Tianyi Cui
bb9ae2ba99
Address review: the "trusted-plugin surface" framing overstated the security story. A model driving the `bash` tool already has equivalent power to set env vars and feed stdin through ordinary shell syntax (`FOO=bar cmd`, heredocs), so the `env`/`stdin` seam fields grant it no new capability — and they cannot exfiltrate the harness's ambient credentials, because the credential SCRUB in dsh-bash-local (which strips *KEY*/*SECRET*/*TOKEN* from process.env before the child sees it) is the actual control, and it works regardless of these fields (tool-call args are static JSON, never shell-evaluated). So drop the "dangerous / trusted-plugin boundary" language across the RFC, the three bash-package READMEs, the bash/src/types.ts JSDoc, and docs/bash.md (both the type-equiv blocks — kept 1:1 with source — and the prose). The reality that remains: the `bash` tool doesn't EXPOSE env/stdin as parameters because they'd be redundant with shell syntax; the fields exist for in-process plugins (the hooks bridges) to pass a JSON payload + CLAUDE_* vars cleanly. The guard test is kept but reframed: it catches a future `...args` spread that would silently forward model input into the post-scrub env merge, NOT a trust wall. No code or behavior change.
162 lines
10 KiB
Markdown
162 lines
10 KiB
Markdown
# Bash Executor
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The bash execution seam — the canonical [capability seam](../rfc/implemented/architecture/2026-06-13-capability-seams.md) example, split across three packages: interface ([dsh-bash](../../packages/bash/bash), `ctx.bash`), implementation ([dsh-bash-local](../../packages/bash/bash-local), local subprocesses), and consumer ([dsh-tool-bash](../../packages/bash/tool-bash), the `bash`/`bash_output`/`bash_kill` tool schemas). Bash is **one optional capability**, not part of the agent-loop spine — so its vocabulary lives here, not in [core.md](core.md). A sandboxed, containerized, or remote backend is a sibling package implementing the same interface.
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Source: [`packages/bash/bash/src/types.ts`](../../packages/bash/bash/src/types.ts)
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## Request vs. spec: the `resolve()` split
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The seam separates the **model-/plugin-facing request** (optional `workdir`/`timeoutMs`, filled from config) 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 came from.
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```ts type-equiv
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interface BashExecRequest {
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command: string
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/** Working directory override (default: implementation-configured). */
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workdir?: string | undefined
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/** Timeout override in milliseconds (implementations cap it). */
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timeoutMs?: number | undefined
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/** Abort signal — implementations kill the command when it fires. */
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signal?: AbortSignal | undefined
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/**
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* Bytes to write to the command's stdin, then close it. Absent leaves stdin
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* closed/empty (the default for model-driven tool calls). Set by in-process
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* plugins (e.g. the hooks bridges, which write a hook command's JSON payload
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* to its stdin); the model-facing bash tool does not expose it as a parameter
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* (a model that needs stdin uses shell syntax like a heredoc or a pipe).
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*/
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stdin?: string | undefined
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/**
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* Extra environment entries for the command, merged AFTER the
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* implementation's credential scrub (so an explicit entry here is honored even
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* when its name matches the scrub pattern — the caller named a value it holds,
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* not the harness's ambient secret). Set by in-process plugins (the hooks
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* bridges set `CLAUDE_PROJECT_DIR`, `CLAUDE_PLUGIN_ROOT`, …); the model-facing
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* bash tool does not expose it as a parameter (a model that needs an env var
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* uses shell syntax like `FOO=bar cmd`).
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*/
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env?: Record<string, string> | undefined
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/**
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* Opaque OWNER token for a background task — the consumer's isolation key
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* (the tool layer passes the owning agent's `session.header.id`). The
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* executor stores it on the task and exposes it via {@link BashExecutor.ownerOf};
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* the executor itself NEVER interprets it (no access policy lives in the
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* seam — that is the consumer's job). Absent for foreground runs and for an
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* ownerless background start (a non-agent caller).
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*/
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owner?: OwnerToken | undefined
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}
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```
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```ts type-equiv
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interface BashExecSpec {
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command: string
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workdir: string
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timeoutMs: number
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/** Abort signal — implementations kill the command when it fires. */
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signal?: AbortSignal | undefined
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/**
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* Bytes to write to the command's stdin (then close it), carried through
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* verbatim from {@link BashExecRequest.stdin}. OPTIONAL on the resolved spec
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* (unlike `owner`): it has no config default, so a missing one means "no
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* stdin" — the safe, ordinary case — not a silent footgun, so it stays a
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* plain optional rather than required-but-nullable (see the request field).
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*/
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stdin?: string | undefined
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/**
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* Extra environment entries, carried through verbatim from
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* {@link BashExecRequest.env} and merged by the implementation AFTER its
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* credential scrub (an explicit entry wins even when its name matches the
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* scrub pattern). OPTIONAL on the spec for the same reason as `stdin` — no
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* config default, absent means "no extra env".
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*/
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env?: Record<string, string> | undefined
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/**
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* Opaque owner token, REQUIRED-but-nullable (mirrors `workdir`/`timeoutMs`
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* being required on the resolved spec): {@link BashExecutor.resolve} carries
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* the request's `owner` through, defaulting a missing one to `undefined`. A
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* required field makes a forgotten owner a VISIBLE `undefined` rather than a
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* silently-absent property that yields an unowned (cross-session-readable)
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* task. `start()` stores it; `run()` (foreground) ignores it.
