[FEATURE] Add active agents/tasks to statusLine JSON input

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When using a custom statusLine command, it would be valuable to see information about currently running background agents or tasks.

Use Case:

When working on complex projects, I often have background agents running (via the Task tool with run_in_background: true). Currently, there's no way to see this information in the status line - I have to use /tasks to check on them.

Being able to display active agents in the status line would provide:

• At-a-glance visibility into what's running in the background
• Awareness of when agents complete without interrupting workflow
• Better context when multiple parallel tasks are in progress

Proposed Solution

Add an active_tasks or background_agents field to the statusLine JSON input:

{
"active_tasks": [
{
"id": "abc123",
"description": "Running tests",
"status": "running",
"agent_type": "build-validator"
}
],
// ...
}

Alternative Solutions

Current Workaround:

None - this information isn't accessible to statusLine commands.

Priority

Medium - Would be very helpful

Feature Category

Interactive mode (TUI)

Use Case Example

_No response_

Additional Context

_No response_