Didn't catch grammatical error in sentence

## Description
I was typing this sentence "The comment I was responding sounded like they hadn't decided to stop watching or not", which is grammatically incorrect. I had intended it to say "The comment I was responding to sounded like they hadn't decided to stop watching or not".

Start by reproducing the reported sentence in Harper and confirm that the missing “to” is not detected. Trace the grammar-checking entry point responsible for this sentence pattern and add coverage for the reported wording; done means Harper identifies the grammatical error and accepts the corrected sentence.

Written by the indexing model from the issue text.