Local implementation of the [`@deepseek-ai/dsh-sandbox`](../sandbox/) seam: wraps a caller's argv in a platform confinement runner. Selection is BY PLATFORM, resolved once and cached: each platform names its runner chain, a chain of one is selected directly (probing arbitrates between candidates — a sole candidate leaves nothing to arbitrate), and a chain of several is probed functionally in preference order. Linux: [`bwrap`](https://github.com/containers/bubblewrap) when its probe passes, else the [`landlock-run`](https://www.npmjs.com/package/node-addon-landlock-run) Landlock launcher (kernel confinement that needs no userns/mount privileges — see the [sandbox RFC](../../../docs/rfc/implemented/feature/2026-07-06-sandbox.md) for the prebuilt-binary decision and profile-parity notes); darwin: `sandbox-exec` speaking a Seatbelt (SBPL) profile, unprobed. A platform with no chain means `confine()` FAILS CLOSED with the seam's structured `SANDBOX_UNAVAILABLE` error (win32 today: a reserved, deliberately empty chain awaiting an AppContainer-family runner); an unprobed runner that turns out unusable fails closed at EXECUTION instead — it refuses to run the command, and every wrap's `runnerFailureSignatures` let the consumer classify that as a sandbox failure rather than a task failure. Never a silent unconfined passthrough on any path.
Policy is per call; the provider stores only the mechanism and cached runner verdict. Each wrap reports enforcement completeness plus backend-specific denial and runner-failure signatures. `runnerCommand` is an operator assertion of a bwrap-shaped runner and skips probes, but missing or unexecutable commands still fail closed at execution. Because its mechanism is unknown, it carries both Linux denial dialects. `probeTimeoutMs` bounds functional probes. The [sandbox RFC](../../../docs/rfc/implemented/feature/2026-07-06-sandbox.md) owns selection and failure semantics.
The Seatbelt profile is allow-default with `(deny file-write*)` plus write allow-lists, so exactly the mode's promised file effects are governed: `read-only` grants the `/dev/null` literal alone; `workspace-write` adds the workspace root, `/tmp`, and the per-user darwin temp dir (`os.tmpdir()` — the platform's real temp area for mkstemp-family tools), every root canonicalized because Seatbelt matches resolved paths (`/tmp` IS `/private/tmp`). Apple marks the `sandbox-exec` CLI deprecated but ships it on every macOS; the functional probe is what fails closed if that ever changes.
The Landlock launcher comes from the npm package family [`node-addon-landlock-run`](https://www.npmjs.com/package/node-addon-landlock-run) — an entry package (this package's one runtime dependency) plus per-platform binary packages selected by npm's `os`/`cpu` fields, built and released from [its own repository](https://github.com/deepseek-harness/node-addon-landlock-run). The entry package owns the launcher's CLI contract: `launcherPath()` resolution (a host with no platform package yields a never-existing path whose probe fails exactly like an unenforcing kernel), the functional `probe()`, and `grantArgs()` flag spelling — versioned together with the binary, so probe-report parsing can never drift against it. This provider keeps only the policy side: the mode → grants mapping (`landlockProfileArgs`) and the ladder. The consumer path is rehearsed by `tests/packed-install.e2e.ts`: pack THIS package's closure, install into a throwaway consumer with the launcher family coming from the registry, assert the installed binary executable (a stripped mode bit must not masquerade as a non-enforcing kernel), and confine through it under plain `node`.
Every rung has its keyless world-proof (`tests/bwrap.e2e.ts`, `tests/landlock.e2e.ts`, `tests/seatbelt.e2e.ts`), each self-skipping where its runner is absent; CI's `sandbox-e2e` matrix runs all of them against real kernels (bwrap plus one Landlock leg per architecture on Linux, Seatbelt on macOS) and fails on a silent all-skip.
Consumers: [`@deepseek-ai/dsh-bash-sandbox`](../../bash/bash-sandbox/); see [`examples/sandbox-acp-agent`](../../../examples/sandbox-acp-agent/) for the runnable composition.
