Runloop sandbox backend¶

Bernstein's runloop sandbox backend talks to the Runloop REST API (https://runloop.ai) and conforms to the SandboxBackend protocol.

Module¶

src/bernstein/core/sandbox/backends/runloop.py - class RunloopSandboxBackend, registered under the name runloop in bernstein.core.sandbox.registry.

Environment variables¶

Variable	Required	Purpose
`RUNLOOP_API_KEY`	yes	Bearer token from the Runloop Dashboard.
`RUNLOOP_API_URL`	no	API root override. Defaults to `https://api.runloop.ai/v1`.
`RUNLOOP_PROJECT_ID`	no	Default project id forwarded as `project_id` on devbox creation.

Capabilities¶

FILE_RW, EXEC, NETWORK, SNAPSHOT. Runloop devboxes can be snapshotted via POST /devboxes/{id}/snapshot_disk and resumed via POST /devboxes with snapshot_id.

Selecting the backend¶

sandbox:
  backend: runloop
  options:
    blueprint: runloop/blueprint-python
    project_id: prj-bernstein

Honest limitations¶

Synchronous exec only. This backend uses POST /devboxes/{id}/execute_sync which buffers stdout/stderr until the command exits. Long-running interactive workloads should use Runloop's WebSocket exec channel directly; Bernstein's SandboxSession.exec contract is unary-response.
No stdin injection. Passing stdin= raises NotImplementedError.

Integration tests¶

Live integration tests are gated by CI_RUNLOOP_TEST=1 plus RUNLOOP_API_KEY. Without them the test in tests/integration/sandbox/test_runloop_backend.py skips cleanly.