```python
# /// intent
# goal   = "Add the line '- release notes' after the line '- changelog' in notes.md, failing if '- changelog' does not occur exactly once"
# reads  = ["notes.md"]
# writes = ["notes.md"]
# output = "none"
# ///

import json
from pathlib import Path

# Read the file content
path = Path("notes.md")
content = path.read_text()

# Split the content into lines
lines = content.splitlines()

# Find the index of '- changelog'
changelog_index = -1
found_count = 0
for i, line in enumerate(lines):
    if line.strip() == "- changelog":
        found_count += 1
        changelog_index = i

# Check if exactly one occurrence
if found_count != 1:
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