fix(pr-review): judge earlier findings per head, rebase-safe follow-up delta

[Makisuo]

Follow-up to #1001, #1014 and #1016, rebased onto main. The kickoff's changed-files line keeps the exact shape followUpScope (#1014) parses, so the coverage gate reads a rebase-safe delta the same way.

Earlier findings

The mechanical repeat filter dropped any new finding with the same path and category within three lines of an open or dismissed one, which suppressed a new bug sitting next to an old one and missed an old issue whose code moved.

• withoutRepeats now drops only near-exact restatements: same path, category, a line within 3, and titles sharing at least 60% of their words.
• The follow-up kickoff and PR_REVIEW_SYSTEM_PROMPT ask the reviewer to judge each open finding at the new head: follow moved code, modified lines are not a fix, leave it open when unsure, never re-file an open finding, but do file a different defect nearby.

Follow-up delta across a rebase

fetchChangedPaths(previousSha, headSha) was a three-dot compare, so after a force-push rebase it listed every file the base branch changed.

• VcsProviderClient.fetchChangesSince returns { paths, rewritten }.
• GitHub: when the compare status is ahead/identical the forward diff is used as before. Otherwise each head is compared against the PR base and only files whose own change differs are kept (vcs/range-diff.ts, hunk-header line numbers ignored; binary/oversized files, added and dropped files count as changed).
• No base sha, or a comparison at GitHub's 300-file cap, yields paths: undefined and the kickoff asks for a full review (previously a >300-file compare was truncated silently).

Tests

range-diff.test.ts, new findings.test.ts cases (new bug beside an old one kept, moved code left to the model, kickoff wording), and GithubProvider.pulls.test.ts cases for the ancestor path, a rebase that excludes base-branch files, and both fallbacks. bun run test for pr-review and the GitHub vendor: backend 112 and apps/ai chat 185 passing.

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Summary by CodeRabbit

• Bug Fixes
  • Follow-up reviews now account for rebases and force-pushes, focusing on files whose changes differ and requesting a full review when the comparison is unavailable.
  • Open findings are checked against the current code, including when code has moved. Restated findings stay open rather than being filed again, while distinct nearby defects can still be reported.
  • Follow-up review summaries show the review scope and indicate when branch history was rewritten.

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Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: d16f55cd-3086-4669-9c8d-9783a6c50341

📥 Commits

Reviewing files that changed from the base of the PR and between fe61113 and 3e1bb74.

📒 Files selected for processing (13)

• apps/ai/src/chat/prompts.ts
• apps/ai/src/chat/review-coverage.test.ts
• packages/backend/src/services/integrations/vcs/VcsProviderClient.ts
• packages/backend/src/services/integrations/vcs/range-diff.test.ts
• packages/backend/src/services/integrations/vcs/range-diff.ts
• packages/backend/src/services/integrations/vcs/vendor/github/GithubAppClient.ts
• packages/backend/src/services/integrations/vcs/vendor/github/GithubProvider.ts
• packages/backend/src/services/integrations/vcs/vendor/github/__tests__/GithubProvider.pulls.test.ts
• packages/backend/src/services/pr-review/PrReviewConversationService.test.ts
• packages/backend/src/services/pr-review/PrReviewService.test.ts
• packages/backend/src/services/pr-review/PrReviewService.ts
• packages/backend/src/services/pr-review/findings.test.ts
• packages/backend/src/services/pr-review/findings.ts

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