deepseek-harness/packages/bash/tool-bash/src/index.ts

/**
 * Model-facing `bash`, `bash_output`, and `bash_kill` tools over the executor
 * seam. Background tasks are fenced by owning session, completion injects a
 * durable notice, and confining executors add one-shot approval-based escalation.
 * Notices do not wake idle agents. Ownership is stored with the executor task so
 * it survives this plugin's reload; per-call authority is escalation grant,
 * session override, then executor default. See the package README for the tool contract.
 * @module @deepseek-ai/dsh-tool-bash
 */

import { Service, type Context } from 'cordis'
import z from 'schemastery'
import { isAbsolute, resolve as resolvePath } from 'node:path'
import { defineTool } from '@deepseek-ai/dsh-tools'
import type { GenericCallView, TerminalCallView, ToolExecution, ToolResult, ToolResultView } from '@deepseek-ai/dsh-tools'
import type { Agent } from '@deepseek-ai/dsh-agent'
import type {} from '@deepseek-ai/dsh-session-persistence'
import { assertNever } from '@deepseek-ai/dsh-llm'
import type {} from '@deepseek-ai/dsh-system-prompt'
// Side-effect type import: declaration-merges `ctx.approval`, consumed
// opportunistically by the escalation gate (`ctx.get('approval')` — the seam
// stays optional at runtime, same pattern as dsh-tools' ask routing).
import type {} from '@deepseek-ai/dsh-user-approval'
import type { SandboxMode } from '@deepseek-ai/dsh-sandbox'
import { BashTaskId, DSH_ENV_PREFIX, OwnerToken, effectiveSandboxMode } from '@deepseek-ai/dsh-bash'
import type { BashTask, DshEnvironment, DshEnvironmentKey } from '@deepseek-ai/dsh-bash'
import { DSH_HOME_ENV, resolveDshHome } from '@deepseek-ai/dsh-home'
import { parseExitStatus, renderResult } from './render.ts'

declare module 'cordis' {
  interface Context {
    bashEnv: BashEnvRegistry
  }
}

export const name = 'tool-bash'
export const inject = ['tools', 'bash', 'systemPrompt']

/** Configuration for the bash tool and its managed child environment. */
export interface Config {
  /** DeepSeek Harness home directory exposed as `DSH_HOME`; defaults to `$DSH_HOME` or `~/.dsh`. */
  dshHome?: string
}

/** Runtime configuration schema for the bash tool plugin. */
export const Config: z<Config> = z.object({
  dshHome: z.string(),
})

/** Model-visible metadata for one managed `DSH_*` environment variable. */
export interface BashEnvVariable {
  /** Concise description of the environment fact represented by the variable. */
  description: string
}

/**
 * A plugin contribution to the managed environment of each model bash call.
 * Declared keys make ownership conflicts detectable before the first command;
 * `resolve` computes only the values available for the current execution.
 */
export interface BashEnvContributor {
  /** Stable contributor name used in diagnostics and duplicate detection. */
  name: string
  /** Complete set of `DSH_*` keys this contributor may return. */
  variables: Readonly<Record<DshEnvironmentKey, BashEnvVariable>>
  /**
   * Resolve this contributor's available values for one tool execution.
   * @param execution - the bash tool execution and its optional calling agent.
   * @returns a partial map containing only keys declared in {@link variables}.
   */
  resolve(execution: ToolExecution): Readonly<Partial<Record<DshEnvironmentKey, string>>>
}

/** An enumerable declaration returned by {@link BashEnvRegistry.list}. */
export interface BashEnvVariableInfo extends BashEnvVariable {
  /** Contributor that owns the variable. */
  contributor: string
  /** Declared `DSH_*` environment variable name. */
  key: DshEnvironmentKey
}

const DSH_SHELL_KEY = `${DSH_ENV_PREFIX}SHELL` as const
const DSH_SESSION_ID_KEY = `${DSH_ENV_PREFIX}SESSION_ID` as const
const DSH_SESSION_JSONL_KEY = `${DSH_ENV_PREFIX}SESSION_JSONL` as const
const RESERVED_BASH_ENV_KEYS = new Set<DshEnvironmentKey>([
  DSH_HOME_ENV,
  DSH_SHELL_KEY,
  DSH_SESSION_ID_KEY,
])
const BASH_ENV_KEY_SUFFIX = /^[A-Z][A-Z0-9_]*$/

