deepseek-harness/packages/sandbox/sandbox-policy

dsh-sandbox-policy — the sandbox policy home (ctx.sandboxPolicy)

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The single owner of sandbox-policy resolution: the deployment's default SandboxMode and fallback root, plus each session's durable mode override and immutable workspace root. Every enforcing capability family receives one resolved mode-and-root policy per call.

Why a shared home

Two families enforce the same mode vocabulary: the sandboxed bash executor (@deepseek-ai/dsh-bash-sandbox) and the sandboxed filesystem provider (@deepseek-ai/dsh-fs-sandbox). If each resolved its own mode + workspaceRoot, the two could drift into a split world — bash confined to one root while fs fences another, exactly what the sandbox RFC warns against. Both tool layers resolve policy through ctx.sandboxPolicy, and both enforcing backends consume that complete per-call result. The cross-family fs sandbox RFC records the shared-policy decision.

Config

• mode — the deployment default SandboxMode (read-only / workspace-write / danger-full-access), validated at load. Default read-only (fail-safe).
• workspaceRoot — the fallback directory workspace-write may write under for agentless calls or sessions without a cwd. Default process.cwd(), resolved to its absolute filesystem identity either way. A normal agent call uses its session header's immutable cwd instead.

Surface

• ctx.sandboxPolicy.resolve({ session?, mode? }) — resolves one complete per-call policy. An explicit approved mode outranks the session's override chain (overrideOf, below), which outranks defaultMode; the session's immutable cwd is canonicalized with filesystem semantics before becoming workspaceRoot, otherwise the configured fallback applies. Canonicalization precedes lexical normalization so symlink/.. agrees with process working-directory resolution.
• ctx.sandboxPolicy.defaultMode / ctx.sandboxPolicy.workspaceRoot — the deployment default and fallback root used by resolve().
• effectiveSandboxMode(events) — the pure fold of a slice of sandbox/mode events (the last switch wins, or undefined), the building block sandboxOverrideOf composes with the seed boundary and the header baseline.
• setSandboxMode(session, mode) — THE write path for a per-session override: appends exactly one sandbox/mode event. The switch IS its event; nothing mutates the mode out of band.
• ctx.sandboxPolicy.overrideOf(session) (the pure sandboxOverrideOf export, also consumed by the permission presets) — the session's override chain, never the deployment default: with an inherited sandboxMode header baseline (a delegation child), the fold of the session's OWN switches past SessionHeader.seedLength, else the baseline, validated against the closed vocabulary on read (throws on foreign values — a durable boundary); without one (a top-level session or a generic SessionStore.fork child), the whole-log fold, so seed-carried switches remain the replayed inherited truth. The in-process subagent driver captures this at delegation and writes it into each child's creation-time header, so a delegating parent's tightened mode binds its children with no first-turn timing window (rationale).
• SANDBOX_MODES — every mode, for option advertisement and runtime validation.

The optional ./invariant companion rejects a forged durable sandbox/mode event whose value falls outside that closed vocabulary; Session and its companion own the surrounding storage and turn-enclosure rules.

The per-session store

A runtime switch is one log-only sandbox/mode event on the session it applies to. effective = explicit grant ?? override chain ?? deployment default, where the override chain is sandboxOverrideOf's fold of the session's OWN post-seed switches, else the inherited header baseline — so an override survives restart by replay, a delegation child starts under its parent's captured policy, and two sessions never see each other's state. Workspace identity does not need another event: the immutable SessionHeader.cwd recorded at creation is the root for every call in that session. The event is log-only (the approval/* precedent): the model learns the mode from the enforcing tools' denial markers, never from the event.

Model Experience

Indirectly, through dsh-tool-bash and dsh-tool-fs, which render the effective mode this service holds in their [sandbox: …] denial markers and escalation prompts; the sandbox/mode event itself never reaches the model.

KV Cache effect

No direct invalidation; the named consumers own any request-prefix changes, and the mode is deliberately absent from the prompt.

Known Limitations and Deferred Work

• One primary workspace root per session — policy resolves SessionHeader.cwd; extra writable roots are not part of SandboxExecutionPolicy.
• File-effect modes only — SandboxMode governs file effects; network and process policy are outside its vocabulary, so no knob here restricts them.