Fix all golangci-lint warnings

- Extract writeStagedBlameFile() to reduce nestif complexity in blame.go
- Combine param types in FileBlame signature (gocritic)
- Handle errcheck/gosec on temp file cleanup paths
- Extract deletePlaceholderVisualHeight() to reduce nestif in annotate.go
- Remove stale //nolint:gosec directives from diff.go and diff_test.go
- Pre-allocate slices in directory.go, fallback.go, theme.go, filetree.go,
  mdtoc.go, and model_test.go; preserve nil-vs-empty semantics in fallback.go

Author: melonamin

diff/blame.go

@@ -19,28 +19,14 @@ type BlameLine struct {
 // For unstaged single-ref diffs this is the worktree; for two-ref diffs this is the target ref.
 // For staged diffs this is the index snapshot. The returned map is keyed by 1-based line
 // number (matching DiffLine.NewNum).
-func (g *Git) FileBlame(ref string, file string, staged bool) (map[int]BlameLine, error) {
+func (g *Git) FileBlame(ref, file string, staged bool) (map[int]BlameLine, error) {
 	args := []string{"blame", "--line-porcelain"}
 	if staged {
-		indexContent, err := g.runGit("show", ":"+file)
+		tmpName, err := g.writeStagedBlameFile(file)
 		if err != nil {
-			return nil, fmt.Errorf("read index contents for %s: %w", file, err)
+			return nil, err
 		}
-
-		tmp, err := os.CreateTemp("", "revdiff-blame-*")
-		if err != nil {
-			return nil, fmt.Errorf("create temp blame file for %s: %w", file, err)
-		}
-		tmpName := tmp.Name()
-		defer os.Remove(tmpName)
-		if _, err := tmp.WriteString(indexContent); err != nil {
-			tmp.Close()
-			return nil, fmt.Errorf("write temp blame file for %s: %w", file, err)
-		}
-		if err := tmp.Close(); err != nil {
-			return nil, fmt.Errorf("close temp blame file for %s: %w", file, err)
-		}
-
+		defer os.Remove(tmpName) //nolint:errcheck // best-effort temp file cleanup
 		args = append(args, "--contents", tmpName)
 	} else if targetRef := blameTargetRef(ref); targetRef != "" {
 		args = append(args, targetRef)
@@ -53,6 +39,27 @@ func (g *Git) FileBlame(ref string, file string, staged bool) (map[int]BlameLine
 	return parseBlame(out)
 }
 
+// writeStagedBlameFile writes the staged (index) contents of file to a temp file
+// and returns its path. The caller is responsible for removing the temp file.
+func (g *Git) writeStagedBlameFile(file string) (string, error) {
+	indexContent, err := g.runGit("show", ":"+file)
+	if err != nil {
+		return "", fmt.Errorf("read index contents for %s: %w", file, err)
+	}
+	tmp, err := os.CreateTemp("", "revdiff-blame-*")
+	if err != nil {
+		return "", fmt.Errorf("create temp blame file for %s: %w", file, err)
+	}
+	if _, err := tmp.WriteString(indexContent); err != nil {
+		tmp.Close() //nolint:gosec // best-effort close in error path
+		return "", fmt.Errorf("write temp blame file for %s: %w", file, err)
+	}
+	if err := tmp.Close(); err != nil {
+		return "", fmt.Errorf("close temp blame file for %s: %w", file, err)
+	}
+	return tmp.Name(), nil
+}
+
 func blameTargetRef(ref string) string {
 	parts := strings.Split(ref, "..")
 	if len(parts) != 2 || parts[0] == "" || parts[1] == "" {

diff/diff.go

@@ -92,7 +92,7 @@ func (g *Git) diffArgs(ref string, staged bool) []string {
 
 // runGit executes a git command in the working directory and returns its output.
 func (g *Git) runGit(args ...string) (string, error) {
-	cmd := exec.CommandContext(context.Background(), "git", args...) //nolint:gosec // git args are constructed internally
+	cmd := exec.CommandContext(context.Background(), "git", args...)
 	cmd.Dir = g.workDir
 	out, err := cmd.Output()
 	if err != nil {

diff/diff_test.go

@@ -325,7 +325,7 @@ func writeFile(t *testing.T, dir, name, content string) {
 
 func gitCmd(t *testing.T, dir string, args ...string) {
 	t.Helper()
-	cmd := exec.Command("git", args...) //nolint:gosec // test helper
+	cmd := exec.Command("git", args...)
 	cmd.Dir = dir
 	out, err := cmd.CombinedOutput()
 	require.NoError(t, err, "git %v failed: %s", args, string(out))

diff/directory.go

@@ -40,7 +40,7 @@ func (dr *DirectoryReader) ChangedFiles(_ string, _ bool) ([]string, error) {
 		return nil, fmt.Errorf("git ls-files: %w", err)
 	}
 
