fix(sandbox-vercel): forward credentials when resuming sessions

[doneumark]

Background

@ai-sdk/sandbox-vercel forwards Vercel Sandbox create settings into Sandbox.create() and Sandbox.getOrCreate(), including access-token credentials (token, teamId, projectId). However, resumeSession() reattaches by calling Sandbox.get({ name }) without forwarding those settings.

In non-Vercel environments that use access-token auth, first session creation succeeds but a later agent.createSession({ sessionId, resumeFrom }) can fail when the provider tries to resume the named sandbox and @vercel/sandbox falls back to OIDC:

Could not get credentials from OIDC context.
Please link your Vercel project using `npx vercel link`.
Then, pull an initial OIDC token with `npx vercel env pull`
and retry.

Summary

• Forward reusable sandbox lookup credentials into Sandbox.get() from resumeSession().
• Forward the same lookup credentials when polling for a template snapshot after Sandbox.getOrCreate().
• Add a regression test asserting named session resume forwards token, teamId, projectId, and signal.
• Add a patch changeset for @ai-sdk/sandbox-vercel.

Manual Verification

I verified the failure mode against the installed package source by reproducing the code path where createSession() uses access-token settings but resumeSession() calls Sandbox.get({ name }) without them. The updated unit test covers the credential forwarding needed for that path.

Automated checks run locally:

pnpm --filter @ai-sdk/provider-utils build
pnpm --filter @ai-sdk/sandbox-vercel test
pnpm --filter @ai-sdk/sandbox-vercel type-check
pnpm --filter @ai-sdk/sandbox-vercel build
pnpm exec ultracite fix packages/sandbox-vercel/src/vercel-sandbox.ts packages/sandbox-vercel/src/vercel-sandbox.test.ts .changeset/tidy-sandboxes-resume.md

Note: pnpm --filter @ai-sdk/harness build was also attempted after building @ai-sdk/provider-utils, but its DTS build failed resolving @ai-sdk/provider-utils declarations. The focused @ai-sdk/sandbox-vercel tests/typecheck/build pass after dependencies are installed.

Checklist

• All commits are signed (PRs with unsigned commits cannot be merged)
• Tests have been added / updated (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features - run pnpm changeset in the project root)
• I have reviewed this pull request (self-review)

Related Issues

No existing issue found when searching vercel/ai and vercel/sandbox for sandbox-vercel resumeSession Sandbox.get credentials.

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