/**
 * Registry (`ctx.bashEnv`) for trusted, per-execution `DSH_*` variables.
 * The namespace is rebuilt for every model bash call: ambient `DSH_*` values
 * are discarded by the executor, then the registry's current snapshot is
 * injected. Built-in shell facts remain owned by the registry itself while
 * plugins can register additional, enumerable facts with effect-scoped
 * disposal.
 */
export class BashEnvRegistry extends Service {
  private readonly contributors = new Map<string, BashEnvContributor>()
  private readonly keyOwners = new Map<DshEnvironmentKey, string>()
  private readonly dshHome: string

  /**
   * Create and install the `ctx.bashEnv` service.
   * @param ctx - Cordis context that owns the service and registrations.
   * @param config - home-directory configuration for the built-in variables.
   */
  constructor(ctx: Context, config: Config = {}) {
    super(ctx, 'bashEnv')
    this.dshHome = resolveDshHome(config.dshHome)
  }

  /**
   * Register one environment contributor. Names and keys are unique; built-in
   * keys are reserved. Registration is disposed with the calling plugin fiber.
   * @param contributor - declared key ownership and per-execution resolver.
   * @returns the disposer that unregisters the contribution.
   */
  register(contributor: BashEnvContributor): () => void {
    const dispose = this.ctx.effect(function* (this: BashEnvRegistry) {
      if (contributor.name.trim().length === 0) {
        throw new Error('bash env contributor name must be non-empty')
      }
      if (this.contributors.has(contributor.name)) {
        throw new Error(`bash env contributor "${contributor.name}" is already registered`)
      }

      const variables = Object.entries(contributor.variables) as [DshEnvironmentKey, BashEnvVariable][]
      for (const [key, variable] of variables) {
        if (!key.startsWith(DSH_ENV_PREFIX)
          || !BASH_ENV_KEY_SUFFIX.test(key.slice(DSH_ENV_PREFIX.length))) {
          throw new Error(`bash env contributor "${contributor.name}" declared invalid key "${key}"`)
        }
        if (RESERVED_BASH_ENV_KEYS.has(key)) {
          throw new Error(`bash env contributor "${contributor.name}" cannot own reserved key "${key}"`)
        }
        if (variable.description.trim().length === 0) {
          throw new Error(`bash env contributor "${contributor.name}" must describe "${key}"`)
        }
        const owner = this.keyOwners.get(key)
        if (owner !== undefined) {
          throw new Error(`bash env key "${key}" is already owned by contributor "${owner}"; contributor "${contributor.name}" cannot also own it`)
        }
      }

      this.contributors.set(contributor.name, contributor)
      for (const [key] of variables) this.keyOwners.set(key, contributor.name)
      yield () => {
        this.contributors.delete(contributor.name)
        for (const [key] of variables) this.keyOwners.delete(key)
      }
    }.bind(this), 'bashEnv.register()')
    return () => void dispose()
  }

  /**
   * Build the trusted `DSH_*` snapshot for one bash tool execution.
   * @param execution - the current tool execution.
   * @returns an immutable environment overlay containing built-ins and current contributions.
   */
  collect(execution: ToolExecution): DshEnvironment {
    const values: Record<DshEnvironmentKey, string> = {
      [DSH_HOME_ENV]: this.dshHome,
      [DSH_SHELL_KEY]: '1',
    }
    if (execution.agent !== undefined) {
      values[DSH_SESSION_ID_KEY] = execution.agent.session.header.id
    }