-	var files []string
+	files := make([]string, 0, strings.Count(string(out), "\x00"))
 	for entry := range strings.SplitSeq(string(out), "\x00") {
 		if entry == "" {
 			continue

diff/fallback.go

@@ -160,14 +160,20 @@ func NewFileReader(files []string, workDir string) *FileReader {
 
 // ChangedFiles returns the file list, resolved against workDir, filtered to only those that exist on disk.
 func (r *FileReader) ChangedFiles(_ string, _ bool) ([]string, error) {
-	var result []string
+	if len(r.files) == 0 {
+		return nil, nil
+	}
+	result := make([]string, 0, len(r.files))
 	for _, f := range r.files {
 		resolved := resolvePath(r.workDir, f)
 		if _, err := os.Stat(resolved); err != nil {
 			continue // skip files that don't exist
 		}
 		result = append(result, resolved)
 	}
+	if len(result) == 0 {
+		return nil, nil
+	}
 	return result, nil
 }
 

theme/theme.go

@@ -223,7 +223,7 @@ func List(themesDir string) ([]string, error) {
 		return nil, fmt.Errorf("reading themes dir: %w", err)
 	}
 
-	var names []string
+	names := make([]string, 0, len(entries))
 	for _, e := range entries {
 		if e.IsDir() {
 			continue

ui/annotate.go

@@ -285,20 +285,7 @@ func (m Model) cursorViewportY() int {
 		// delete-only placeholders render synthetic text ("⋯ N lines deleted"), not original content.
 		// use placeholder text for wrapping to stay in sync with renderDeletePlaceholder.
 		if m.isDeleteOnlyPlaceholder(i, hunks) {
-			if m.wrapMode {
-				text := m.deletePlaceholderText(i)
-				gutterExtra := 0
-				if m.lineNumbers {
-					gutterExtra = m.lineNumGutterWidth()
-				}
-				if m.hasBlameGutter() {
-					gutterExtra += m.blameGutterWidth()
-				}
-				wrapWidth := m.diffContentWidth() - wrapGutterWidth - gutterExtra
-				y += len(m.wrapContent(text, wrapWidth))
-			} else {
-				y++ // placeholder is always 1 row when not wrapping
-			}
+			y += m.deletePlaceholderVisualHeight(i)
 			continue
 		}
 		y += m.wrappedLineCount(i) // the diff line (may occupy multiple visual rows when wrapping)

ui/collapsed.go

@@ -173,6 +173,24 @@ func (m Model) deletePlaceholderText(hunkStart int) string {
 	return fmt.Sprintf("⋯ %d lines deleted", count)
 }
 
+// deletePlaceholderVisualHeight returns the number of visual rows a delete-only placeholder
+// occupies, accounting for wrap mode and gutter widths.
+func (m Model) deletePlaceholderVisualHeight(hunkStart int) int {
+	if !m.wrapMode {
+		return 1
+	}
+	text := m.deletePlaceholderText(hunkStart)
+	gutterExtra := 0
+	if m.lineNumbers {
+		gutterExtra = m.lineNumGutterWidth()
+	}
+	if m.hasBlameGutter() {
+		gutterExtra += m.blameGutterWidth()
+	}
+	wrapWidth := m.diffContentWidth() - wrapGutterWidth - gutterExtra
+	return len(m.wrapContent(text, wrapWidth))
+}
+
 // renderDeletePlaceholder renders a placeholder line for a delete-only hunk in collapsed mode.
 // shows "⋯ N lines deleted" with remove styling so users know deletions exist and can expand with '.'.
 // when search is active, matching placeholders use search highlight instead of remove styling.

ui/filetree.go

@@ -57,7 +57,7 @@ func (ft *fileTree) buildEntries(files []string) []treeEntry {
 	}
 	sort.Strings(dirs)
 
-	var entries []treeEntry
+	entries := make([]treeEntry, 0, len(dirs)+len(files))
 	for _, dir := range dirs {
 		// add directory entry
 		dirName := dir

ui/mdtoc.go

@@ -28,7 +28,7 @@ type mdTOC struct {
 // fence tracking is CommonMark-compliant: closing fence must use the same character
 // with at least the same length as the opening fence.
 func parseTOC(lines []diff.DiffLine, filename string) *mdTOC {
-	var entries []tocEntry
+	entries := make([]tocEntry, 0, len(lines))
 	var fenceChar rune // 0 when outside code block, '`' or '~' when inside
 	var fenceLen int   // length of the opening fence sequence