Failed to initialize task manager: ${taskManagerResult.messa

Error message

Failed to initialize task manager: ${taskManagerResult.message}

What it means

workflow-builder calls AgentBuilderDefaults.manageTaskList to seed the task list before agent execution; if the returned result has success === false, this error is thrown embedding result.message. The task manager (backed by the agent's task tools / storage) could not be initialized, so the loop cannot track task completion and the run aborts.

Source

Thrown at packages/agent-builder/src/workflows/workflow-builder/workflow-builder.ts:299

      // Pre-populate taskManager with the planned tasks
      console.info('Pre-populating taskManager with planned tasks...');
      const taskManagerContext = {
        action: 'create' as const,
        tasks: tasks.map(task => ({
          id: task.id,
          content: task.content,
          status: 'pending' as const,
          priority: task.priority,
          dependencies: task.dependencies,
          notes: task.notes,
        })),
      };

      const taskManagerResult = await AgentBuilderDefaults.manageTaskList(taskManagerContext);
      console.info(`Task manager initialized with ${taskManagerResult.tasks.length} tasks`);

      if (!taskManagerResult.success) {
        throw new Error(`Failed to initialize task manager: ${taskManagerResult.message}`);
      }

      const executionAgent = new AgentBuilder({
        projectPath: currentProjectPath,
        model,
        tools: {
          'task-manager': restrictedTaskManager,
        },
        instructions: `${workflowBuilderPrompts.executionAgent.instructions({
          action,
          workflowName,
          tasksLength: tasks.length,
          currentProjectPath,
          discoveredWorkflows,
          projectStructure,
          research,
          tasks,
          resumeData,

View on GitHub (pinned to 75dd419e61)

Solutions

Read taskManagerResult.message in the thrown error for the underlying cause and fix that issue first
Verify the task-list tools are registered and storage/memory is correctly configured for the AgentBuilder run
Retry the workflow if the cause was a transient model/tool failure
If integrating custom defaults, ensure manageTaskList returns { success: true, tasks } on the happy path and only success:false for genuine failures

Defensive patterns

Strategy: try-catch

Validate before calling

export async function assertTaskListReady(manageTaskList: typeof AgentBuilderDefaults.manageTaskList, ctx: unknown) {
  const res = await manageTaskList(ctx);
  if (!res.success) throw new Error(`Task manager not ready: ${res.message}`);
  if (!Array.isArray(res.tasks)) throw new Error('Task manager returned no tasks array');
}
// probe before starting the full workflow

Type guard

export function taskManagerReady(r: { success: boolean; tasks?: unknown[] }): r is { success: true; tasks: unknown[] } {
  return r.success === true && Array.isArray(r.tasks);
}

Try / catch

try {
  const res = await AgentBuilderDefaults.manageTaskList(ctx);
  if (!res.success) throw new Error(`Task manager init failed: ${res.message}`);
} catch (e) {
  if (e instanceof Error && e.message.startsWith('Failed to initialize task manager:')) {
    // inspect res.message / storage & tool config, then retry
  }
  throw e;
}

Prevention

Verify task tools and their backing storage are configured before workflow runs
Smoke-test manageTaskList in a preflight step to catch misconfig early
Retry transient model/tool failures with bounded backoff
Keep res.message informative so the wrapped error is actionable

When it happens

Trigger: manageTaskList({ action: 'create'/seed ... }) returns { success: false, message } — e.g. the underlying agent call failed, the task tools are unavailable/misconfigured, storage for task state is unreachable, or the seeded task payload was rejected.

Common situations: Misconfigured task toolset or memory/storage in the AgentBuilder defaults, model/tool failures while creating tasks, or resource/permission errors writing task state in the target project.

Related errors

AI-assisted analysis of mastra-ai/mastra@75dd419e61 (2026-08-30). Data as JSON: /api/errors/987ba5cadf937675. Report an issue: GitHub.