Abstract process-sandbox seam. Owns the ctx.sandbox service contract (SandboxProvider) and the confinement vocabulary the harness shares: SandboxMode (read-only / workspace-write / danger-full-access, file effects only), SandboxEnforcement (full / partial, per kernel ABI), SandboxExecutionPolicy (the complete per-call mode + workspace root), SandboxPolicy (its confined subset), and the fail-closed SANDBOX_UNAVAILABLE error. Interface package of the capability-seam split: depends only on cordis (+ the harness error base), never on a backend.

The contract in one line: ctx.sandbox.confine(argv, policy) returns the argv to spawn INSTEAD of your own — wrapped so the process (and everything it spawns) runs confined — plus two facts about the selected backend: the enforcement completeness it achieves and its denial dialect (denialSignatures, the stderr substrings its kernel prints on a denied file effect — what stderr-inferring consumers match instead of a cross-backend union); when no backend is usable it throws rather than passing the argv through unconfined.

Policy rides the call, not the provider: two consumers may confine under different policies at the same instant (bash under read-only while a confined child agent keeps its state directory writable), and an approved escalated retry is just a new call with a wider policy.

Same-world confinement only. A backend shares the host's filesystem and kernel (bwrap, Landlock, Seatbelt); workspaceRoot names the filesystem-canonical real host directory. Workspace identity is resolved before lexical normalization, so a valid cwd containing symlink/.. grants the directory where chdir actually lands rather than an unrelated lexical parent. Containers, microVMs, and remote executors are NOT backends of this seam — they replace whole capability implementations (ctx.bash, ctx.fs) as environment-coherent groups. The boundary and its rationale: the sandbox Agent Note.

Implementations: @deepseek-ai/dsh-sandbox-local (Linux: bwrap, else the per-platform Landlock launcher; macOS: sandbox-exec/Seatbelt). Consumers: @deepseek-ai/dsh-bash-sandbox (wraps ['bash', '-c', command]).

Model Experience

Confinement error, indirectly

What the model sees

Through dsh-bash-sandbox and dsh-tool-bash, failure to enforce a requested mode produces code SANDBOX_UNAVAILABLE and the exact error below. An execution-time runner failure adds Runner failure: <detail>.

Exact error

sandbox mode "<mode>" is requested but no sandbox backend is usable on this host; refusing to run the command unconfined. Install bubblewrap or run a Landlock-enforcing kernel (Linux), ensure sandbox-exec is usable (macOS) — Windows has no confinement backend yet — or switch the consumer to danger-full-access.

Token effect

Conditional error text is visible for that call and retained in history until compaction.

KV Cache effect

Append-only; newly visible content follows the reusable request prefix and does not invalidate existing KV-cache entries.

Known Limitations and Deferred Work

File effects are the whole policy vocabulary — the seam expresses no network, process, syscall, device, or credential restrictions.
Same-world confinement only — containers, microVMs, and remote execution require replacing capability implementations rather than adding a provider here.
Denial reporting is a stderr dialect — the seam returns backend signatures instead of a typed runtime denial channel, so consumers that need classification must infer it from the child process's output.
One provider per context — composing different sandbox mechanisms simultaneously requires a provider-level ladder or separate Cordis contexts; callers choose policy per call, not backend identity.