GA highlights disappear after teacher edits category scores

# GA highlights disappear after teacher edits category scores

When a teacher manually adjusts the category scores on a GA-graded paper (e.g., to lower an inflated score for an incomplete essay), the on-doc highlights disappear.

## Reproduction

1. As a teacher, run GA on a submission.
2. Manually edit one or more category scores in the grading panel.
3. Observe that the inline highlights on the document are gone.

Specifically reported on a paper where the student didn't finish — teacher wanted to lower the score and adjusted categories, then noticed no highlights remained on the doc.

## Expected

Highlights are tied to the GA's textual feedback (what spans got flagged for what reason) and should persist even when numeric category scores are edited. The teacher is changing the score, not the analysis.

## Actual

Highlights vanish after a category edit. The student loses the actionable inline feedback they would have used to revise.

## Impact

Defeats the value of letting teachers adjust scores. Teachers need to override the GA's number without nuking the underlying analysis. Reported 2026-03-02.

## Affected versions

Reported 2026-03-02.

## Suspected cause

Highlight rendering is gated on "GA result hasn't been edited" rather than just "GA result exists." Edit invalidates the cached GA payload. Decouple highlights from category-score state.

## Workaround

None — once the highlights are gone, the only way to get them back is to re-run GA, which re-grades the paper.