Generate Pull Request Description

Generate a short, narrative PR description that tells reviewers why this change exists and what to expect when they open the diff. Reviewers skim. If the description is long, they skip it. Respect their time.

Modes

Parse $ARGUMENTS. --split selects an alternate workflow. The post-draft quality step (Step 6.5) runs the full review + simplify loop by default; the --no-* / --quick flags below scale it down. All flags compose with the default and split workflows.