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*/
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owner: OwnerToken | undefined
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}
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```
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The `owner` token is the isolation key: the executor stores it but never interprets it (access policy is the consumer's job), so a background task started by one agent isn't readable cross-session. A required-but-nullable field makes a forgotten owner a visible `undefined` rather than a silently-unowned task.
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`stdin` and `env` are set by in-process plugins (the hooks bridges, native plugins) to feed a hook command its JSON payload on stdin and its `CLAUDE_PROJECT_DIR`/`CLAUDE_PLUGIN_ROOT` env. The model-facing `dsh-tool-bash` tool does not expose them as parameters — its request is built from `command`/`workdir`/`timeoutMs`/`signal`/`owner` only — because a model already has equivalent power through shell syntax (`FOO=bar cmd`, a heredoc), so duplicating them as tool params would be redundant. This is NOT a security boundary: the credential scrub in `dsh-bash-local` is what stops the harness's ambient secrets reaching a spawned command, and it works regardless of these fields (a model cannot read a value the scrub removed, and tool-call args are static JSON, never shell-evaluated). A guard test asserts the tool doesn't forward model `env`/`stdin` — to catch a future `...args` spread, not to defend a trust wall. `env` is merged AFTER the scrub so an explicit caller entry (a value it already holds) wins even on a credential-shaped name. See [the bash-stdin-env RFC](../rfc/implemented/architecture/2026-06-30-bash-stdin-env-trusted-plugin-surface.md).
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Both ids the seam handles are [branded](core.md) (zero-cost `string` brands, the same machinery as `SessionId`/`AgentId`): `BashTaskId` (a tracked background task, generated `bash-N` by the local executor) and `OwnerToken` (the opaque isolation key). `OwnerToken` is deliberately a DISTINCT brand from `SessionId`, not an alias: the bash seam is a capability seam that must not know what an owner token *means*, so it never imports `dsh-session`'s vocabulary — the `dsh-tool-bash` consumer is the single boundary that casts the owning agent's `SessionId` into an `OwnerToken`. Branding both stops a raw `string` (or a `BashTaskId` where an `OwnerToken` is expected, or vice versa) from slipping through the type checker on the model-facing `task_id` path.
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## Foreground runs: `BashRunResult`
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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.
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```ts type-equiv
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interface BashRunResult {
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/** Exit code; null when the process died from a signal. */
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exitCode: number | null
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/** Terminating signal (e.g. 'SIGTERM'); null on normal exit. */
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signal: NodeJS.Signals | null
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/** True when the executor's own timeout killed the command. */
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timedOut: boolean
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/** True when the caller's AbortSignal killed the command. */
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aborted: boolean
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/** The effective timeout applied to this run (after defaulting/capping). */
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timeoutMs: number
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stdout: CollectedOutput
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stderr: CollectedOutput
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}
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```
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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:
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```ts type-equiv
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interface CollectedOutput {
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/** Collected text — the TAIL of the stream when truncated. */
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text: string
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/** True when bytes were dropped from `text`. */
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truncated: boolean
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/** Path to a file holding the COMPLETE stream, when truncated and available. */
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spillPath?: string
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}
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```
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## Background tasks: `BashTask`
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A long-running command started with `start()` is tracked as a `BashTask`. `BashTaskStatus` is `'running' | 'completed' | 'killed'`; `done` resolves when the underlying process closes and never rejects.
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```ts type-equiv
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interface BashTask {
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readonly id: BashTaskId
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readonly command: string
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status: BashTaskStatus
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/** Exit code once finished (null = killed by signal / still running). */
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exitCode: number | null
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/** Terminating signal name, when signal-killed. */
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signal: NodeJS.Signals | null
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/** Resolves when the underlying process closes (never rejects). */
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readonly done: Promise<void>
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}
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```
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`readOutput()` returns an incremental `BashTaskRead` — the output produced since the previous read, with a `lossy` flag when truncation dropped unread bytes:
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```ts type-equiv
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interface BashTaskRead {
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task: BashTask
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/** Output produced since the previous read (stderr in a marked section). */
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delta: string
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/** True when truncation dropped unread bytes the delta cannot include. */
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lossy: boolean
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/** Full stdout spill file, when stdout truncation occurred and a safe path is available. */
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stdoutSpillPath?: string
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/** Full stderr spill file, when stderr truncation occurred and a safe path is available. */
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stderrSpillPath?: string
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}
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```
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## The service
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`BashExecutor` (`ctx.bash`, abstract — defined in [`packages/bash/bash/src/index.ts`](../../packages/bash/bash/src/index.ts)) mirrors the `LlmService`/`LlmAdapter` split: `resolve` (request → spec), `run` (foreground), `start` (background), `get`/`ownerOf`/`list`/`readOutput`/`kill`, and `onTaskDone` (a `BashTaskListener` completion callback). Spawned commands get a **scrubbed env** (dropping `*KEY*`/`*SECRET*`/`*TOKEN*`) and spill files use a private 0700 dir with random names and owner-only opens — model output never gets the ambient environment or a predictable path. The implementation that provides all this is `dsh-bash-local`; the model-facing `bash`/`bash_output`/`bash_kill` schemas that call it are in `dsh-tool-bash` (and present as terminals via the [tool-presentation vocabulary](tools.md#tool-presentation-ui-vocabulary)).
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