Chapter 1: Command Definition

Welcome to the Resume project! In this project, we are building a tool to help you pick up right where you left off in a conversation with an AI.

Before our tool can actually do anything, we need to introduce it to the system. This brings us to our first core concept: the Command Definition.

The Motivation: The Restaurant Menu

Imagine walking into a restaurant. Before you can eat, you need to look at a menu. The menu tells you:

1. The Name: "Spaghetti Carbonara"
2. The Description: "Pasta with eggs, cheese, and bacon."
3. The Shortcuts: "Item #42"

Crucially, the menu is just text. The chef doesn't start cooking the spaghetti the moment you walk in the door. They only start cooking (loading the heavy ingredients) when you actually order it.

In our Command Line Interface (CLI), the Command Definition is exactly like that menu item. It tells the terminal:

• "I exist."
• "My name is resume."
• "Here is what I do."
• "Don't load my heavy programming code until the user actually types my name."

Use Case: Letting the CLI Know We Exist

Our goal in this chapter is simple: We want to define a lightweight object that registers the resume command so users can see it when they ask for help, and run it when they are ready.

Step 1: Naming the Command

First, we define the basic identity. We tell the system that this command is named resume and give it a helpful description.

// --- File: index.ts ---
import type { Command } from '../../commands.js'

const resume: Command = {
  // The 'local-jsx' type means we will use a text-based UI later
  type: 'local-jsx', 
  name: 'resume',
  description: 'Resume a previous conversation',

What happens here:

• name: This is what the user types in the terminal (e.g., > my-tool resume).
• description: This text appears if the user types > my-tool --help.

Step 2: Aliases and Hints

Sometimes users prefer shortcuts, or they need to know what arguments to pass. We add aliases and hints to make the command friendlier.

  // Users can type 'continue' instead of 'resume'
  aliases: ['continue'],
  
  // Helps the user know they can pass an ID or text
  argumentHint: '[conversation id or search term]',

What happens here:

• aliases: If the user types continue, the system knows to run this resume command.
• argumentHint: This is a visual cue displayed in the terminal to show users they can provide extra details immediately.

Step 3: Lazy Loading (The "Kitchen" Logic)

This is the most important part for performance. We use a function to load the actual logic only when needed.

  // "Kitchen logic": Only import the heavy code when ordered
  load: () => import('./resume.js'),
}

export default resume

What happens here:

• load: This function uses a dynamic import. It points to ./resume.js.
• The code in ./resume.js contains the heavy logic for finding and restarting conversations. We don't read that file yet! We wait until the user presses Enter.

Under the Hood: How It Works

To visualize how the CLI uses this definition, let's look at what happens when the program starts.

1. Registration: The CLI starts up and reads your Command Definition (the menu).
2. Waiting: It waits for user input. It uses very little memory because the "heavy" code isn't loaded yet.
3. Activation: The user types resume.
4. Loading: The CLI sees a match, calls your load() function, and finally grabs the real code.

Here is the sequence of events:

Deep Dive: The load Property

Let's look closer at that last piece of code, as it connects this chapter to the rest of the application.

  load: () => import('./resume.js'),

This single line connects the Command Definition (Chapter 1) to the Command Execution Flow (Chapter 2).

• Before this runs: The CLI only knows about the command.
• After this runs: The CLI has access to the run function exported by resume.js.

By separating the Definition (metadata) from the Implementation (logic), our CLI starts up instantly, no matter how complex the resume feature becomes.

Summary

In this chapter, we created the "Menu Item" for our command. We learned:

1. How to define the identity (name and description) of the command.
2. How to add usability features like aliases and argument hints.
3. How to use lazy loading so our code is efficient and fast.

Now that our command is defined and registered, the CLI knows what to call. But what happens inside that imported file when the command actually runs?

Let's find out in the next chapter: Command Execution Flow.

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