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@@ -22,9 +22,10 @@ Three coordinated pieces, all composed from the leaf `cordis.yml`, none touching
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- `Config`: `mode` (the closed `SandboxMode` union, default `read-only`) and `workspaceRoot` (default the process cwd, resolved absolute). Misconfiguration fails loud at load.
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- The per-session override event `sandbox/mode`, with its pure fold (`effectiveSandboxMode(events)`), its write path (`setSandboxMode(session, mode)`), and `SANDBOX_MODES`. The event is policy state — consumed by two families — so it lives here, not in either capability's seam. Its shape and log-only semantics match the `approval/*` precedent.
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-- `defaultMode` / `workspaceRoot` accessors the enforcing implementations read for their resolve fallback and boundary.
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+- `resolve({ session?, mode? })`, which returns a complete per-call `SandboxExecutionPolicy`: explicit approved mode > the session fold > `defaultMode`, and the session's immutable cwd > configured `workspaceRoot` fallback.
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+- `defaultMode` / `workspaceRoot` accessors retained as deployment fallbacks and the capability-advertisement fact.
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-`dsh-bash-sandbox` carries no sandbox config of its own — it injects `sandboxPolicy` and reads the default from it; its `resolve()` precedence is unchanged (escalation grant > per-call stamp > default). `dsh-tool-bash` and `dsh-tool-fs` fold the session's `sandbox/mode` with `effectiveSandboxMode` to stamp each call; `dsh-permission` presets and the ACP bridge write through the relocated setter. The seam that owns bash execution no longer depends on `dsh-session` at all — the session dependency moved to the policy package with the fold.
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+`dsh-bash-sandbox` carries no sandbox config of its own — it injects `sandboxPolicy` and uses its deployment fallback only for direct calls. `dsh-tool-bash` and `dsh-tool-fs` pass the active session to `ctx.sandboxPolicy.resolve()`, so both receive the same effective mode and cwd root on every call; `dsh-permission` presets and the ACP bridge write through the relocated setter. The seams that own bash and fs execution remain session-free — the session dependency lives in the policy package and tool consumers.
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### `dsh-fs-sandbox` — enforcement inside the provider
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@@ -34,13 +35,13 @@ Three coordinated pieces, all composed from the leaf `cordis.yml`, none touching
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- `workspace-write` fences the canonicalized target against the writable-root set — `writableRoots(policy)` in `dsh-sandbox`: the workspace root plus the platform temp areas (`/tmp`, `os.tmpdir()`), each realpathed — the SAME set the Seatbelt profile grants, so the fs fence is the fourth dialect of one mode meaning alongside the bwrap/Landlock/Seatbelt profiles, and "the write tool cannot write `/tmp` but bash can" asymmetries cannot arise. Canonical spellings take a lexical containment fast path; when Windows exposes one directory through different casing or long-name/8.3 spellings, an ancestor walk compares filesystem identity rather than weakening the boundary to textual prefix guesses. The target is re-canonicalized (`resolve` realpaths the deepest existing ancestor) immediately before delegating, so an ancestor symlink swapped since the tool resolved it is caught.
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- `danger-full-access` delegates unfenced.
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-A denial is the structured `FS_SANDBOX_DENIED` carrying the effective mode — distinct from `FS_PERMISSION_DENIED` (a host EACCES is the world refusing; this is policy refusing). No text inference: an in-process fence knows exactly what it denied. The per-call carrier is a trailing optional `sandboxMode` on `writeText`/`editText` (the filesystem twin of `BashExecRequest.sandboxMode`); the seam stays session-free (the caller stamps, exactly as `resolve` takes a cwd), and the bare local backend carries-and-ignores it. `FileSystem.sandboxMode` is the capability fact (`undefined` on the base and `fs-local`, the default on `SandboxedFileSystem`), so the tool layer advertises escalation from composition truth.
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+A denial is the structured `FS_SANDBOX_DENIED` carrying the effective mode — distinct from `FS_PERMISSION_DENIED` (a host EACCES is the world refusing; this is policy refusing). No text inference: an in-process fence knows exactly what it denied. The per-call carrier is a trailing optional `SandboxExecutionPolicy` on `writeText`/`editText` (the filesystem twin of `BashExecRequest.sandboxPolicy`); the seam stays session-free, and the bare local backend ignores it. `FileSystem.sandboxMode` is the capability fact (`undefined` on the base and `fs-local`, the default on `SandboxedFileSystem`), so the tool layer advertises escalation from composition truth.
