# Bash Executor

English | [中文](bash.zh.md)

The bash execution seam is split across interface ([dsh-bash](../../packages/bash/bash), `ctx.bash`), implementations ([dsh-bash-local](../../packages/bash/bash-local) and [dsh-bash-sandbox](../../packages/bash/bash-sandbox)), and consumer ([dsh-tool-bash](../../packages/bash/tool-bash), the `bash` schema). Generic background-task ids, ownership, and controls live in [tasks.md](tasks.md); this seam returns a task-free process handle. Raw process-group mechanics live behind the [subprocess seam](subprocess.md).

Source: [`packages/bash/bash/src/types.ts`](../../packages/bash/bash/src/types.ts)

## Managed shell environment namespace

`DSH_*` variables are Harness-owned child-process facts. The model-facing bash tool collects them through `ctx.bashEnv` and passes them through `BashExecRequest.dshEnv`; the subprocess service removes inherited `DSH_*` names before merging the current snapshot. The `DshEnvironmentKey`/`DshEnvironment` vocabulary is owned by the [subprocess seam](subprocess.md) and re-exported by `dsh-bash`.

## Request vs. spec: the `resolve()` split

The seam separates the **model-/plugin-facing request** (optional `workdir`/`timeoutMs`/`stdoutMaxBytes`, filled from config or request policy) from the **fully-resolved spec** the executor acts on (those fields required). The tool layer calls `ctx.bash.resolve(request)` between them — this is the repo's "explicit > implicit at package seams" rule made concrete: the reader of a `BashExecSpec` never wonders where the working directory or output budget came from.

```ts type-equiv
/**
 * A caller's execution REQUEST: `workdir` and `timeoutMs` are optional and
 * filled by {@link BashExecutor.resolve} from the implementation's config.
 * This is the model-/plugin-facing shape; pass it to `resolve()` to obtain a
 * fully-resolved {@link BashExecSpec}.
 */
interface BashExecRequest {
  command: string
  /** Working directory override (default: implementation-configured). */
  workdir?: string | undefined
  /** Timeout override in milliseconds (implementations cap it). */
  timeoutMs?: number | undefined
  /**
   * Foreground stdout capture budget in bytes. Absent uses the executor's
   * default output cap. Trusted in-process consumers use this when they must
   * parse complete stdout up to their own bounded limit; the model-facing bash
   * tool does not expose it as a parameter.
   */
  stdoutMaxBytes?: number | undefined
  /** Abort signal — implementations kill the command when it fires. */
  signal?: AbortSignal | undefined
  /**
   * Bytes to write to the command's stdin, then close it. Absent leaves stdin
   * closed/empty (the default for model-driven tool calls). Set by in-process
   * plugins (e.g. the hooks bridges, which write a hook command's JSON payload
   * to its stdin); the model-facing bash tool does not expose it as a parameter
   * (a model that needs stdin uses shell syntax like a heredoc or a pipe).
   */
  stdin?: string | undefined
  /**
   * Ordinary environment entries for the command, merged after the credential
   * scrub. `DSH_*` is reserved for {@link dshEnv} and implementations reject it
   * here. Set by in-process plugins (the hooks bridges set
   * `CLAUDE_PROJECT_DIR`, `CLAUDE_PLUGIN_ROOT`, …); the model-facing bash tool
   * does not expose it as a parameter.
   */
  env?: Record<string, string> | undefined
  /**
   * Harness-owned `DSH_*` variables for this execution. Executors discard
   * ambient `DSH_*` entries before merging this snapshot, so an unavailable
   * current fact cannot inherit a stale value from the harness process, and
   * reject non-`DSH_*` names supplied through this managed channel.
   */
  dshEnv?: DshEnvironment | undefined
  /** Fully resolved per-call sandbox policy; sandboxing executors default it. */
  sandboxPolicy?: SandboxExecutionPolicy | undefined
}
```

```ts type-equiv
/**
 * A resolved execution spec. {@link BashExecutor.resolve} fills and caps the
 * required fields; {@link BashExecutor.start} ignores `timeoutMs` because
 * background processes have no executor timeout.
 */
interface BashExecSpec {
  command: string
  workdir: string
  timeoutMs: number
  /**
   * Resolved foreground stdout capture budget in bytes. `run()` uses it for
   * stdout; background tasks and stderr keep the executor's own output cap.
   */
  stdoutMaxBytes: number
  /** Abort signal — implementations kill the command when it fires. */
  signal?: AbortSignal | undefined
  /** Bytes to write to stdin before closing it; absent means no stdin. */
  stdin?: string | undefined
  /**
   * Ordinary environment entries carried through from
   * {@link BashExecRequest.env}. `DSH_*` remains reserved for {@link dshEnv}.
   * OPTIONAL on the spec for the same reason as `stdin`: absent means no
   * ordinary extra environment.
   */
  env?: Record<string, string> | undefined
  /** Managed `DSH_*` snapshot; implementations reject ordinary names. */
  dshEnv?: DshEnvironment | undefined
  /** Resolved sandbox policy; ignored by executors that do not confine. */
  sandboxPolicy: SandboxExecutionPolicy | undefined
}
```

