Numerous grammar issues?

**The Error**
I've just started trying out Harper by typing my handwritten notes into VS Code, which I'm sure are riddled with basic grammar mistakes. Harper, however, didn't flag a single error in my notes, which made me suspicious. So I deliberately used these sentences to test Harper, and it failed to find any mistakes – both in VS Code **and** on the Harper website. Am I misunderstanding Harper's intended use case?

**Examples (2-3):**
1. Their going two the store accept for John, who forgot his coat on the chair who was broken.
2. The committee have reached its decision, but neither the chairperson nor the members was willing to explain it.
3. I believe this to be very basic grammar mistakes.

**References**
Any grammar rules or resources that support this.
I believe these to be very basic grammar mistakes.

**Potential Edge Cases**
When might this not apply?
I'm not qualified to determine this.

Reproduce the three example sentences in VS Code and on the Harper website, then determine whether the behavior is an implementation gap or an intended limitation. Read the project's grammar-checking guidance and existing issue discussion before identifying the relevant rule coverage. Done means the examples are either correctly flagged with regression coverage or the intended behavior is clearly documented.

Written by the indexing model from the issue text.