deepseek-harness/docs/subsystems/tasks.md

Background Task Runtime

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Types shared by long-running producers, ctx.tasks, and task control surfaces. The runtime Agent Note owns the design; this page records the literal shapes from packages/tasks/tasks/src/types.ts.

Ids and status

TaskId is a branded id generated as <kind>-N. Access control relies on owner authorization, not id secrecy. TaskKind derives from a merge-extensible map; the registry treats kinds as opaque id namespaces.

/**
 * Producer-defined task kinds. Plugins extend this map by declaration merging;
 * the registry treats every value as an opaque id namespace.
 */
interface TaskKindMap {
  bash: 'bash'
  subagent: 'subagent'
}

TaskStatus is 'running' | 'stopping' | 'completed' | 'killed' | 'failed'; producer-specific facts belong in TaskSnapshot.detail.

Producer contract

TaskStart declares identity and a starter. The runtime finishes preflight before calling run() and commits without a later failable step. Producers own execution resources; the runtime owns identity, access, and lifecycle state.

/**
 * Producer declaration passed to {@link TaskService.start}. The runtime
 * preflights access and cleanup before invoking {@link run}; the producer owns
 * execution resources while the runtime owns identity and lifecycle state.
 */
interface TaskStart {
  /** Producer kind — also the id prefix (`bash`, `subagent`, …). */
  kind: TaskKind
  /** One-line model-facing label (the command; the delegation description). */
  label: string
  /**
   * Optional UTF-8 byte cap for each complete model-facing completion notice or
   * output read, including control-surface status metadata.
   */
  outputLimitBytes?: number
  /**
   * Owning live agent. Access is fenced by its session id, and agent disposal
   * cancels and awaits the task. The instance must be the one currently
   * registered under its agent id. Omitting the owner creates an unowned task,
   * open to any caller until service disposal.
   */
  owner?: Agent
  /**
   * Start the work after preflight and synchronously return its hooks. Called
   * once; a throw leaves nothing registered, and the producer must clean up any
   * partially started resources.
   */
  run(): TaskHooks
}

TaskHooks.done is the quiescence boundary. Optional readOutput distinguishes consuming stream tasks from final-output-only tasks.

/** Hooks through which the runtime controls and observes producer work. */
interface TaskHooks {
  /**
   * Request termination. Must be synchronous, idempotent, and eventually settle
   * {@link done}; throws propagate. The optional reason is forwarded verbatim.
   */
  cancel(reason?: string): void
  /**
   * Resolves after the producer releases its resources, not merely when work
   * finishes. Must not reject; the runtime converts a rejection to `failed`.
   * If teardown cancellation throws, the runtime may force-fail only the
   * registry record without claiming that the work stopped.
   */
  done: Promise<TaskOutcome>
  /**
   * Consume output produced since the previous call. The producer formats
   * truncation and spill notices. Absence marks a final-output-only task; each
   * task has one consuming cursor.
   */
  readOutput?(): string
}

/** Terminal result supplied by a producer through {@link TaskHooks.done}. */
interface TaskOutcome {
  /** How the task ended: finished (`completed`), cancelled (`killed`), or broke (`failed`). */
  status: 'completed' | 'killed' | 'failed'
  /** Kind-specific detail rendered into status lines ('exit code: 3', 'max-tokens'). */
  detail?: string
  /** Final output for tasks without `readOutput`; stream tasks leave it unset. */
  output?: string
}

Consumer views

Snapshots are fresh read-only projections. ownerSession carries the shared SessionId used for authorization; completion listeners separately receive the exact owner object used for lifecycle cleanup. reported suppresses a completion notice after another surface has delivered or committed to deliver the terminal state.

/**
 * A read-only projection of one task, safe to hand to listeners and tools —
 * a fresh object per call, never live registry state.
 */
interface TaskSnapshot {
  /** The registry-issued id (`<kind>-N`). */
  id: TaskId
  /** The producer kind the task was registered with. */
  kind: TaskKind
  /** The producer-supplied one-line label. */
  label: string
  /** Producer-owned cap for complete model-facing notices and output reads. */
  outputLimitBytes?: number
  /**
   * Owner session id used for authorization and correlation; absent for
   * unowned tasks. Completion listeners receive the exact {@link Agent}
   * separately through {@link TaskDoneListener}.
   */
  ownerSession?: SessionId
  /** Current lifecycle state. */
  status: TaskStatus
  /** Kind-specific status detail, present once the producer supplied one (usually terminal). */
  detail?: string
  /** Epoch ms when the task was registered. */
  startedAt: number
  /** Epoch ms when the task settled; absent while `running`/`stopping`. */
  finishedAt?: number
  /**
   * True when a kill, read, or wait has reported or committed to report the
   * terminal state. Completion surfaces suppress redundant notices when set.
   */
  reported: boolean
}

/** Output and post-read state returned by {@link TaskService.read}. */
interface TaskRead {
  /**
   * Stream kinds: the consuming delta since the previous read. Final-output
   * kinds: empty while live, the terminal {@link TaskOutcome.output} (or
   * empty) once settled — idempotent, never consumed.
   */
  text: string
  /** The task's state at read time. */
  snapshot: TaskSnapshot
}

Service behavior

The abstract TaskService Service Definition specifies atomic start, caller-scoped get and list, read, kill, bounded wait, contained onTaskDone and onTasksChanged listeners, and the attachSurface availability fence; LocalTaskService is the process-local provider. The two listener kinds are not nested: onTaskDone delivers one terminal record under first-wins semantics a control surface couples to notice delivery, while onTasksChanged observes every visible-set change — registration, the stopping transition, settlement, and owner-disposal removal — carrying only the owner whose set moved, or undefined when an unowned task changed and every caller's set moved with it. Authorization compares owner sessions; owner cleanup selects the exact registered Agent instance. See dsh-tasks for the Service Definition contract, dsh-tasks-local for the registry lifecycle, and dsh-tool-tasks for the model-facing Consumer.

