docs: add llm.md for react counter

Author: topheman

demo/counter-react/js/llm.md

@@ -0,0 +1,175 @@
+# Building a Counter with @webrtc-remote-control/react
+
+## Application Behavior
+This application creates a real-time counter that can be controlled remotely:
+
+1. **Master Device (e.g., Laptop)**
+   - Displays a QR code on the screen
+   - Shows the current counter value
+   - Updates in real-time when remote devices interact
+   - Can display multiple connected remote devices and their counter values
+
+2. **Remote Device (e.g., Smartphone)**
+   - User scans the QR code from the master device
+   - Opens a simple interface with + and - buttons
+   - Each button press instantly updates the counter on the master device
+   - Connection status is clearly displayed
+
+The library does handle all the WebRTC communication automatically, making the counter update in real-time across devices. It also handles any reload of the page, and will reconnect to the same peer if the page is reloaded.
+
+## Application Structure
+```
+Root
+└── WebRTCRemoteControlProvider
+    ├── Master (displays QR code & counter)
+    └── Remote (shows + and - buttons)
+```
+
+## Prerequisites
+The library is a wrapper for [PeerJS](https://peerjs.com/), you will need to include the PeerJS library in your project.
+
+## Mode Configuration
+You should determine the mode based on the URL:
+- `mode="master"`: When accessing the page directly
+- `mode="remote"`: When the URL contains a hash (peer ID)
+
+For example:
+- `https://your-app.com` → Set `mode="master"`
+- `https://your-app.com#abc123` → Set `mode="remote"`
+
+## Getting Started
+The library does automatically handle WebRTC connections, but you should:
+1. Wrap your application with `WebRTCRemoteControlProvider`
+2. Implement Master and Remote components
+3. Use the `usePeer` hook for WebRTC communication
+
+## Implementation Guide
+
+### 1. Root Component Setup
+You should initialize the WebRTC context like this:
+```jsx
+<WebRTCRemoteControlProvider
+  mode={mode}
+  init={({ getPeerId }) => new Peer(getPeerId(), getPeerjsConfig())}
+  masterPeerId={window.location.hash?.replace("#", "") || null}
+  sessionStorageKey="webrtc-remote-control-peer-id-react"
+>
+```
+
+### 2. Master Component Implementation
+The library does provide:
+- WebRTC connection management
+- Peer discovery and connection
+- Real-time data transmission
+- Connection state handling
+- QR code generation for peer ID
+
+You should implement:
+- Counter state management (increment/decrement logic)
+- Display of current counter value
+- List of connected remotes and their individual counters
+- UI for the master view
+- Error handling specific to counter operations
+
+Here's a minimal Master component:
+```jsx
+function Master() {
+  const { ready, api, peer } = usePeer();
+  const [remotesList, setRemotesList] = useState([]);
+
+  useEffect(() => {
+    if (ready) {
+      // Handle remote connections
+      api.on("remote.connect", ({ id }) => {
+        setRemotesList(prev => [...prev, { id, counter: 0 }]);
+      });
+
+      // Handle remote disconnections
+      api.on("remote.disconnect", ({ id }) => {
+        setRemotesList(prev => prev.filter(remote => remote.id !== id));
+      });
+
+      // Handle incoming counter commands
+      api.on("data", ({ id }, data) => {
+        if (data.type === "COUNTER_INCREMENT") {
+          setRemotesList(prev =>
+            prev.map(remote =>
+              remote.id === id
+                ? { ...remote, counter: remote.counter + 1 }
+                : remote
+            )
+          );
+        }
+      });
+    }
+  }, [ready]);
+
+  return (
+    <div>
+      <h1>Master Counter</h1>
+      {peer?.id && <QRCode value={peer.id} />}
+
+      <h2>Connected Remotes ({remotesList.length})</h2>
+      <ul>
+        {remotesList.map(remote => (
+          <li key={remote.id}>
+            Remote {remote.id}: {remote.counter}
+          </li>
+        ))}
+      </ul>
+
+      <h2>Total: {remotesList.reduce((sum, remote) => sum + remote.counter, 0)}</h2>
+    </div>
+  );
+}
+```
+
+### 3. Remote Component Implementation
+The library does provide:
+- WebRTC connection to master
+- Real-time data transmission
+- Connection state management
+- Automatic reconnection handling
+
+You should implement:
+- UI with + and - buttons
+- Counter command sending logic
+- Remote device identification
+- Connection status display
+- Error handling specific to counter operations
+
+Here's a minimal Remote component:
+```jsx
+function Remote() {
+  const { ready, api } = usePeer();
+
+  const increment = () => {
+    if (ready) {
+      api.send({ type: "COUNTER_INCREMENT" });
+    }
+  };
+
+  return (
+    <div>
+      <h1>Remote Control</h1>
+      <button onClick={increment}>+</button>
+    </div>
+  );
+}
+```
+
+## Best Practices
+You should:
+- Use the `usePeer` hook for all WebRTC operations
+- Implement proper error handling, using the `humanizeError` function
+- Clean up connections in useEffect
+- Make sure your application correctly behaves in reconnection scenarios
+
+## Technical Requirements
+The library does:
+- Handle WebRTC signaling through PeerJS
+- Manage real-time bidirectional communication
+- Maintain persistent connections
+- Handles connection errors
+- Handles reconnection scenarios
+- Provide React hooks for state management