warning.

Version

eve 0.13.1

Where (from the published dist)

• dist/src/execution/sandbox/bindings/vercel-create-sdk.js sets __image: VERCEL_EVE_SANDBOX_IMAGE (= "vercel/eve:latest") on the SDK create.
• runtime does not appear in that create path (it is not forwarded from vercel({ runtime }) to the SDK).

Reproduce

1. defineSandbox({ backend: vercel({ runtime: "python3.13" }) }).
2. In a tool: const s = await ctx.getSandbox(); await s.run({ command: "cat /etc/os-release; python3 --version" }).
3. Observed: the base is vercel/eve:latest (currently Ubuntu) with its own bundled Python — NOT the python3.13 runtime that was requested.

Impact

1. Silent option drop — runtime is accepted by vercel() but ignored at create time; no error/warn. A footgun: callers believe they're on the runtime they asked for.
2. Wrong base for native-toolchain workloads — anything that depends on the requested runtime's base (packages, package manager, Python version) gets vercel/eve:latest instead. (Concretely: a bootstrap that assumed the python3.13 base's tooling broke because vercel/eve:latest lacks bzip2.)
3. Reproducibility — vercel/eve:latest is a mutable tag with no way to pin a digest, so the sandbox base can drift between deploys (we observed it as a different distro than expected). For workloads that must reproduce results exactly, an unpinnable base is a real problem.

Ask

Either honor the runtime option in the Vercel binding, or document explicitly that vercel() always uses vercel/eve:latest and expose a way to (a) select the runtime and (b) pin the base image by digest for reproducible builds.