Ruff defaults turn linting into agent drift

Astral released Ruff v0.16.0 with 413 rules enabled by default, up from 59, and Simon Willison traced unpinned Ruff installs to fresh CI failures across several Python projects. Why it matters: Coding agents treat green checks as a receipt. When a tool changes its default rule set under them, the agent may spend a run fixing surprise lint instead of the task you assigned.

Try this: Pin Ruff where CI must stay stable, or run the new default check once and commit the rule choice before handing the repo to an agent.