`stdin` and `env` are trusted in-process plugin inputs and are not exposed by `dsh-tool-bash`. The local executor scrubs ambient credentials before merging explicit caller-supplied env. See [the bash-stdin-env Agent Note](../../.agents/notes/implemented/architecture/2026-06-30-bash-stdin-env-trusted-plugin-surface.md).

`stdoutMaxBytes` is also trusted-plugin-only. It lets a foreground consumer request complete stdout up to a bounded parser budget without changing stderr, background tasks, or the model-facing bash tool's ordinary output cap.

## Foreground runs: `BashRunResult`

The outcome of one completed (or killed) foreground run. Orthogonal outcomes are reported **independently** — a process can both time out AND exit 0 because it trapped the signal — so `timedOut`, `aborted`, `signal`, and `exitCode` are each their own field; a caller never reads a cut-short run as a clean success.

```ts type-equiv
/** The outcome of one completed (or killed) foreground run. */
interface BashRunResult {
  /** Exit code; null when the process died from a signal. */
  exitCode: number | null
  /** Terminating signal (e.g. 'SIGTERM'); null on normal exit. */
  signal: NodeJS.Signals | null
  /**
   * True when the executor's own timeout was the FIRST cause to cut the command
   * short. Mutually exclusive with {@link aborted}: one fused deadline drives
   * both the timeout and the caller's cancellation, so a timeout and an abort
   * racing before process close report the single first-abort cause, not both
   * (see the [timeout-library Agent Note](../../../../.agents/notes/implemented/architecture/2026-07-06-timeout-deadline-library.md)).
   */
  timedOut: boolean
  /**
   * True when the caller's `AbortSignal` was the FIRST cause to kill the command
   * (and it was not the executor's own timeout). Mutually exclusive with
   * {@link timedOut} — see there for the first-cause classification.
   */
  aborted: boolean
  /** The effective timeout applied to this run (after defaulting/capping). */
  timeoutMs: number
  stdout: CollectedOutput
  stderr: CollectedOutput
  /** Sandbox execution facts, absent for an unsandboxed executor. */
  sandbox?: BashSandboxInfo
}
```

Each stream is a `CollectedOutput` — the (possibly truncated) text plus recovery info; when truncated, `text` is the **tail** and the complete stream spills to a private file. The shape is owned by the [subprocess seam](subprocess.md) and re-exported by `dsh-bash`.

## File sandbox: `BashSandboxInfo`

A sandbox-consuming executor exposes its configured mode fallback through `BashExecutor.sandboxMode`. The tool layer asks [`@deepseek-ai/dsh-sandbox-policy`](../../packages/sandbox/sandbox-policy/README.md) to resolve each calling session's durable `sandbox/mode` override and immutable cwd into `BashExecRequest.sandboxPolicy`; a user-approved strictly wider call replaces only the mode. The mode/root/enforcement vocabulary is owned by the [`@deepseek-ai/dsh-sandbox` seam](sandbox.md); modes govern file effects only.

