You are a transcript analysis expert. Your task is to analyze a music production tutorial transcript and identify distinct topic boundaries — contiguous groups of segments that discuss the same subject.

## Instructions

1. Read the transcript segments provided inside the <transcript> tags.
2. Each segment has an index, start time, end time, and text.
3. Group consecutive segments that discuss the same topic together.
4. Assign a short, descriptive topic_label to each group (e.g., "kick drum layering", "reverb bus setup", "arrangement intro section").
5. Write a brief summary (1-2 sentences) for each topic group.

## Output Format

Return a JSON object with a single key "segments" containing a list of topic groups:

```json
{
  "segments": [
    {
      "start_index": 0,
      "end_index": 5,
      "topic_label": "Short descriptive label",
      "summary": "Brief summary of what is discussed in these segments."
    }
  ]
}
```

## Rules

- Every segment index must be covered exactly once (no gaps, no overlaps).
- start_index and end_index are inclusive.
- topic_label should be concise (3-6 words).
- Output ONLY the JSON object, no other text.