The model-facing bash tools — bash, bash_output, bash_kill — registered over the ctx.bash executor seam (@deepseek-ai/dsh-bash). Pure schema + text shaping; every process concern lives behind the seam, so sandboxed or remote executor implementations swap in without changing what the model sees.

Requires a loaded executor implementation (e.g. @deepseek-ai/dsh-bash-local); the plugin stays pending until ctx.bash exists (inject: ['tools', 'bash', 'systemPrompt']).

The plugin also contributes the tool:bash prompt section (order 105) — the cross-call habit the per-tool descriptions cannot carry: check the [exit code: N] marker on every result and investigate failures before moving on. Under a sandboxing executor it additionally contributes the per-agent env:bash-sandbox section (order 110) stating each session's EFFECTIVE mode, and the pre-step narrator — see Per-session mode.

Tools

`bash`

Arg	Type	Notes
`command`	string (required)	Run via `bash -c`. No state persists between calls — use `workdir`, not `cd`.
`description`	string (required)	One-line, active-voice summary of the command (5-10 words), for UI/log display only — no effect on execution.
`timeoutMs`	number	Timeout override in milliseconds. The executor applies its configured default and cap.
`workdir`	string	Working directory for this call. Defaults to the calling agent's session cwd (`session.header.cwd`) so each session runs in its own workspace; a relative `workdir` is resolved against that session cwd.
`run_in_background`	boolean	Return a task id immediately; no timeout applies.
`sandbox_permissions`	string enum	ADVERTISED ONLY when the mounted executor sandboxes (`ctx.bash.sandboxMode` reports a confining default): the wider mode a denied command needs, from the closed target vocabulary `workspace-write`/`danger-full-access` (never cut down to the executor's default — the effective mode is per-session; strict widening is checked at execution against it, and a non-widening request fails without prompting anyone).
`justification`	string	Required together with `sandbox_permissions` (each without the other is a validation error): one sentence for the user explaining why this exact command needs the wider access.

command, workdir, and timeoutMs are resolved against the executor's config defaults via ctx.bash.resolve() before execution, so the executor seam (BashExecSpec) receives explicit workdir/timeoutMs values. The workdir default is applied in the tool layer (from the calling agent's session.header.cwd) BEFORE resolve() — the per-session cwd must come from exec.agent, since N sessions share one executor; only when no session cwd is available does the executor fall back to its own config / process.cwd().

Result text: stdout, then a [stderr] section, then status markers — [sandbox: file access denied under <mode> mode] when a sandboxing executor classified the failure as a policy denial (reported first so [exit code: N] stays the last line; the static description tells the model a denial is policy, not a command bug, and forbids retrying around it), [timed out after Nms] whenever the executor's timer fired (reported independently of how the process ended, so a command that traps SIGTERM and exits 0 still shows it), [killed by signal: …] for a signal death, [exit code: N] for a non-zero exit (reported, not isError: the model decides how to react), and [output truncated; full output: <path>] when the tail was kept and a safe spill file is available. If the executor knows output was dropped but cannot safely advertise a complete spill file, the path is reported as (unavailable). Only infrastructure failures (spawn errors, aborts) surface as isError results.

`bash_output`

task_id → output produced since the previous bash_output call plus a status line (running / completed, exit code: N / killed). A settled task classified as a sandbox denial carries the same [sandbox: file access denied under <mode> mode] marker on every read that sees it (denials are only classifiable once the whole stderr has been collected). Reads that lost data to buffer bounds say so and point at the full-output spill file when one is safely available, otherwise (unavailable).

`bash_kill`

task_id → ask the executor to kill the background task. The concrete executor decides how to signal or stop the process; killing an already-finished task is a reported no-op, and unknown ids are errors.