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The threat model is stated in the package README: a policy fence in trusted code over model-controlled paths, not a kernel boundary — the operations are the seam's own, only the target path is untrusted, so canonicalize-then-contain is the complete answer to this surface (the `code-runtime` "containment, not a security boundary" precedent). Kernel-grade isolation of untrusted CODE stays `ctx.bash`'s job. The residual resolve-to-syscall race is narrowed by the in-place re-canonicalization and eliminated only by platform primitives (`openat2` `RESOLVE_BENEATH`) not worth their portability cost here.
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### Tool parity — one denial marker, one escalation flow
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-`dsh-tool-fs` stamps the effective mode onto each mutation and maps `FS_SANDBOX_DENIED` to the marker the model already knows from bash: `[sandbox: file access denied under <mode> mode]`. When `ctx.fs.sandboxMode` reports a confining mode at registration, `write` and `edit` advertise the same `sandbox_permissions` + `justification` fields, teach the same same-turn retry, and resolve the same `ctx.approval` request before executing — the four outcomes and their verbatim fail-closed texts carried over from [the sandbox Agent Note](2026-07-06-sandbox.md) § Escalation (strict widening checked at execution against the call's effective mode; a grant consumed by the one call that asked; no new session events).
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+`dsh-tool-fs` resolves the active session's complete policy onto each mutation and maps `FS_SANDBOX_DENIED` to the marker the model already knows from bash: `[sandbox: file access denied under <mode> mode]`. When `ctx.fs.sandboxMode` reports a confining mode at registration, `write` and `edit` advertise the same `sandbox_permissions` + `justification` fields, teach the same same-turn retry, and resolve the same `ctx.approval` request before executing — the four outcomes and their verbatim fail-closed texts carried over from [the sandbox Agent Note](2026-07-06-sandbox.md) § Escalation (strict widening checked at execution against the call's effective mode; a grant changes only that call's mode and retains its session root; no new session events).
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The shared pieces live in `dsh-sandbox`, which owns the mode types: `WIDER_MODES`, the escalation-target enum, the argument-pairing validation, the denial/hint marker builders, and `approveEscalation` — the ordered fail-closed choreography. `approveEscalation` takes a minimal STRUCTURAL approver (`EscalationApprover`, generic over the agent and call-id types), not the approval service type, so `dsh-sandbox` gains no dependency on the approval or agent packages: each tool passes its own `ctx.approval`, agent, call id, and tool name as ingredients. `dsh-tool-bash` and `dsh-tool-fs` both use these; the cross-file duplication gate holds the single-sourcing honest.
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@@ -53,7 +54,8 @@ The sandbox Agent Note's original cross-family sketch put fs enforcement on the
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### Out of scope
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- **Network policy for `ctx.web`** — `SandboxMode` claims file effects only; a web-only network knob while bash `curl` runs free would be a false boundary. Revisit when a bash backend enforces network (bwrap `--unshare-net`, Landlock ABI v4+).
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-- **The `subagent-acp` consumer** and **per-session workspace root** — unchanged deferred phases of the sandbox RFC; centralizing the root in `ctx.sandboxPolicy` is groundwork for the latter, not its design.
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+- **The `subagent-acp` consumer** — unchanged deferred phase of the sandbox RFC.
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+- **Additional writable roots inside one session** — the resolved policy carries one primary `SessionHeader.cwd`; ACP `additionalDirectories` remains a separate bridge and policy design.
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- **A uniform per-tool sandbox runtime** — remains rejected for the reasons in the sandbox RFC.
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## Alternatives considered
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@@ -66,7 +68,7 @@ The sandbox Agent Note's original cross-family sketch put fs enforcement on the
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- **Per-family policy config with a load-time consistency check** — rejected: two homes for one fact, patched by a check that must enumerate every future enforcing family; the policy service makes drift inexpressible instead of detected.
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- **Keep the override event in `dsh-bash` as `bash/sandbox-mode`** — rejected: the event is policy state consumed by two families; leaving it bash-named forces `dsh-fs-sandbox` to depend on bash vocabulary. Pre-release, the rename is a same-change move with snapshot re-records, no shims.
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- **Escalation choreography imported from the approval/agent packages into `dsh-sandbox`** — rejected: it would invert the layering (a base vocabulary package depending on UI/agent packages). The structural approver keeps the logic single-sourced in `dsh-sandbox` while the dependencies stay in the tool layer that already holds them.
