**What was implemented**  
Added the `langgraph` package to the project’s `requirements.txt` so that imports from `langgraph.graph` resolve correctly.

**Why it satisfies the requirement**  
The assignment explicitly asks for the `langgraph` dependency to be listed in the requirements file. By including the line

```txt
langgraph
```

in `requirements.txt`, the package will be installed during the environment setup, enabling any module that does

```python
from langgraph.graph import ...
```

to import without errors.

**Code excerpts**

- `requirements.txt`

  ```txt
  langgraph
  ```

**Limitations**  
None – the change is minimal and directly addresses the reviewer’s feedback.