Task ownership (cross-session isolation)

The owning agent's session token (session.header.id) is stamped onto the task at spawn — passed to the executor via resolve({ …, owner }) and stored ON THE TASK inside the executor (the dsh-bash ownerOf(id) seam), not in a plugin-local map. bash_output/bash_kill compare ctx.bash.ownerOf(id) to the caller's token (session.header.id) with !== undefined semantics and reject a task owned by a different session with task <id> belongs to another session (a task started with no agent — a non-loop caller — has no owner token and is open to anyone; a call with no exec.agent cannot access an owned task). Task ids are global and predictable, so under multi-session ACP this token check is the fence that stops one session's agent from reading or killing another session's background task. Because ownership lives on the task in the executor (disposed with the dsh-bash fiber), it survives an independent tool-bash HMR reload — closing the old plugin-local-map gap where a reload orphaned pre-reload tasks. (The onTaskDone listener is still effect-scoped to this plugin's apply, so a completion landing during the reload gap still drops its one notice — the pre-existing reload-gap drop — but the ownership fence itself is HMR-proof.)

UI presentation

UI presentation is tool-owned through presentCall and presentResult. Foreground bash uses a terminal card whose title is the command, optional description is separate, and cwd follows workdir or the session; its result carries raw output and exit or signal data. Background runs, spawn failures, bash_output, and bash_kill use generic cards. Presenters are pure and replay-safe, and malformed older arguments fall back to generic rendering. See dsh-tools and dsh-acp for card semantics.

Background completion notices

When a background task finishes, a short notice is injected into the owning agent's session (agent.inject(), source {kind: 'plugin', plugin: 'tool-bash'}). The owning agent is found by its session token: the listener reads ctx.bash.ownerOf(task.id) and scans ctx.get('agents')?.list() for an agent whose session.header.id matches (read via ctx.get — onTaskDone runs on the bash fiber, a foreign fiber, so the ctx.agents proxy would throw). If no live agent carries that token — e.g. the owning session disconnected and its agent was disposed while the task ran on — the notice is dropped cleanly. Injection is durable context for the next model request, not a wake-up — an idle agent stays idle until something sends a message. That's why the tool descriptions tell the model to poll with bash_output.

The tool builds its request from named args only

The BashExecRequest seam carries optional stdin and env, used by the hooks bridges to feed a hook command its JSON payload and CLAUDE_* env. This tool does not expose them as parameters: its request is built from command/workdir/timeoutMs/signal/owner only, so a model that includes env or stdin keys in its tool arguments has them ignored. This is not a trust boundary — a model already has equivalent power through shell syntax (FOO=bar cmd, a heredoc), and the real defense against leaking the harness's ambient secrets is dsh-bash-local's credential scrub, which works regardless. A regression guard drives the real tool with those extra args and asserts the resulting request carries neither field — its job is to catch a future refactor that blindly spreads ...args into the request (which would silently forward model input into the post-scrub env merge), not to defend a wall. See the bash-stdin-env RFC.

Permissions and escalation

Commands run with the executor's full authority unless a sandboxing executor (dsh-bash-sandbox) confines them — the deny-only sandbox reports denials as result facts, rendered here as the denial marker; per-call allow/deny/ask policy is the tools/pre-execute waterfall (see docs/architecture.md).

Escalating bash calls resolve ctx.approval before execution. allowed-once applies the requested mode only to that call; rejection, cancellation, unavailability, or missing approval context executes nothing and returns a distinct error. On a real denial, the model may retry the same command once in the same turn with the narrowest sufficient mode and justification; the approval prompt itself is the consent step. Escalation is never speculative, and a disabled or rejected approval is final. The sandbox RFC owns the rationale.

Per-session mode switching

Under a sandboxing executor this plugin makes the session's standing mode override (the sandbox RFC § Per-session mode switching; the bash/sandbox-mode fold owned by dsh-bash) real at EXECUTION: every call is stamped escalation grant > session override > undefined onto BashExecRequest.sandboxMode; without either, the executor's resolve() applies its configured default. Nothing is stamped under a non-sandboxing executor (nothing would honor it) or for an agent-less caller (no session to fold). The prompt deliberately does NOT state the mode and a switch is not narrated: a standing declaration teaches the model to refuse preemptively, while the denial marker already names the mode the command ran under exactly when the boundary is hit — behavior, not belief, carries the state.