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-- **A consolidated mutation-options object on the fs seam** (the shape first sketched for the per-call carrier) — rejected on friction: it churns every `writeText`/`editText` caller and splits `signal` across an options bag for mutations while reads keep it positional. A trailing optional `sandboxMode` matches bash's carry-and-ignore pattern and keeps `signal` symmetric across the seam.
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+- **A consolidated mutation-options object on the fs seam** (the shape first sketched for the per-call carrier) — rejected on friction: it splits `signal` across an options bag for mutations while reads keep it positional. A trailing optional `SandboxExecutionPolicy` matches bash's carry-and-ignore pattern and keeps `signal` symmetric across the seam.
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- **Extra writable-root grants on `SandboxPolicy` now** — deferred unchanged: `writableRoots()` derives from the mode meaning today; ad-hoc grants are an escalation-scope question the sandbox RFC left open.
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## Consequences
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@@ -77,6 +79,7 @@ What shipped — the tiers in § Testing hold each:
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- Under `workspace-write`, mutations land under the workspace root and the temp areas and are denied outside; the containment matrix — `..` traversal, absolute paths outside, a pre-existing symlinked directory inside pointing out, a new file created under such a symlink, and alias-equivalent root spellings — denies every escape while admitting the same directory identity on real disks.
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- A denied fs mutation retried once with `sandbox_permissions` + `justification` prompts through the composed approval chain; a grant runs exactly that call under the wider mode and the write lands; rejected/cancelled/unavailable each produce their verbatim fail-closed text and mutate nothing.
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- One `permission` preset switch governs both families: after a session switches modes, the next bash call and the next fs mutation both honor the new mode from the same `sandbox/mode` fold.
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+- Concurrent sessions with different cwd roots carry different policies through the same service instances; neither family caches one session's root for the next call.
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- A direct `ctx.fs.writeText` with no per-call stamp is confined at the deployment default.
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- The escalation fields on `write`/`edit` exist exactly when the mounted `ctx.fs` confines, absent under `dsh-fs-local`.
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- `agent-loop` is untouched — everything rides `ctx.sandboxPolicy`, the `ctx.fs` seam, `SessionEventMap` merging, and the tool-execution pipeline.
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@@ -90,5 +93,6 @@ Costs and accepted limits:
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## Testing
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-- Unit: `dsh-sandbox` pins the escalation ladder, the marker builders, the argument-pairing validation, and `approveEscalation`'s ordered fail-closed sequence (non-widening, no-approval, no-agent, each outcome), plus `writableRoots`/`canonicalPath`. `dsh-sandbox-policy` pins the default accessors, the fold/setter, the load-time mode rejection, and HMR safety. `dsh-fs-sandbox` pins the per-mode fence and the containment matrix (inside, temp area, absolute-outside, `..`, symlinked-out directory, new file under one, path-equals-root, filesystem-root, and alias-equivalent spelling) on a real filesystem, plus the per-call override and HMR safety. `dsh-tool-fs` pins advertisement gating, the mode stamp, the fold, denial-marker mapping, and the full escalation matrix (grant, reject, no-service, no-agent, pairing, non-confining guard). `dsh-tool-bash`, `dsh-bash-sandbox`, and `dsh-permission` migrate to the relocated policy/kit.
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+- Unit: `dsh-sandbox` pins the escalation ladder, the marker builders, the argument-pairing validation, and `approveEscalation`'s ordered fail-closed sequence (non-widening, no-approval, no-agent, each outcome), plus `writableRoots`/`canonicalPath`. `dsh-sandbox-policy` pins deployment fallback, session mode/root resolution, explicit-mode precedence, the fold/setter, load-time mode rejection, and HMR safety. `dsh-fs-sandbox` pins the per-policy fence and containment matrix (inside, temp area, absolute-outside, `..`, symlinked-out directory, new file under one, path-equals-root, filesystem-root, root-ending-in-separator, and alias-equivalent spelling) on a real filesystem, plus per-call override and HMR safety. `dsh-tool-fs` pins advertisement gating, complete policy resolution, denial-marker mapping, and the full escalation matrix (grant, reject, no-service, no-agent, pairing, non-confining guard). `dsh-tool-bash`, `dsh-bash-sandbox`, and `dsh-permission` consume the same policy kit.
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+- Keyless e2e: one real Cordis context creates two agents with different session cwd roots, runs the shipped bash and fs tools concurrently, and world-verifies that own-project writes land while both cross-project writes are denied.
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- Snapshot: the acp-agent example composes `dsh-sandbox-policy` + `dsh-fs-sandbox`; the pinned header carries the fs escalation fields and the `sandbox/mode` event name, re-recorded once.
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