Diff suggestion comments duplicated instead of moving with code

[sentry-junior]

Diff suggestion comments are sometimes misplaced — duplicated in their original position rather than moving with the associated code when a PR diff shifts.

Symptom

When warden posts a diff suggestion on a PR, if the surrounding code moves (e.g. a block is relocated in a later commit), the suggestion comment is duplicated at the original line instead of following the code it was attached to.

Known facts

• Observed on active PRs where diff suggestions were generated by warden.
• The duplicate appears at the original line position; the moved code does not get the suggestion carried over.

Unknowns

• Whether this is a GitHub API limitation (suggestions are line-anchored, not semantically anchored) or a warden-side issue in how suggestions are constructed.
• Frequency / reproducibility across different PR shapes.

Root-cause hypotheses

• GitHub line-anchoring (high confidence): GitHub's suggestion API anchors comments to a specific line number in the diff. When code moves, the anchor becomes stale and GitHub may render a duplicate or orphaned comment. Warden may not have logic to detect or suppress this.
• Warden re-posts suggestions on diff refresh (medium confidence): If warden re-evaluates the PR after a new commit and re-posts suggestions without deduplication, it would produce duplicate comments.

Next steps

• Audit warden's suggestion posting logic for deduplication guards.
• Confirm whether GitHub's native suggestion API has any semantic-anchor support or if this is inherently positional.