A sandboxed run reports its mode, conservative denial classification, and enforcement completeness. `runnerFailed` marks a sandbox runner failure before the command ran; foreground execution throws `SANDBOX_UNAVAILABLE`, while a settled background process has only its facts channel.

```ts type-equiv
/**
 * Sandbox facts for one run, present iff a sandboxing executor handled it.
 * Facts are reported independently of process exit status so callers can
 * distinguish command failures from policy denials and runner failures.
 */
interface BashSandboxInfo {
  /** The mode the command actually ran under. */
  mode: SandboxMode
  /** Whether the sandbox denied a file operation. */
  denied: boolean
  /** How completely the selected runner enforced the requested mode. */
  enforcement?: SandboxEnforcement
  /** Whether the sandbox runner failed before the command could run. */
  runnerFailed?: boolean
}
```

One more piece completes the vocabulary: the `SANDBOX_UNAVAILABLE` error code (owned by the [sandbox seam](sandbox.md)) is what the `ctx.sandbox` provider throws — and the executor propagates — when a confined mode has no usable backend. A selected runner refusing its profile reaches the same fail-closed foreground error; a settled background task records `runnerFailed`. The model receives denial/runner facts in results, learns the effective mode only when a denial marker names it, and can request a one-shot strictly wider retry through `sandbox_permissions` plus `justification`; `ctx.approval` must grant that exact call before anything executes. The complete policy and switching design is the [sandbox Agent Note](../../.agents/notes/implemented/feature/2026-07-06-sandbox.md).

## Background processes: `BashProcess`

`start()` returns a handle with no id or owner. `dsh-tool-bash` adapts it into `ctx.tasks.start()` hooks; the generic runtime then owns task identity and lifecycle. `done` resolves when the process closes and never rejects, reads remain valid after settlement, and sandbox facts are stamped before `done` resolves.

```ts type-equiv
/**
 * A background process handle returned by {@link BashExecutor.start}. It is the
 * only access path; buffered output remains readable after exit. Composition
 * teardown (the subprocess service's disposal) kills running processes and
 * awaits {@link done}; an executor-only reload leaves them running.
 */
interface BashProcess {
  /** Process lifecycle state (settled exactly once). */
  status: BashProcessStatus
  /** Exit code once finished (null = killed by signal / still running). */
  exitCode: number | null
  /** Terminating signal name, when signal-killed. */
  signal: NodeJS.Signals | null
  /** Resolves when the underlying process closes (never rejects — a spawn failure settles as `killed` with the error on stderr). */
  readonly done: Promise<void>
  /** Sandbox facts, stamped once a confined process settles. */
  sandbox?: BashSandboxInfo
  /**
   * Read output produced since the previous read (consuming — consecutive
   * reads never re-deliver). Reads that lost data flag `lossy` and point at
   * full-stream spill files when available.
   */
  readOutput(): BashProcessRead
  /**
   * Kill the process group. Returns false when it had already finished
   * (no-op); idempotent.
   */
  kill(): boolean
}
```

`readOutput()` returns the incremental delta and spill recovery facts:

```ts type-equiv
/** One incremental {@link BashProcess.readOutput} read. */
interface BashProcessRead {
  /** Output produced since the previous read (stderr in a marked section). */
  delta: string
  /** True when truncation dropped unread bytes the delta cannot include. */
  lossy: boolean
  /** Full stdout spill file, when stdout truncation occurred and a safe path is available. */
  stdoutSpillPath?: string
  /** Full stderr spill file, when stderr truncation occurred and a safe path is available. */
  stderrSpillPath?: string
}
```

## The service

`BashExecutor` owns `resolve`, foreground `run`, background-process `start`, and the `sandboxMode` capability fact. `dsh-bash-local` owns command defaulting, timeout/abort classification, the terminal environment, and the background read merge; process groups, bounded collectors, spill files, credential scrubbing, and disposal quiescence are the [subprocess service](subprocess.md)'s. `dsh-tool-bash` owns model-facing rendering and adapts background handles into the [generic task runtime](tasks.md).