    for (const contributor of [...this.contributors.values()].sort((left, right) => left.name.localeCompare(right.name))) {
      const resolved = contributor.resolve(execution)
      for (const [rawKey, value] of Object.entries(resolved)) {
        const key = rawKey as DshEnvironmentKey
        if (!Object.hasOwn(contributor.variables, key)) {
          throw new Error(`bash env contributor "${contributor.name}" returned undeclared key "${key}"`)
        }
        if (typeof value !== 'string') {
          throw new Error(`bash env contributor "${contributor.name}" returned a non-string value for "${key}"`)
        }
        values[key] = value
      }
    }

    return Object.freeze(Object.fromEntries(Object.entries(values).sort(([left], [right]) => left.localeCompare(right))))
  }

  // TODO(bash-env-list-builtins): Include registry-owned built-ins before diagnostics,
  // prompt, or UI code treats list() as an exhaustive environment catalog.
  /**
   * Enumerate plugin-contributed variables without executing their resolvers.
   * @returns declarations sorted by environment variable name.
   */
  list(): BashEnvVariableInfo[] {
    return [...this.contributors.values()]
      .flatMap(contributor => Object.entries(contributor.variables).map(([key, variable]) => ({
        contributor: contributor.name,
        description: variable.description,
        key: key as DshEnvironmentKey,
      })))
      .sort((left, right) => left.key.localeCompare(right.key))
  }
}

/**
 * Validate value constraints absent from SchemaSpec: non-empty strings, a
 * positive finite timeout, and paired escalation mode and justification.
 */
function validateBashArgs(args: BashToolArgs): void {
  if (args.command.trim().length === 0) {
    throw new Error('invalid command: expected a non-empty string')
  }
  if (args.description.trim().length === 0) {
    throw new Error('invalid description: expected a non-empty string')
  }
  if (args.timeoutMs !== undefined && (!Number.isFinite(args.timeoutMs) || args.timeoutMs <= 0)) {
    throw new Error(`invalid timeoutMs: expected a positive number, got ${JSON.stringify(args.timeoutMs)}`)
  }
  if (args.sandbox_permissions !== undefined && args.justification === undefined) {
    throw new Error('invalid escalation: sandbox_permissions requires a justification')
  }
  if (args.justification !== undefined && args.sandbox_permissions === undefined) {
    throw new Error('invalid escalation: justification is only valid together with sandbox_permissions')
  }
  if (args.justification !== undefined && args.justification.trim().length === 0) {
    throw new Error('invalid justification: expected a non-empty sentence')
  }
}

/**
 * Reject an empty `task_id`; SchemaSpec already validates type and presence.
 */
function validateTaskId(value: string): BashTaskId {
  if (value.length === 0) {
    throw new Error(`invalid task_id: expected a string, got ${JSON.stringify(value)}`)
  }
  return BashTaskId(value)
}

/**
 * Validated bash arguments. Escalation fields are advertised only when the
 * mounted executor reports a confining mode.
 */
interface BashToolArgs {
  command: string
  description: string
  timeoutMs?: number
  workdir?: string
  run_in_background?: boolean
  sandbox_permissions?: string
  justification?: string
}

/**
 * Strictly wider modes for each effective mode. Execution checks this table
 * because the schema is global while the effective mode is per call.
 */
const WIDER_MODES: Record<string, readonly SandboxMode[]> = {
  'read-only': ['workspace-write', 'danger-full-access'],
  'workspace-write': ['danger-full-access'],
}

/**
 * All possible escalation targets. Advertise the global set because a session
 * override may be narrower than the executor default; execution rejects a
 * target that is not wider for that call.
 */
const ESCALATION_TARGETS: readonly SandboxMode[] = ['workspace-write', 'danger-full-access']

