Migration Diary: Rebuild the Diff Budget Before You Leave a Paid Coding Agent

Description and use

Implementing a numeric diff budget enables a safe transition away from paid AI agents by limiting patch size and preventing uncontrolled code changes.

Problem

After canceling a paid coding agent, teams risk accepting large, opaque patches that can silently modify many files, leading to uncontrolled changes and difficult reviews.

Outcome

Teams can safely transition away from paid AI agents by enforcing numeric diff budgets, preventing large, uncontrolled patches and maintaining code quality.

Workflow

• 1. Export all leftover paid diffs to a local directory.
• 2. Count files and lines in the working tree with git diff --numstat.
• 3. Parse each unified diff with a custom Python scorer to tally files, hunks, added and deleted lines.
• 4. Compare counts against the .diff-budget.json limits.
• 5. Reject any patch that exceeds the budget; otherwise apply it.
• 6. Commit the .diff-budget.json to the repo so all teammates share the same constraints.

Evidence

A budget is not a linter, and it is not a model quality score either. It is a hard ceiling on how much tree mutation one agent turn may propose.

Source

Store the budget beside the repository, not inside a vendor dashboard you are about to abandon.

Source