golem-add-agent-moonbit

Agent Building

Adding a new MoonBit agent to a Golem component. Use when the user asks to create, add, or define a new agent type in a MoonBit Golem project.

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Prompt to paste

I want to install this Agent Skill for this project in Codex.

Source SKILL.md: https://github.com/golemcloud/golem/blob/HEAD/golem-skills/skills/moonbit/golem-add-agent-moonbit/SKILL.md

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First, summarize what it does, its dependencies, license status if identifiable, and any risks. Show the exact files you propose to add under .agents/skills/golem-add-agent-moonbit/. Do not write files or run scripts until I approve.

After I approve, install the complete skill folder, including required referenced files, into that project location. Verify it is discoverable, then tell me its actual invocation name and how to use it. Do not claim it is installed until you have verified it.

Copying this prompt does not install or run the skill. Review third-party files before use. Codex skill guide

Adding a New Agent to a MoonBit Golem Component

Overview

An agent is a durable, stateful unit of computation in Golem. Each agent type is defined as a struct annotated with #derive.agent and has a constructor fn AgentName::new(...) plus public methods pub fn AgentName::method(self: Self).

Steps

Create the agent file — add a new file src/<agent_name>.mbt
Define the agent struct — annotate with #derive.agent
Add constructor — fn AgentName::new(param: Type) -> AgentName
Add methods — pub fn AgentName::method(self: Self) -> ReturnType
Build — run golem build to verify

Agent Definition

#derive.agent
struct MyAgent {
  name: String
  mut count: UInt
}

fn MyAgent::new(name: String) -> MyAgent {
  { name, count: 0 }
}

pub fn MyAgent::get_count(self: Self) -> UInt {
  self.count
}

pub fn MyAgent::increment(self: Self) -> UInt {
  self.count = self.count + 1
  self.count
}

Custom Types

All parameter and return types must have schema support. For custom structs and enums, annotate with #derive.golem_schema:

#derive.golem_schema
struct MyData {
  field1: String
  field2: UInt
}

#derive.golem_schema
enum Status {
  Active
  Inactive(String)
}

Returning Failures

Agent methods should distinguish between domain errors (expected failure outcomes) and uncaught errors:

Uncaught errors (uncaught raise, aborts, runtime panics) are not returned to the caller as a failed invocation. Golem treats them as crashes: the invocation is retried according to the agent's retry policy, and if the retries are exhausted the agent itself becomes failed.
Domain errors that the caller should observe as a normal failure result must be expressed in the method's return type using Result[T, E]. Custom error types need #derive.golem_schema.

#derive.golem_schema
pub(all) enum WithdrawError {
  InsufficientFunds(UInt64)
  AccountClosed
}

#derive.agent
struct Wallet {
  owner : String
  mut balance : UInt64
  mut closed : Bool
}

fn Wallet::new(owner : String) -> Wallet {
  { owner, balance: 0, closed: false }
}

pub fn Wallet::withdraw(self : Self, amount : UInt64) -> Result[UInt64, WithdrawError] {
  if self.closed {
    Err(AccountClosed)
  } else if amount > self.balance {
    Err(InsufficientFunds(self.balance))
  } else {
    self.balance = self.balance - amount
    Ok(self.balance)
  }
}

Returning Err(...) completes the invocation successfully — the caller receives the error as a value. Letting an exception propagate out of the method (e.g. an unhandled raise, or abort(...)) will instead trigger a retry and eventually fail the whole agent.

Key Constraints

Constructor parameters form the agent identity — two agents with the same parameters are the same agent
Agents are created implicitly on first invocation — no separate creation step
Invocations are processed sequentially in a single thread — no concurrency within a single agent
Method names use snake_case
Never edit generated files — golem_reexports.mbt, golem_agents.mbt, and golem_derive.mbt are auto-generated by golem build
Only pub fn methods are exposed as agent methods — private functions are not exported