[earakely-scale]

What and why

Sandbox providers now declare whether their sandboxes' exposed ports carry WebSockets, and a computer with a website browser among its apps refuses a provider that doesn't. A website browser's CDP address is a WebSocket. On a provider whose tunnel doesn't carry one, the deploy succeeded, and then every CDP client failed to connect. This is FD-4950 (M8.3). Its outcome and two decisions are recorded there.

The declaration (decision 2): WEBSOCKETS: ClassVar[bool] = False in SandboxProvider's "what it declares" block, beside PRIVATE_NETWORK.

Where it's on (decision 1), wherever there's evidence, by one rule:

Provider	Evidence
local	our own WebSocket tests (M8.6, #500)
smol_vm, lume	VMs on this machine, their ports reached with no tunnel
modal, modal_vm	Modal's tunnels; modal_vm uses the same ones
boxd, sail_vm, tenki, agent37	their READMEs say their tunnels carry WebSocket

It stays off for e2b, tensorlake, vercel, coreweave, daytona and boat until M8.25 tests each live. agent37 isn't in M8.25's list, probably because it was added after the Nov 1 plan.

The checks. A computer env serves a website browser when one of its composed apps has browser = true in its stored declaration. That's chromium today, alone as a browser computer or as an app in a desktop. ComputerEnv.serves_website_browser() reads it, and two places check it:

• Preflight: ComputerEnv.deploy_refusal, beside the native-arch and network-policy checks, refuses when no link that runs the env natively carries WebSockets, and names them. The network policy is checked against the same links, so a chain where one link carries WebSockets and another enforces the network is refused too. That check runs when a task is saved. At deploy, as for the native-arch and network checks, the per-link check below refuses before anything boots.
• Deploy: the computer provider's _boot raises on a link without WebSockets, so a chain moves on to the next link, the same way it moves past a link that runs none of the env's builds natively.

Docs: the root AGENTS.md and the providers' AGENTS.md list the new declaration.

Not in this PR:

• the live per-provider checks (M8.25);
• multi envs with a browser (M8.13);
• the playwright-mcp website browser, which agents reach through MCP, never CDP.

How it was tested

• ruff check: clean.

• Unit tests:

  • Declarations: the provider capabilities table gains a WEBSOCKETS column, and a provider that declares nothing doesn't carry WebSockets.
  • Preflight: a computer env with chromium among its apps passes preflight on the local provider. With its WEBSOCKETS off, saving the task is refused: "LocalSandboxProvider carries no WebSockets, which its website browser's CDP address needs".
  • Deploy: on a real ChainedSandboxProvider whose first link is the local provider with WEBSOCKETS off, the deploy skips that link and boots on the second.
  • Mixed chain: a chain where one link carries WebSockets and another enforces the network is refused at save (Greptile's case).

  The computer, app, disk, sandbox provider and bundle preflight tests: 1997 passed, 7 skipped. CI runs the full unit tier.

• Dry run: agent-env run agents --task browser-use-smoke --dry-run on local, e2b, and a chain of e2b then local. The run writes chromium itself, so its deploy_env isn't preflighted in a dry run, and the refusal fires at deploy instead, before anything boots.

• E2e on agent-environments-admin VMs, amd64 and arm64, at e515b611:

  • Setup: agentenv's real chromium, composed and stored as a browser computer, and a provider registered through a config file ([sandbox.providers.nows] impl = …): the local provider with WEBSOCKETS off.
  • Save: a task deploying it on nows is refused: "computer env '…/chromium': NoWebSocketsProvider carries no WebSockets, which its website browser's CDP address needs".
  • Deploy on nows alone: refused before any container starts. The container count was the same before and after.
  • Deploy on nows,local: the nows attempt is logged as failed for that reason, the deploy boots on local, and a CDP client answers Browser.getVersion (Chrome/156) over the WebSocket.
  • Regression on local: browser_computer_test.py and browser_gateway_test.py 11/11 on amd64, and 8/8 on arm64 without the 3 echo-agent tests, which need qemu there.
  • The harness is a scratch script, not committed.

• Not tested live: a chain that skips a real remote provider without WebSockets. That needs one that also runs the browser natively, which means credentials. M8.25's live checks are where each remote provider gets tested.

🤖 Generated with Claude Code

Confidence Score: 5/5

The PR appears safe to merge; the previous preflight gap is fixed.

Summary

Adds WEBSOCKETS declarations and refuses browser computers on providers without that support.

• Browser computers use only providers that declare WebSocket support.

_{Reviews (2) · Last reviewed commit: "fix(computer): a deploy's network is che..." · Reviewed by Greptile}