/**
 * The bash tool's byte-stable base description. Escalation guidance is added
 * only when the mounted executor can honor it, as the one exception to the
 * ordinary no-retry guidance.
 */
function bashDescription(escalationModes: readonly SandboxMode[]): string {
  const base = 'Execute a bash command (`bash -c`) and return its stdout/stderr. '
    + 'Each call runs in a fresh shell: no state (cwd, variables, functions) persists between calls — '
    + 'pass `workdir` instead of using `cd`. Non-zero exits are reported as `[exit code: N]`. '
    + `Current harness environment facts are exposed through managed \`$${DSH_ENV_PREFIX}*\` variables; inspect them when needed. `
    + 'Commands may run under a file sandbox; a blocked file operation is reported as `[sandbox: file access denied under <mode> mode]` — a policy denial, not a bug in the command; do not retry another way (a background task reports the same marker via bash_output once it has finished). '
    + 'Long output is truncated to its tail; the full output is saved to a file whose path is reported when available. '
    + 'Set `run_in_background: true` for long-running commands: the call returns a task id immediately; '
    + 'poll it with `bash_output` and stop it with `bash_kill`.'
  if (escalationModes.length === 0) return base
  return base + ' Attempting a command the sandbox may deny is safe and expected: run it and read the '
    + 'marker rather than assuming the denial. When a command is denied and a wider mode would let it '
    + 'succeed, escalate immediately in the same turn — the one sanctioned exception to a denial: retry '
    + 'the exact same command once with `sandbox_permissions` (the narrowest wider mode that suffices) '
    + 'plus a one-sentence `justification`. Do not detour through chat to ask permission first — the '
    + 'approval prompt raised by that retry is how the user consents. If the session states approval '
    + 'prompts are disabled, there is no exception: a denial is final — do not set `sandbox_permissions`. '
    + 'Never escalate speculatively: ground the request in a real denial — normally the one this command '
    + 'just hit; escalating up front is fine only when this session already denied the same access. '
    + 'A rejected escalation is final for that command — stop and explain, never work around '
    + 'it — but it does not forbid attempting or escalating other commands later.'
}

// Pure tool-owned presentation used for both live events and replay.

/**
 * Present foreground calls as terminals and background starts as generic cards.
 */
type BashCallArgs = { command: string; description: string; workdir?: string; run_in_background?: boolean }

function presentBashCall(args: BashCallArgs): GenericCallView | TerminalCallView {
  // A background start is not an interactive terminal — a generic execute card
  // with the command as rawInput and the description as a content block.
  if (args.run_in_background === true) {
    return {
      card: 'generic',
      title: args.command,
      kind: 'execute',
      rawInput: args.command,
      content: [{ type: 'text', text: args.description }],
    }
  }
  // A foreground run is a terminal; an explicit workdir supplies its cwd.
  return {
    card: 'terminal',
    title: args.command,
    description: args.description,
    ...args.workdir !== undefined ? { cwd: args.workdir } : {},
  }
}

/**
 * Present completed foreground output as a terminal; background acknowledgements
 * and execution errors use generic fenced output without an exit-status pill.
 */
function presentBashResult(args: unknown, result: ToolResult): ToolResultView | undefined {
  const block = result.content.length === 1 ? result.content[0] : undefined
  if (block === undefined || block.type !== 'text') return undefined
  const raw = block.text
  const isBackground = typeof args === 'object' && args !== null && (args as { run_in_background?: unknown }).run_in_background === true
  // A background ack or an errored run is not a real terminal exit: render the
  // fenced ```console fallback as generic content (no exit pill).
  if (isBackground || result.isError) {
    return { card: 'generic', content: [{ type: 'text', text: `\`\`\`console\n${raw.replace(/\n+$/, '')}\n\`\`\`` }] }
  }
  // A finished foreground run supplies raw output and parsed exit status.
  // The bridge derives the no-capability fenced fallback from `output`.
  return { card: 'terminal', output: raw, ...parseExitStatus(raw) }
}

/** Pending-state presentation for `bash_output`/`bash_kill` (background-task tools). */
function presentTaskCall(verb: string, args: { task_id: string }): GenericCallView {
  return { card: 'generic', title: `${verb} background task ${args.task_id}`, kind: 'execute', rawInput: args.task_id }
}

