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.

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.

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.