/describe

Generate a commit description for the current session's jj change

# jj-describe

Generate a commit description for a Claude session's jj change

## instructions

You must follow these steps to create a proper commit message:

1. **Determine session ID:**
   - Use the session ID from the system reminder (current session)
   - Store the session ID for use in subsequent steps

2. **Check if a change exists for the session:**
   - Run: `jjagent change-id <session-id>` to check if a change exists
   - **IMPORTANT:** If the command fails or returns an error, immediately stop and inform the user:
     "No jj change exists for this session yet. There's nothing to...