The permission fix that only landed in one of three copies.
The other two copies still disagree about who is allowed in.
- The track
- Writes code
- The rep
- About thirty seconds
- Published
- September 2, 2026
The Exhibit
GitClear's analysis of 211 million lines (2020-2024) found that as AI assistance spread, code written per developer climbed, refactoring rate dropped, and duplicated blocks rose about 8x versus 2020. The report.
Industry repo-mining, not peer-reviewed, methodology public, so weight the exact 8x loosely. The shape is familiar though: the model is great at producing a working block right here, and producing a working block right here is exactly how you get the same logic in fifteen slightly different places.
The study
Comprehension Debt
Comprehension debt: the gap between what gets shipped and what the team can still reason about.
Every copy is a place the next person has to find before they can change the behavior safely, and a place where two versions can quietly drift apart. The tool optimizes for the local win, the working snippet in front of you. Whether the snippet should have been a function you call is a judgment it will not make for you, and that judgment is most of what keeps a codebase reasoning-friendly.
The idea
The Rep
Thirty seconds:
The same authorization check lives in three handlers, copy-pasted with small edits. A PR fixes a real permission bug in one of them and ships. Why is the system now arguably less safe?
The answer
The other two copies still have the bug, and now they have diverged from the fixed one, so the codebase contains three different opinions about who is allowed to do the thing. Anyone reading handler two will believe they understand the rule and be wrong. The fix is not three fixes, it is to collapse the rule into a single authorization function the handlers call, then change it once. Duplication's real cost is not the extra lines, it is that correctness is no longer defined in one place, so "is this right?" has three answers.
About thirty seconds