[Bug] Subagent status line JSON missing effort field for non-custom subagents

Bug Description
the subagent status line JSON contains no info about "normal" subagent's effort. effort is only non-empty for "proper" custom subagents that have an effort defined in their agent MD file. It is not clear with which effort subagents are working.

Environment Info

• Platform: linux
• Terminal: konsole
• Version: 2.1.238
• Feedback ID: 2622e644-32d2-4652-b3ed-dfd49d9af588

Output as of 2.1.238:

{
  "session_id": "...",
  "transcript_path": "...",
  "cwd": "...",
  "prompt_id": "...",
  "columns": 169,
  "tasks": [
    {
      "id": "a9694f99227974bfe",
      "type": "local_agent",
      "status": "running",
      "description": "haiku (low) - Infinite block test 1",
      "label": "Backgrounding infinite bash processes",
      "startTime": 1787309508060,
      "model": "claude-haiku-4-5-20251001",
      "contextWindowSize": 200000,
      "tokenCount": 21626,
      "tokenSamples": [
        ...
      ],
      "cwd": "...."
    },
[...]
    {
      "id": "aeee17882615c47fe",
      "type": "local_agent",
      "status": "running",
      "description": "haiku (low) - Infinite block test (nested)",
      "label": "Reinvoking timeout sleep loop",
      "startTime": 1787309763895,
      "model": "claude-haiku-4-5-20251001",
      "contextWindowSize": 200000,
      "tokenCount": 19584,
      "tokenSamples": [
        ...
      ],
      "cwd": "..."
    },
  [...]
  ]
}

As you can see, the "effort" field is simply not present.

Looks like this:

<img width="1466" height="103" alt="Image" src="https://github.com/user-attachments/assets/8436006c-ba60-4bff-9ddc-74f85a69dc76" />

The "haiku (low)" was only generated due to an instruction in CLAUDE.md to include the effort in the model description - however that is probably hallucinated.

When you spawn a custom subagent:

---
name: test-foobar
description: a test agent
model: sonnet
effort: xhigh
---

You are a test agent used during status line development. You just block indefinitely.

it looks like this:

{
  "session_id": "...",
  "transcript_path": "...",
  "prompt_id": "...",
  "columns": 169,
  "tasks": [
    {
      "id": "a30b0dd85fa8869f6",
      "type": "local_agent",
      "status": "completed",
      "description": "test-foobar - Launch test",
      "label": "test-foobar - Launch test",
      "startTime": 1787310665568,
      "model": "claude-sonnet-5",
      "effort": "xhigh",
      "contextWindowSize": 1000000,
      "tokenCount": 20949,
      "tokenSamples": [
        [...]
      ],
      "cwd": "..."
    }
  ]
}