The build context is the repo root, not this directory (the image needs backend/, electron/, frontend/ and backend/requirements.lock). amd64 only, see the renderer section:

docker build --platform linux/amd64 -f openswarm-runner/Dockerfile -t openswarm-runner .

Nothing has to be built on the host first: the frontend bundle and the shell's node modules are built in their own stages inside the image.

Run

The container is told everything it needs by one JSON run spec in OPENSWARM_RUN_SPEC (or a path in OPENSWARM_RUN_SPEC_FILE). See runner/run_spec.py for the typed shape.

{
  "run_id": "cr_01J...",
  "workflow": { "id": "wf_1", "title": "Daily digest", "model": "opus-5",
                "steps": [{ "text": "summarize my inbox" }] },
  "credentials": [
    { "provider": "claude", "auth_type": "oauth",
      "access_token": "<already refreshed by the control plane>",
      "expires_at": "2026-07-31T20:00:00Z" }
  ],
  "callback": { "url": "https://api.openswarm.com/api/cloud-runs/cr_01J.../report",
                "token": "<two-party runner token, not a user credential>" },
  "max_run_seconds": 1800,
  "needs_browser": true
}

Exit codes: 0 ok, 1 runner crash, 2 bad spec, 3 credential expired on arrival, 4 backend never came up, 5 workflow failed, 6 wall-clock cap hit, 7 no Electron window ever registered.

Files the run makes

/data/workspace is the agent's working directory and the only path whose contents survive. It is seeded as default_folder before the backend boots, and the agent is told in its system prompt that files saved there come back and everything else is destroyed.

After the workflow reaches a terminal state (including a timeout, so partial work still lands) the runner walks that directory and POSTs each file to callback.artifacts_url, then sends the terminal report. That order is load-bearing: the per-run callback token is refused once the run is closed, so uploading afterwards would be rejected.

Caps, applied in the runner AND again at the control plane, which is the one that counts:

Limit	Value
One file	20 MB
One run, all files	50 MB
Files per run	40

Nothing is ever truncated. A file past a cap is not sent and instead arrives as a row in the report's files[] carrying a written reason, so the user reads "your 512 MB render could not be sent" rather than finding a 20 MB fragment. .git, node_modules, __pycache__, .venv, .claude and the usual caches are skipped, and symlinks are never followed.

Skills and connected apps

skills[] in the run spec is written to ~/.claude/skills/<id>/ before boot. This is not a nicety: the backend registers the Skill tool only when at least one non-built-in skill exists on disk, so a container without them has no Skill tool at all and answers from general knowledge in the same confident voice it would use with the real thing.

unavailable_mcp_servers[] is names only. The user's MCP credentials (Slack session cookies, Notion and GitHub access tokens, Google refresh tokens) never leave their machine, so the names go up purely so the run's system prompt can tell the agent which apps exist and are out of reach. McpServerNote forbids extra fields, so there is no shape a secret could travel in.

What the image carries for the App Builder

node, npm and npx, plus the App Builder template's node_modules pre-installed at the digest path bundled_extracted_modules() probes. Without npm, CreateApp scaffolded an app that could never install, build or serve; without the baked cache, the first CreateApp in a run would pay a cold registry install. git also carries a system identity (/etc/gitconfig), so a workflow that commits does not die on "Author identity unknown".

The renderer

OpenSwarm's browser tier is not an HTTP client. Element serialization and every click, type and scroll live in frontend/src/shared/browserCommandHandler.ts and drive a live Electron <webview>; the backend only relays commands over the dashboard WebSocket. So the container runs the real desktop shell, unmodified, on a virtual display:

Xvfb :99 -> Electron (ELECTRON_DEV=1, OPENSWARM_DEV_URL=<bundle>#/dashboard/cloud-run)
         -> registers on /ws/dashboard -> browser tools are live

ELECTRON_DEV=1 is the same path bash run.sh uses: the shell attaches to the backend already running here instead of spawning a second one. The bundle is served off loopback on :4173, the same port the packaged app prefers, and deep-linked at the run's one dashboard so no human has to click anything.

