fix(preview): expand tabs based on current line position

Tab characters are now expanded to reach the next tab stop based on
the current display position in the line, rather than always expanding
to exactly 4 spaces. This matches standard terminal behavior where
tabs align to fixed column positions.

For example, with TabWidth=4:
- Position 1: tab expands to 3 spaces (reaches column 4)
- Position 3: tab expands to 1 space (reaches column 4)
- Position 4: tab expands to 4 spaces (reaches column 8)

Author: root

src/internal/common/string_function.go

@@ -228,6 +228,8 @@ func IsTextFile(filename string) (bool, error) {
 // This function should better not be broken into multiple functions
 func MakePrintableWithEscCheck(line string, allowEsc bool) string { //nolint: gocognit // See above
 	var sb strings.Builder
+	// Track current display width for proper tab expansion
+	curWidth := 0
 	for _, r := range line {
 		if r == utf8.RuneError {
 			continue
@@ -236,13 +238,17 @@ func MakePrintableWithEscCheck(line string, allowEsc bool) string { //nolint: go
 		// It is multi-byte in UTF-8, But it has zero display width
 		if r == NonBreakingSpace {
 			sb.WriteRune(r)
+			curWidth++
 			continue
 		}
 		// It needs to be handled separately since considered a space,
 		// Since we are using ansi.StringWidth() for truncation, and \t is
 		// considered zero width
 		if r == '\t' {
-			sb.WriteString("    ")
+			// Expand tab to reach next tab stop based on current position
+			spacesNeeded := TabWidth - (curWidth % TabWidth)
+			sb.WriteString(strings.Repeat(" ", spacesNeeded))
+			curWidth += spacesNeeded
 			continue
 		}
 		if r == EscapeChar {
@@ -259,10 +265,17 @@ func MakePrintableWithEscCheck(line string, allowEsc bool) string { //nolint: go
 				r = ' '
 			}
 			sb.WriteRune(r)
+			curWidth += ansi.StringWidth(string(r))
 			continue
 		}
 		if unicode.IsGraphic(r) || r == rune('\n') {
 			sb.WriteRune(r)
+			if r != rune('\n') {
+				curWidth++
+			} else {
+				// Reset width on newline
+				curWidth = 0
+			}
 		}
 	}
 	return sb.String()

src/internal/common/string_function_test.go

@@ -176,7 +176,13 @@ func TestMakePrintable(t *testing.T) {
 		{"", ""},
 		{"hello", "hello"},
 		{"abcdABCD0123~!@#$%^&*()_+-={}|:\"<>?,./;'[]", "abcdABCD0123~!@#$%^&*()_+-={}|:\"<>?,./;'[]"},
-		{"Horizontal Tab and NewLine\t\t\n\n", "Horizontal Tab and NewLine        \n\n"},
+		{"Horizontal Tab and NewLine\t\t\n\n", "Horizontal Tab and NewLine      \n\n"},
+		// Tab expansion tests - tabs should expand to reach next tab stop (TabWidth=4)
+		{"a\tb", "a   b"},        // Position 1: need 3 spaces to reach position 4
+		{"ab\tc", "ab  c"},       // Position 2: need 2 spaces to reach position 4
+		{"abc\td", "abc d"},      // Position 3: need 1 space to reach position 4
+		{"abcd\te", "abcd    e"}, // Position 4: need 4 spaces to reach position 8
+		{"a\tb\tc", "a   b   c"}, // Position 1: 3 spaces, then position 4: 4 spaces to reach 8
 		{"(NBSP)\u00a0\u00a0\u00a0\u00a0;", "(NBSP)\u00a0\u00a0\u00a0\u00a0;"},
 		{"\x0b(Vertical Tab)", "(Vertical Tab)"},
 		{"\x0d(CR)", "(CR)"},