[Feature Request] Include actual context window usage in statusline JSON

Problem

The context_window field in statusline JSON does not reflect the actual context window usage shown by /context command.

Current behavior

Statusline JSON provides:

"context_window": {
  "total_input_tokens": 4042,
  "total_output_tokens": 9412,
  "context_window_size": 200000
}

Total: ~13K tokens

Expected behavior

/context command shows actual usage: 172K/200K (86%)

Breakdown:

• System prompt: 3.3K
• System tools: 15.7K
• MCP tools: 18.2K
• Memory files: 0.4K
• Messages: 89.5K
• Autocompact buffer: 45K

Request

Please include the actual context window occupancy in the statusline JSON, similar to what /context displays. This would allow custom statusline scripts to show accurate context usage.

Suggested addition:

"context_window": {
  "used_tokens": 172000,
  "context_window_size": 200000,
  "percent_used": 86
}

Environment

• Claude Code version: 2.0.69
• Model: claude-opus-4-5-20251101