Three things follow from this and are worth knowing before you touch it:

amd64 only. CastLabs (whose Electron the desktop app ships) publishes no linux-arm64 build. Running a different Electron in the cloud than users run on their laptops would quietly undo the point of the image, so the build refuses other arches.
--no-sandbox. Chromium's setuid sandbox needs a root-owned binary and its namespace sandbox needs unprivileged user namespaces; a non-root container under Docker's default seccomp has neither. The wall this run relies on is the Firecracker VM around the whole container, not Chromium's own layer. The flag lives in a named constant in runner/renderer_process.py rather than inside a launch string, on purpose.
needs_browser: false skips it. Boot costs roughly 15s and ~500MB of the run's memory, so a workflow that never opens a page can opt out. Default is on: parity is the reason this image exists, and opting out should be the thing you have to say.

If Electron starts but no window ever registers, the run fails (exit 7) rather than proceeding without a browser. A browser workflow that silently ran blind produces a confident wrong answer, which is worse than no answer.

Parity with a local run, and the one gap we accept

A cloud run boots the same Electron shell, the same backend and the same browser code path as a laptop does, so browser steps behave the same in both places.

How well, exactly, is not yet measured on Linux. The 19-row matrix scores 19/19 on macOS and the result file is kept. Nobody has scored the Linux-under-Xvfb side row by row; a code comment in openswarm-cloud/src/workflows/runnerCapabilities.ts used to claim 18/19 with no artifact behind it. Run parity/stage.py on a real runner machine before quoting any cloud number. It needs a native amd64 host: under qemu on an arm64 Mac, Electron never registers and the harness exits 7 without scoring anything.

One row is expected to fail there and is not going to be fixed: obstacle.bot_wall, because the run comes from a datacenter IP. Separately, one whole capability is refused at create time rather than failed at 3am:

A workflow that needs an account you are already signed into. Every run gets a fresh browser profile in a throwaway container. There is no keychain, no cookie jar, and nobody there to type a password or clear a 2FA prompt. Copying a logged-in session up would mean shipping the user's live cookies to a machine we destroy minutes later, which is a worse trade than refusing.

This is declared, not implied: signed_in_browser is deliberately absent from RUNNER_CAPABILITIES in openswarm-cloud/src/workflows/runnerCapabilities.ts, and checkRunnerCapabilities turns it into a refusal that names the workaround ("run it on your own machine"). tests/runner-capabilities.test.ts asserts the flag stays off, so nobody can quietly flip it without reading this.

Everything else in that matrix is a capability flag that can flip when the container learns the trick. browser already did: it was refused until Electron under Xvfb landed, and flipping the one flag unblocked every browser workflow with no other edit.

The credential rule

A providerConnections[] entry this runner writes never contains a refreshToken. 9Router's refresh dispatcher bails on if (!b || !b.refreshToken) return null, so omitting the field is what makes the container incapable of rotating the user's grant. If it ever rotated, the user's laptop would be left replaying a dead token and the provider would revoke the whole grant family.

Two independent walls enforce it, and a third makes a leak require deleting the code that builds the entry:

ProviderCredential forbids extra fields, so a spec carrying refreshToken fails validation before the backend boots.
assert_no_refresh_token re-reads the assembled db payload just before the write.
router_connection assembles the entry from a fixed key list, never a passthrough.

All three live in runner/seed/router_credentials.py.

An access token that arrives expired fails the run (exit 3). The runner never refreshes.

Test

PYTHONPATH=.:openswarm-runner backend/.venv/bin/python3 -m pytest openswarm-runner/tests -q

The Electron boot itself needs Linux and a display, so the tests pin the contract around it (the deep link, the bundle check, the three ways "no window" ends) rather than the boot. Proving the browser tier actually behaves means running a real page in both places and comparing; see the parity matrix in the cloud-browser work notes.

Deploy

Not deployed. fly.toml is written but never applied; read its header first, the app has to be created onto its own isolated private network by hand before any deploy.