/**
 * Resolve an explicit workdir first, making a relative one session-cwd-relative;
 * otherwise use the session cwd and leave executor defaulting as the fallback.
 */
function resolveWorkdir(modelWorkdir: string | undefined, exec: { agent?: Agent }): string | undefined {
  const sessionCwd = exec.agent?.session.header.cwd
  if (modelWorkdir === undefined) return sessionCwd
  if (sessionCwd !== undefined && !isAbsolute(modelWorkdir)) {
    return resolvePath(sessionCwd, modelWorkdir)
  }
  return modelWorkdir
}

/** Status line for background task reads. */
function statusLine(task: BashTask): string {
  switch (task.status) {
    case 'running': return '[status: running]'
    case 'killed': return `[status: killed${task.signal !== null ? ` by ${task.signal}` : ''}]`
    case 'completed': return `[status: completed, exit code: ${task.exitCode ?? 0}]`
  }
}

export function apply(ctx: Context, config: Config = {}): void {
  const bashEnv = new BashEnvRegistry(ctx, config)
  bashEnv.register({
    name: 'session-persistence',
    variables: {
      [DSH_SESSION_JSONL_KEY]: {
        description: 'Absolute target path of the current session JSONL when the active persistence backend provides one.',
      },
    },
    resolve(execution) {
      const agent = execution.agent
      if (agent === undefined) return {}
      const location = ctx.get('sessionPersistence')?.locate(agent.session.header)
      return location?.kind === 'jsonl' ? { [DSH_SESSION_JSONL_KEY]: location.path } : {}
    },
  })

  // Cross-call guidance belongs in the prompt rather than one tool description.
  ctx.systemPrompt.section({
    name: 'tool:bash',
    order: 105,
    text: 'Check the [exit code: N] marker on every bash result; investigate failures before moving on.',
  })

  /**
   * Return the canonical session-header id used by ACP and persistence as the
   * task owner, or undefined for a non-agent caller.
   */
  const callerToken = (exec: { agent?: Agent }): OwnerToken | undefined =>
    exec.agent ? OwnerToken(exec.agent.session.header.id) : undefined

  /**
   * Reject access when a task has a different session owner. Unowned tasks are
   * allowed; unknown ids still fail in the subsequent read or kill.
   */
  const assertTaskAccess = (taskId: BashTaskId, exec: { agent?: Agent }): void => {
    const owner = ctx.bash.ownerOf(taskId)
    if (owner !== undefined && owner !== callerToken(exec)) {
      throw new Error(`task ${taskId} belongs to another session`)
    }
  }

  // Completion runs on the bash fiber, so use topology-independent lookup and
  // match the executor's stored session-owner token to a live agent.
  ctx.bash.onTaskDone((task) => {
    const ownerToken = ctx.bash.ownerOf(task.id)
    if (ownerToken === undefined) return
    const agent = ctx.get('agents')?.list().find(a => OwnerToken(a.session.header.id) === ownerToken)
    if (!agent) return
    try {
      agent.inject(
        [{ type: 'text', text: `background bash task ${task.id} finished ${statusLine(task)}. Read its output with bash_output.` }],
        { source: { kind: 'plugin', plugin: 'tool-bash' } },
      )
    } catch (error: unknown) {
      // The one expected failure: the agent was disposed between task completion and this
      // injection (ReactLoopAgent.inject throws `agent "<id>" is disposed`).
      if (error instanceof Error && error.message.includes('is disposed')) return
      throw error
    }
  })

  // The escalation surface exists whenever the mounted executor confines.
  // Advertise the closed target vocabulary globally, then enforce strict
  // widening against each call's effective session mode.
  const defaultMode = ctx.bash.sandboxMode
  const escalationModes: readonly SandboxMode[] = defaultMode === undefined ? [] : ESCALATION_TARGETS

