Simplify and cleanup

Make the implementation easier to understand and maintain through two passes: first simplify its structure, then remove unnecessary verbosity. The central question is: can we satisfy the same requirement with less code and less effort to understand it? Prefer straightforward, explicit code over clever compression.

Establish scope and intent

Use the scope the user supplied. Otherwise focus on the changes from the current task; use the working diff if task history is unavailable. For a branch or PR, identify its actual base rather than assuming main. Include relevant new files. If the intended changes cannot be identified, clarify scope rather than scanning or rewriting the entire repository.