fix(server): detect file renames in review diffs

[jakeleventhal]

Supersedes #3916 with a smaller implementation rebased onto the current UI and server architecture.

Problem

A filesystem rename appears as an unrelated deletion and addition in the Working tree review because tracked and untracked patches are generated separately.

Fix

• Generate one unified working-tree patch when untracked files are present by copying the real Git index to a scoped temporary index.
• Add untracked paths as intent-to-add only in that temporary index, then run git diff --find-renames once across tracked and untracked changes.
• Preserve staged deletions and fall back to the existing separate-diff path if temporary-index setup fails.

The temporary index is necessary because Git cannot correlate a tracked deletion with an untracked destination unless both paths participate in the same diff. The user's real index is never modified, and the temporary file is removed when the scoped operation finishes.

Before

The current UI renders an exact filesystem rename as a deletion plus an addition:

After

The same fixture renders as one rename:

Rename with a minor edit

Rename detection is preserved when the destination also changes—in this fixture, one line is edited after the file is moved:

Performance

The normal path with no untracked files still uses two Git processes. When untracked files exist, the previous implementation used N + 2 processes (one diff --no-index per untracked file); this implementation uses a fixed five, with the independent staged-deletion and index-path lookups run concurrently. That is two extra processes for one untracked file, equal at three, and fewer for four or more.

On a tiny exact-rename fixture over 100 measured runs after 10 warmups, the one-file worst case increased from 16.6 ms median / 19.7 ms p95 to 33.9 ms median / 38.4 ms p95. In exchange, the cost no longer grows one Git process per untracked file and Git can detect renames correctly.

Validation

• vp test run apps/server/src/vcs/GitVcsDriverCore.test.ts (54 tests)
• targeted lint and formatting checks
• server typecheck
• current web UI integrated pass with a disposable rename fixture

Generated with GPT-5.6-Sol via T3 Code's Codex harness.

Note

Fix file rename detection in GitVcsDriverCore review diffs

• Replaces the manual tracked+untracked diff concatenation in getReviewDiffPreview with a unified diff pipeline that adds --find-renames to all tracked git diff calls
• readUnifiedWorkingTreeReviewDiff stages untracked files with --intent-to-add into a temp copy of the index (via GIT_INDEX_FILE) so the real index is never mutated, and filters untracked paths that have staged deletions
• readWorkingTreeReviewDiff prefers the unified path and falls back to the old concatenated approach on failure; truncation state is propagated through all paths
• Adds integration tests for unstaged rename detection, staged deletion preservation, and untracked file visibility before the first commit
• Risk: readUnifiedWorkingTreeReviewDiff sets GIT_INDEX_FILE to a temp file; if cleanup fails, subsequent git commands in the process could target a stale index. The scoped context should restore the env var, but reviewers should confirm the temp file is removed on all exit paths

^{Macroscope summarized 49a8e8e.}

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Note

Medium Risk
Touches Git review-diff generation and uses a copied index plus GIT_INDEX_FILE/intent-to-add. The real index is not modified and failures fall back to the old path, but incorrect path filtering could still mis-render staged deletions or untracked files.

Overview
Working-tree review diffs now treat filesystem renames as a single rename (including edits) instead of an unrelated delete plus add.

When untracked files exist, the driver copies the Git index into a scoped temp file, intent-to-adds those paths there, and runs one git diff --find-renames against HEAD. The real index is never written. Staged deletions whose paths still exist on disk are excluded from that add so they stay deletions. If temp-index setup fails, it falls back to the previous separate tracked/untracked patches.

Tests cover rename-with-edit without mutating a split index, staged deletions, and untracked files before the first commit.

^{Reviewed by Cursor Bugbot for commit 49a8e8e. Bugbot is set up for automated code reviews on this repo. Configure here.}

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[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 2 potential issues.

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[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — The server-side review-diff pipeline is substantially reworked for worktrees with untracked files, including temporary Git-index handling, staged-deletion filtering, fallback logic, and new rename rendering. Although the scope is confined to review previews and includes regression coverage, the runtime behavior and implementation complexity merit human review.

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