Task Engine Error Types (task-engine/errors.ts)

Defines discriminated custom error classes for the task engine, covering not‑found, invalid transitions, version conflicts, and unknown fields, enabling precise error handling and retry logic.

// Source: https://github.com/FarzamMohammadi/the-engineer | License: MIT | Copyright 2026 Farzam Mohammadi
// Provided via justclaw.it.com; keep this notice with the code.
/** Base class for all task-engine errors. Tagged for discriminated matching. */
export abstract class TaskEngineError extends Error {
  abstract readonly tag: string;
  abstract readonly retryable: boolean;
}

/** Task was not found by ID. */
export class TaskNotFoundError extends TaskEngineError {
  readonly tag = "TaskNotFound" as const;
  readonly retryable = false;
  readonly taskId: string;

  constructor(taskId: string) {
    super(`Task "${taskId}" not found`);
    this.name = "TaskNotFoundError";
    this.taskId = taskId;
  }
}

/** State transition is not valid per the state machine. */
export class InvalidTra

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