  /**
   * Return the calling session's folded standing mode. Approval outranks this
   * value and the executor default applies when it is absent; non-sandboxing
   * and agent-less calls have no override.
   */
  const sessionOverride = (exec: ToolExecution): SandboxMode | undefined =>
    defaultMode === undefined || exec.agent === undefined ? undefined : effectiveSandboxMode(exec.agent.session.events)

  /**
   * Request one-shot escalation before execution. Missing approval context,
   * rejection, cancellation, and unavailable answers throw without running the
   * command; the optional seam is resolved per call through `ctx.get`.
   */
  const approveEscalation = async (mode: string, justification: string, exec: ToolExecution): Promise<SandboxMode> => {
    // Reject an unadvertised escalation before prompting for a nonexistent sandbox.
    if (escalationModes.length === 0) {
      throw new Error('sandbox_permissions is not available in this composition (no sandboxing executor to escalate)')
    }
    // Reject sandbox widening against the call's effective mode before requesting approval.
    const effectiveMode = (sessionOverride(exec) ?? defaultMode) as SandboxMode
    if (!(WIDER_MODES[effectiveMode] ?? []).includes(mode as SandboxMode)) {
      throw new Error(`sandbox escalation to "${mode}" is not strictly wider than this call's current "${effectiveMode}" mode`)
    }
    const approval = ctx.get('approval')
    if (approval === undefined) {
      throw new Error(`sandbox escalation to "${mode}" requires approval, but no approval service is composed`)
    }
    if (exec.agent === undefined) {
      throw new Error(`sandbox escalation to "${mode}" requires approval, but the call has no agent to route it through`)
    }
    const outcome = await approval.request({
      agent: exec.agent,
      toolName: 'bash',
      callId: exec.callId,
      // Self-contained for the audit trail: approval/asked stores this
      // reason, and the target mode is part of the grant's identity.
      reason: `escalate sandbox to ${mode}: ${justification}`,
      ...exec.signal ? { signal: exec.signal } : {},
    })
    switch (outcome) {
      // Schema validation pins the vocabulary; the per-call check proves widening.
      case 'allowed-once': return mode as SandboxMode
      case 'rejected': throw new Error(`the user rejected escalating this command to "${mode}"`)
      case 'cancelled': throw new Error(`approval for escalating to "${mode}" was cancelled`)
      case 'unavailable': throw new Error(`sandbox escalation to "${mode}" requires approval, but no approval channel is available`)
      default: return assertNever(outcome, 'ApprovalOutcome')
    }
  }

  ctx.tools.register(defineTool({
    name: 'bash',
    description: bashDescription(escalationModes),
    parameters: {
      command: { type: 'string', required: true, description: 'The bash command to execute.' },
      description: {
        type: 'string',
        required: true,
        description: 'Clear, concise description of what this command does in active voice, '
          + '5-10 words (shown in the UI). Examples: "ls" → "List files in current directory"; '
          + '"git status" → "Show working tree status"; "npm install" → "Install package dependencies".',
      },
      timeoutMs: { type: 'number', description: 'Timeout in milliseconds. The executor applies its configured default and cap, and kills the command on expiry.' },
      workdir: { type: 'string', description: 'Working directory for this command. Defaults to the session workspace; a relative path is resolved against it.' },
      run_in_background: { type: 'boolean', description: 'Run in the background and return a task id immediately. No timeout applies.' },
      ...escalationModes.length > 0 ? {
        sandbox_permissions: {
          type: 'string' as const,
          enum: [...escalationModes],
          description: 'The wider sandbox mode this command needs. Only valid as a one-shot retry '
            + 'of a command the sandbox just denied; requires justification and user approval.',
        },
        justification: {
          type: 'string' as const,
          description: 'Required with sandbox_permissions: one sentence for the user explaining '
            + 'why this exact command needs the wider access.',
        },
      } : {},
    },
    async execute(args: BashToolArgs, exec) {
      validateBashArgs(args)
      // `description` is display/logging metadata only. Escalation approval
      // completes before execution; grant > session override > executor default.
      const sandboxMode = args.sandbox_permissions !== undefined && args.justification !== undefined
        ? await approveEscalation(args.sandbox_permissions, args.justification, exec)
        : sessionOverride(exec)
      // Default the workdir to the calling agent's session cwd so each ACP
      // session runs in its own workspace (see resolveWorkdir); an explicit
      // model workdir still wins.
      const workdir = resolveWorkdir(args.workdir, exec)
      const dshEnv = bashEnv.collect(exec)
      const request = {
        command: args.command,
        ...workdir !== undefined ? { workdir } : {},
        ...args.timeoutMs !== undefined ? { timeoutMs: args.timeoutMs } : {},
        ...exec.signal ? { signal: exec.signal } : {},
        dshEnv,
        ...sandboxMode !== undefined ? { sandboxMode } : {},
      }
      if (args.run_in_background === true) {
        // Store the session owner on the task for bash_output/bash_kill isolation.
        const task = ctx.bash.start(ctx.bash.resolve({ ...request, owner: callerToken(exec) }))
        return [{ type: 'text', text: `started background task ${task.id}` }]
      }
      const result = await ctx.bash.run(ctx.bash.resolve(request))
      if (result.aborted) throw new Error('command aborted')
      return [{ type: 'text', text: renderResult(result, escalationModes) }]
    },
    presentCall: presentBashCall,
    presentResult: presentBashResult,
  }))

