Include subagent/task info in status line data

Feature Request

When using the Task tool to spawn subagents, there's no way to monitor their status from the status line. The JSON data passed to the status line script has no fields for running subagents.

Requested Data

Include subagent/task information in the status line JSON, e.g.:

{
  "subagents": [
    {
      "id": "abc123",
      "type": "Explore",
      "status": "running",
      "description": "Research multi-line status bar"
    }
  ]
}

Desired Behavior

With this data available, users could render a second status line row showing active subagents in the same style as their main status bar. Multi-line status bars are already supported (multiple print() calls), so the only missing piece is the data.

Example output:

~/project - main ~ Opus 4.6 | [███████████░░░░] 55% | ↓ 12k | ↑ 8k | 20k/200k
  ⚙ Subagents: [Explore] "Research codebase" | [Bash] "Run tests"

Consumption Example

With the requested data, adding subagent visibility to an existing status line script would be straightforward:

subagents = data.get("subagents") or []
if subagents:
    running = [s for s in subagents if s.get("status") == "running"]
    if running:
        parts = [f"[{s['type']}] \"{s['description']}\"" for s in running]
        print(f"  ⚙ Subagents: {' | '.join(parts)}")

This would give visibility into what's happening when multiple agents are working in parallel, directly in the status bar.