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These errors surface from the task-augmented tool invocation system (per the MCP 2025-11-25 task-support protocol). All inherit from PublicMcpError (safe to surface to clients) except TaskStoreNotInitializedError.

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Reference

ClassInheritsJSON-RPC CodeWhen
TaskNotFoundErrorPublicMcpError-32602tasks/get, tasks/cancel, or tasks/result referenced an unknown task ID
TaskAlreadyTerminalErrorPublicMcpError-32602tasks/cancel invoked on a task already in succeeded/failed/cancelled
TaskAugmentationNotSupportedErrorPublicMcpError-32601Client invoked tools/call with task augmentation on a tool that opts out
TaskAugmentationRequiredErrorPublicMcpError-32601Tool declared taskSupport: 'required' but client did not request a task
TaskStoreNotInitializedErrorInternalMcpError—Internal: task store provider not registered when task subsystem is required

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Usage

import { TaskNotFoundError, TaskAlreadyTerminalError } from '@frontmcp/sdk';

if (!task) {
  throw new TaskNotFoundError(taskId);
}

if (isTerminal(task.status)) {
  throw new TaskAlreadyTerminalError(task.status);
}