feat(ai-sandbox-upstash-box): add Upstash Box sandbox provider

[alitariksahin]

Closes #898

What

Adds @tanstack/ai-sandbox-upstash-box, a sandbox provider that runs harness adapters inside isolated Upstash Box cloud sandboxes through the uniform SandboxHandle — alongside Docker / Daytona / Vercel / Cloudflare / Sprites.

How

Built on the Daytona provider as the closest reference:

• fs — Box's native file API for read/write/list; shell (exec) for mkdir/remove/rename/exists. Virtual /workspace ↔ Box /workspace/home (Box.WORKSPACE) path mapping; list() returns paths in the caller's virtual namespace.
• exec / spawn — shell-wrap cwd + env; env exports go before cd so a failed cd (&&-gated) doesn't run the command. spawn() streams stdout over exec.stream; wait() resolves on the exit chunk; kill() aborts via an AbortController that unblocks a silent stream. writableStdin: false (Daytona parity).
• ports — getPublicURL, mapping bearer/basic auth to channel headers.
• snapshots — native box.snapshot() / Box.fromSnapshot(), plus provider.restoreSnapshot().
• capabilities — backgroundProcesses: true, snapshots: true, durableFilesystem: true; writableStdin/networkPolicy/fork false. Best-effort signal.throwIfAborted() pre-flight on create/resume/restoreSnapshot/destroy/exec/spawn (the Box SDK can't cancel in-flight calls).

Also updates the central provider-list table in @tanstack/ai-sandbox's README and adds a changeset.

Test plan

• pnpm --filter @tanstack/ai-sandbox-upstash-box test:types — ✅
• pnpm --filter @tanstack/ai-sandbox-upstash-box test:eslint — ✅
• pnpm --filter @tanstack/ai-sandbox-upstash-box test:build (publint) — ✅
• pnpm --filter @tanstack/ai-sandbox-upstash-box build — ✅
• pnpm --filter @tanstack/ai-sandbox-upstash-box test:lib — ✅ 18 tests
  • Unit tests run against a mocked Box (path mapping, cwd/env wrapping, spawn streaming + silent-stream kill(), public-URL mapping, capability flags).
  • Gated integration tests (describe.skipIf(!UPSTASH_BOX_API_KEY)) run against live Upstash Box: create → exec → text/binary fs round-trip → streamed spawn → destroy, and snapshot → restoreSnapshot → verify file survives.
• pnpm test:sherif / pnpm test:knip — ✅

Sandbox providers aren't part of the E2E harness matrix (testing/e2e/feature-support.ts covers chat/streaming adapters); this follows the Daytona/Docker/Vercel convention of gated integration tests in the package's own tests/.

Draft / blocked on

Opened as a draft because pnpm-lock.yaml still needs the @upstash/box entry. The lockfile couldn't be regenerated in my dev environment (registry/CDN metadata issues unrelated to this change). Will push the lockfile update to make CI green before marking ready for review.

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[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	@​upstash/​box@​0.5.1

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[AlemTuzlak]

@alitariksahin this is in draft, is this still relevant?

[AlemTuzlak]

@alitariksahin would you mind pushing this over the finish line so we can get it merged?

[alitariksahin]

@AlemTuzlak I will give it a final check, and get the sdk up to date today.