Vercel demo — Self-Hosted Sandboxes

Same webhook → drain-queue → per-session runner shape as the Modal, Daytona, and Cloudflare demos, but the runner is a Vercel Sandbox running the TS EnvironmentWorker.handleItem() with the SDK's betaAgentToolset20260401() against the sandbox's real filesystem (bash / read / write / edit / glob / grep).

The webhook function (api/webhook.ts) is a wake-up signal only. It verifies the Standard Webhooks signature with client.beta.webhooks.unwrap(), drains work.poll() until empty (capped at 25), and per item: acks, creates a Vercel Sandbox, uploads runner/runner.mjs, and starts it detached. A bad work item is logged and skipped — it stays un-acked and reclaims on the next webhook, so it can't wedge the rest of the queue.

Idle policy is the SDK default: the dispatcher exits 60s after session.status_idle with stop_reason: end_turn; any other event — including requires_action idle, where the agent is blocked on the sandbox — resets the clock.

No org API key anywhere: the webhook polls with the environment key, and the runner authenticates with that same environment key — the single credential for both the control plane and the per-session calls.

Files

• api/webhook.ts — Vercel Function: verify sig → drain → spawn sandbox per item.
• runner/runner.mjs — runs inside the sandbox: EnvironmentWorker.handleItem() — builds the per-session AgentToolContext, downloads the agent's skills, runs a SessionToolRunner while heartbeating, force-stops the work item on exit.

Prerequisites

• npm, the Vercel CLI (npm i -g vercel)
• A Vercel project linked (vercel link)
• A registered self-hosted environment + its environment key

Configure

npm install
vercel link
vercel env add ANTHROPIC_WEBHOOK_SECRET   # placeholder for now
vercel env add ANTHROPIC_ENVIRONMENT_ID
vercel env add ANTHROPIC_ENVIRONMENT_KEY

Deploy

vercel deploy --prod

This prints a https://<project>.vercel.app URL. Register https://<project>.vercel.app/api/webhook as a webhook for session.status_run_started in Console (or via the API), copy the issued secret, then update:

vercel env rm ANTHROPIC_WEBHOOK_SECRET production
vercel env add ANTHROPIC_WEBHOOK_SECRET production
vercel deploy --prod

Test

Create a session pointing at your environment id and send it a message:

session = client.beta.sessions.create(agent=agent_id, environment_id=ENVIRONMENT_ID)
client.beta.sessions.events.send(session.id, events=[{"type": "user.message", "content": "ls -la"}])

You should see, in order:

vercel logs <project>.vercel.app
# [webhook] event=session.status_run_started session_id=...
# [webhook] acked work=... session=... sandbox=sbx_... (created)

Sandbox stdout/stderr (the [runner] lines) shows under the project's Observability → Sandboxes tab in the Vercel dashboard.

Notes

• Sandbox.create() + writeFiles() + npm install is ~15–25s before the function responds; vercel.json sets maxDuration: 60. The runner itself is detached. The function also mirrors the runner's first ~30s of output into the function log so it's debuggable from vercel logs without the Sandboxes observability tab.
• Sandbox reuse — Vercel Sandbox has no native tag/label/get-by-name API, so reuse needs external state. If a Vercel KV store is attached (KV_REST_API_URL/KV_REST_API_TOKEN are set), the webhook records session_id → sandbox_id and reuses a running sandbox on the next run_started, calling extendTimeout() so an active session keeps its VM alive across turns. Without KV, every delivery creates a fresh sandbox — SessionToolRunner dedups via seen/answered so a duplicate runner is wasteful, not wrong.
• Working dirs — the webhook creates /mnt/session and /workspace at sandbox start and uses /workspace as the dispatch workdir, matching the Modal/CF demos (skills download to /workspace/skills/<name>/). These are plain ephemeral directories, not persistent volumes — Vercel Sandbox has no volume API. The agent's working tree is gone when the sandbox stops.
• npm install runs inside the sandbox at spawn time so this demo has no build step. To shave ~10s off cold start, pre-bundle runner/runner.mjs with esbuild and upload the bundle instead.