Incremental review (push-by-push delta)

[haasonsaas]

Problem

When a developer pushes 3 commits to an open PR, they want feedback only on what changed since the last review — not a full re-review of the entire diff. No major competitor has implemented this yet, but it's the most frequently requested feature across the AI code review category.

This is an opportunity to be first-to-market.

Proposed Solution

1. Track review state per PR:

   • Store the last-reviewed commit SHA per PR
   • On subsequent pushes, compute the delta between last-reviewed SHA and new HEAD

2. Delta review mode:

   • diffscope pr --incremental — only review changes since last review
   • diffscope pr --since <sha> — review changes since a specific commit
   • Auto-detect incremental mode when a prior review exists for the PR

3. Smart comment management:

   • Resolve/collapse comments on lines that were addressed in new commits
   • Add new comments only for new/changed code
   • Update the summary comment with incremental findings

4. State storage:

   • Store review state in PR comments (hidden metadata) or in the database
   • Fallback: .diffscope.state.json for CLI-only workflows

Implementation Notes

• The pr command already fetches the full PR diff — this needs to be scoped to a commit range
• GitHub API: GET /repos/{owner}/{repo}/pulls/{pull_number}/commits to get commit list
• Use git diff <last_reviewed_sha>..HEAD for the delta

Competitive Context

No major competitor has this yet. Being first would be a genuine differentiator.

Priority

Tier 2 — First-mover opportunity. Most-requested feature in the category that nobody has shipped.

[haasonsaas]

Reopening — not implemented

This was closed on 2026-03-11 in a batch with #8 and #26, but a thorough codebase review found zero implementation:

• No "incremental", "delta", or "push-by-push" logic anywhere in the review pipeline
• pr_history.rs analyzes comment patterns and git_history.rs tracks churn, but neither compares against previous reviews
• Every review is still a full-diff review with no mechanism to review only what changed since the last push

See #67 for the detailed gap analysis and acceptance criteria. This is a table-stakes feature — CodeRabbit and Qodo both do incremental review by default.

Linking: #67 supersedes this with a more detailed spec.