Cordis surface

Generated from source by scripts/gen-cordis-catalog.ts (verified fresh by pnpm run verify-cordis-catalog in doc-sync; regenerate with pnpm run gen-cordis-catalog) — this section is byte-identical in both language sides of the page. Signature blocks use a ts cordis-catalog fence and keep the original source JSDoc; dispatch modes are defined in the primer, and the framework-inherited ctx surface lives in cordis-api/inherited.md.

ctx.tasks — TaskService (abstract seam)

Abstract background task registry. Subclass, implement the abstract methods, and load the subclass as a plugin — it registers as ctx.tasks (one implementation per context; loading a second throws, which is cordis' standard duplicate-service behavior).

Implementations must honor these semantics:

• Registrations outlive producer and control-surface fibers. Owner and service disposal cancel live work and await compliant producers; a throwing teardown cancel force-fails only the record.
• Owned-task access is fenced by the owner's session id. Ids are predictable, so authorization — not secrecy — is the boundary.
• Settlement is first-wins: one terminal record, one round of contained listener notification, and released waiters, even against a late producer outcome.
• start refuses work while no control surface is attached, so a producer cannot start work that callers cannot collect or stop.

/**
 * Preflight access, validation, and owner cleanup before starting and
 * atomically registering work. A throwing starter leaves nothing registered;
 * after it returns, registration cannot fail. Settlement records the outcome,
 * notifies listeners, and releases waiters.
 * @param spec - task identity, owner, and synchronous starter.
 * @returns the registry-issued `<kind>-N` id.
 */
abstract start(spec: TaskStart): TaskId

/**
 * List caller-owned and unowned tasks in registration order without exposing
 * another session's labels.
 * @param caller - reading agent; a non-agent caller sees only unowned tasks.
 * @returns fresh snapshots.
 */
abstract list(caller?: Agent): TaskSnapshot[]

/**
 * Return a non-consuming snapshot without changing its read cursor or notice
 * state. Throws for an unknown or foreign task.
 * @param id - task to look up.
 * @param caller - reading agent checked against the owner.
 * @returns a fresh snapshot.
 */
abstract get(id: TaskId, caller?: Agent): TaskSnapshot

/**
 * Read the next stream delta, or the idempotent final output after settlement.
 * A terminal read marks the task reported. Throws for an unknown or foreign
 * task.
 * @param id - task to read.
 * @param caller - reading agent checked against the owner.
 * @returns output text and the post-read snapshot.
 */
abstract read(id: TaskId, caller?: Agent): TaskRead

/**
 * Request cancellation, then mark the task stopping and reported. A producer
 * throw propagates without changing task state. Throws for an unknown or
 * foreign task.
 * @param id - task to cancel.
 * @param caller - killing agent checked against the owner.
 * @param reason - logged reason forwarded to the producer.
 * @returns `requested` for live work, otherwise `already-finished`.
 */
abstract kill(id: TaskId, caller?: Agent, reason?: string): 'requested' | 'already-finished'

/**
 * Wait for settlement or timeout without cancelling the task. Caller abort
 * rejects only while the task is live; after settlement the terminal
 * snapshot wins so a notice suppressed for this waiter is still delivered.
 * Throws for invalid, unknown, or foreign input.
 * @param id - task to wait for.
 * @param timeoutMs - positive finite wait bound in milliseconds.
 * @param caller - waiting agent checked against the owner.
 * @param signal - optional cancellation of the wait itself.
 * @returns snapshot at settlement or timeout.
 */
abstract wait(id: TaskId, timeoutMs: number, caller?: Agent, signal?: AbortSignal): Promise<TaskSnapshot>

/**
 * Register an effect-scoped completion listener. Each listener is contained;
 * returned promises are observed but not awaited. No listener runs after
 * service disposal.
 * @param listener - receives each terminal snapshot and its exact owner.
 * @returns disposer that unregisters the listener.
 */
abstract onTaskDone(listener: TaskDoneListener): () => void

/**
 * Register an effect-scoped observer of visible-set changes. It fires after
 * every commit that changes what {@link list} returns for that owner —
 * registration, every stopping transition (including the one teardown
 * performs before it awaits a slow producer), settlement, owner-disposal
 * removal, and the emptying that service disposal commits — so an observer
 * re-reads rather than accumulating deltas.
 *
 * The registration binds to the CALLING fiber, so an observer mounted outside
 * this service still receives the disposal emptying; that is what stops a
 * consumer from retaining rows after the registry unloads.
 *
 * This is not a superset of {@link onTaskDone}: that one delivers the terminal
 * record under first-wins semantics a control surface couples to notice
 * delivery, while this one carries no delivery meaning and marks nothing
 * reported. Listeners are contained and never awaited.
 * @param listener - receives the owner whose visible set changed, or
 *   `undefined` when an unowned task changed and every caller's set did.
 * @returns disposer that unregisters the listener.
 */
abstract onTasksChanged(listener: TasksChangedListener): () => void

/**
 * Attach an effect-scoped surface that can read and stop tasks. {@link start}
 * refuses work while none is attached.
 * @param name - diagnostic label; duplicate names remain independent.
 * @returns disposer that detaches this surface.
 */
abstract attachSurface(name: string): () => void

Types: Agent

Source: packages/tasks/tasks/src/index.ts:53