Codex stress tests on old repos reveal a new idea: an agent for the margins

joonasvirtanen · x · 2026-07-23

After stress-testing Codex on legacy repositories, the interesting part wasn’t what it generated — it was what it noticed: dead code, missing tests, and undocumented assumptions.

The author compares those marginal notes to medieval “glosses” and argues for giving the margins their own agent, so the system can actively surface cleanup and documentation work instead of only writing code.

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