Support custom status line and context-window usage in the Copilot desktop app

Summary

The native GitHub Copilot desktop app does not render the custom status line or context-window footer configured in ~/.copilot/settings.json, even though the same configuration works in the terminal-hosted Copilot CLI.

Environment

• OS: Windows
• GitHub Copilot desktop app: 1.1.19
• Desktop executable: C:\Users\<user>\AppData\Local\Programs\GitHub Copilot\github.exe
• GitHub Copilot CLI: 1.0.84-4

Configuration

{
  "statusLine": {
    "type": "command",
    "command": "powershell.exe -NoProfile -ExecutionPolicy Bypass -File \"C:\\Users\\<user>\\.copilot\\statusline.ps1\""
  },
  "footer": {
    "showContextWindow": true,
    "showCustom": true
  }
}

The configured PowerShell command reads the status payload from stdin and prints context-token usage.

Steps to reproduce

1. Configure statusLine.command, footer.showCustom, and footer.showContextWindow in ~/.copilot/settings.json.
2. Start Copilot CLI from PowerShell by running copilot.
3. Send a prompt and observe that the custom context usage (for example, 49.5k/? tokens) appears in the terminal footer.
4. Close the terminal session and launch the native desktop app using github.exe.
5. Open a session and send a prompt.

Actual behavior

The desktop app does not display the custom status-line output or a context-window usage indicator. The command itself is valid and works in the terminal CLI.

Expected behavior

The desktop app should either:

1. honor statusLine.command and the relevant footer.* settings, or
2. provide a native equivalent that continuously shows used/remaining context-window capacity for the active session.

Why this matters

Context-window visibility helps users decide when to summarize, checkpoint, or start a new session before earlier context is compacted or lost. Users moving between the terminal CLI and native desktop app should have equivalent visibility into session context usage.

Comienza comparando el comportamiento de la aplicación de escritorio iniciada mediante github.exe con el comportamiento de Copilot CLI en el terminal para ~/.copilot/settings.json. Sigue cómo se gestionan statusLine.command, footer.showCustom y footer.showContextWindow, y verifica después si la sesión de escritorio renderiza la salida configurada o muestra continuamente el uso de la ventana de contexto, como la CLI.