TL;DR: the code needs the standalone heaps package and it is not installed. Run `pip install heaps` and the import works.

## The error
```text
ImportError: No module named heaps
```

## Fix it
1. Install heaps:
   ```
   pip install heaps
   ```
   Expected: install completes.
2. Verify:
   ```
   python -c "import heaps; print('ok')"
   ```
   Expected: prints ok.

## When this applies
Use this when older graph/assembly tooling (ragout-era code, old networkx-adjacent scripts) raises the heaps error.

## When it does not apply
Modern networkx does not need heaps; if modern code raises this, something else is importing it. If the error names a different module, install that one instead.

## Compatibility
The heaps package on PyPI; needed by code written against the old pairing-heap API.

## Root cause
Years ago some graph tools imported pairing heaps from the standalone heaps package instead of implementing their own. Fresh environments built from incomplete requirements files miss it.

## Edge cases
heaps is pure python and installs anywhere. If the real problem is ancient code, consider whether upgrading the tool removes the dependency entirely.