JuliusBrussee/caveman · error

cave_delegate_missing_task

Error message

cave_delegate_missing_task

What it means

The caveman-delegate MCP server throws this when a tools/call arrives without a usable arguments.task — the task must be a non-empty string; it is the one required argument of the delegate tool and the prompt handed to the worker subprocess.

Source

Thrown at agents/delegate/caveman-delegate-mcp.mjs:143

  },
};

async function handle(msg) {
  const { id, method, params } = msg;
  if (method === "initialize") {
    return {
      protocolVersion: params?.protocolVersion || PROTOCOL_FALLBACK,
      capabilities: { tools: { listChanged: false } },
      serverInfo: { name: "caveman-delegate", version: "0.1.0" },
    };
  }
  if (method === "tools/list") return { tools: [TOOL] };
  if (method === "ping") return {};
  if (method === "tools/call") {
    if (params?.name !== TOOL.name) throw new Error(`unknown tool: ${params?.name}`);
    if (process.env.CAVEMAN_DELEGATE_CHILD === "1") throw new Error("cave_delegate_depth_exceeded");
    const task = params?.arguments?.task;
    if (!task || typeof task !== "string") throw new Error("cave_delegate_missing_task");
    const r = await runWorker(task, params?.arguments?.cwd);
    const lines = [r.out || "(worker produced no output)"];
    if (r.usage) {
      const u = r.usage;
      let usageLine = `delegate usage (measured, provider-reported): input ${u.input + u.cacheRead + u.cacheWrite} (cacheRead ${u.cacheRead}, cacheWrite ${u.cacheWrite}), output ${u.output}`;
      if (u.cost > 0) usageLine += `, cost $${u.cost.toFixed(4)}`;
      lines.push("---", usageLine);
    }
    if (r.code !== 0) {
      lines.push("---", `worker exit ${r.code}: ${r.err.slice(-500)}`);
      return { content: [{ type: "text", text: lines.join("\n") }], isError: true };
    }
    return { content: [{ type: "text", text: lines.join("\n") }] };
  }
  if (method?.startsWith("notifications/")) return undefined;
  throw Object.assign(new Error(`method not found: ${method}`), { code: -32601 });
}

View on GitHub (pinned to 27d5a3981a)

Solutions

1. Pass arguments as { task: "<non-empty instruction string>" }
2. Validate and require the task field in the caller's form or schema before issuing tools/call
3. If the task is built from variables, fail loudly upstream when it composes to empty

Example fix

// before
await rpc("tools/call", { name, arguments: { cwd } }); // task missing

// after
if (!task?.trim()) throw new Error("task is required");
await rpc("tools/call", { name, arguments: { task, cwd } });

const callArgs = { task, cwd };
if (typeof callArgs.task !== "string" || callArgs.task.trim() === "") {
  throw new Error("delegate requires a non-empty task string");
}
await rpc("tools/call", { name, arguments: callArgs });

function isDelegateArgs(a) {
  return typeof a === "object" && a !== null && typeof a.task === "string" && a.task !== "";
}

try { await callDelegate(task); }
catch (e) {
  if (String(e?.message) === "cave_delegate_missing_task") { /* surface a form-level 'task required' error */ }
  else throw e;
}

When it happens

Trigger: Calling the delegate tool with arguments omitted, with task set to null/undefined/number/object, or with an empty string — commonly a client schema bug or a template variable that rendered empty.

Common situations: Client forms that submit before input; templating producing empty strings; passing the task under a different key (prompt, query, description); JSON.stringify dropping undefined fields.

Related errors

• ${key} is required
• filters must be an object
• unknown trace filter(s): ${unknown.sort().join(", ")}
• filter ${key} must be a non-empty array of non-empty strings
• filter status_class values must be 2xx, 4xx, or 5xx

AI-assisted analysis of JuliusBrussee/caveman@27d5a3981a (2026-08-15). Data as JSON: /api/errors/e5d4448018267bc2. Report an issue: GitHub.