  ctx.tools.register(defineTool({
    name: 'bash_output',
    description: 'Read new output from a background bash task started with `bash` + `run_in_background`. '
      + 'Returns only output produced since the previous bash_output call, plus the task status. '
      + 'Tasks keep running while you do other work; poll again later for more output.',
    parameters: {
      task_id: { type: 'string', required: true, description: 'Task id returned by the bash tool.' },
    },
    // execute is synchronous (registry reads + string shaping) but the
    // ToolDefinition contract wants a Promise — hence resolve(), not async.
    execute(args, exec) {
      const id = validateTaskId(args.task_id)
      assertTaskAccess(id, exec)
      const read = ctx.bash.readOutput(id)
      let text = read.delta.length > 0 ? read.delta : '(no new output)'
      if (read.lossy) {
        const paths = [read.stdoutSpillPath, read.stderrSpillPath].filter((p): p is string => p !== undefined)
        const fullOutput = paths.length > 0 ? paths.join(', ') : '(unavailable)'
        text += `\n[some output was dropped from memory; full output: ${fullOutput}]`
      }
      text += `\n${statusLine(read.task)}`
      if (read.task.sandbox?.runnerFailed) {
        // Background settlement carries the runner-failure fact that a
        // foreground call exposes as SANDBOX_UNAVAILABLE.
        text += `\n[sandbox: the sandbox runner itself failed under ${read.task.sandbox.mode} mode — the command did not run; this is a sandbox problem, not a command failure]`
      } else if (read.task.sandbox?.denied) {
        // Mirrors the foreground result marker (and its same-turn escalation hint).
        text += `\n[sandbox: file access denied under ${read.task.sandbox.mode} mode]`
        if (escalationModes.length > 0) {
          text += '\n[sandbox: escalation available — retry this exact command once with sandbox_permissions (the narrowest wider mode that suffices) + justification; the approval prompt asks the user]'
        }
      }
      return Promise.resolve([{ type: 'text', text }])
    },
    presentCall: args => presentTaskCall('Read output from', args),
  }))

  ctx.tools.register(defineTool({
    name: 'bash_kill',
    description: 'Ask the executor to kill a running background bash task by task id.',
    parameters: {
      task_id: { type: 'string', required: true, description: 'Task id returned by the bash tool.' },
    },
    execute(args, exec) {
      const id = validateTaskId(args.task_id)
      assertTaskAccess(id, exec)
      const killed = ctx.bash.kill(id)
      return Promise.resolve([{
        type: 'text',
        text: killed ? `killed background task ${id}` : `task ${id} had already finished`,
      }])
    },
    presentCall: args => presentTaskCall('Kill', args),
  }))
}