Use STATUSLINE_WIDTH env var for reliable width detection

term.GetSize returns unreliable values when running inside Claude Code
over SSH. Replace the hardcoded statuslineWidthOffset with STATUSLINE_WIDTH
env var (set in Claude Code settings), falling back to terminal detection,
then 80 columns.

main.go

@@ -15,7 +15,7 @@ import (
 	"golang.org/x/term"
 )
 
-const statuslineWidthOffset = 7
+const defaultStatuslineWidth = 80
 
 // TokenUsage tracks context window token consumption.
 type TokenUsage struct {
@@ -117,7 +117,7 @@ func run(r *bufio.Reader, w *strings.Builder) error {
 	rightVisible := stripANSI(right)
 
 	// Get terminal width
-	termWidth := getTerminalWidth() - statuslineWidthOffset
+	termWidth := getTerminalWidth()
 
 	// Calculate and apply padding
 	padding := calculatePadding(leftVisible, rightVisible, termWidth)
@@ -212,30 +212,30 @@ func getGitInfo(cwd string) string {
 	return fmt.Sprintf(" git:(%s)", branch)
 }
 
-// termWidthFunc returns the terminal width.
-// Tries stderr and stdin as fallbacks since stdout is typically piped
-// when Claude Code captures the status line output.
+// termWidthFunc returns the usable status line width.
+// Checks STATUSLINE_WIDTH env var first (set in Claude Code settings),
+// then tries terminal detection on stderr/stdin/stdout, then falls back
+// to defaultStatuslineWidth.
 // Replaced in tests to avoid depending on a real TTY.
 var termWidthFunc = func() (int, error) {
+	if sw := os.Getenv("STATUSLINE_WIDTH"); sw != "" {
+		var w int
+		if _, err := fmt.Sscanf(sw, "%d", &w); err == nil && w > 0 {
+			return w, nil
+		}
+	}
 	for _, fd := range []uintptr{os.Stderr.Fd(), os.Stdin.Fd(), os.Stdout.Fd()} {
 		if width, _, err := term.GetSize(int(fd)); err == nil {
 			return width, nil
 		}
 	}
-	// Fall back to COLUMNS env var
-	if cols := os.Getenv("COLUMNS"); cols != "" {
-		var w int
-		if _, err := fmt.Sscanf(cols, "%d", &w); err == nil && w > 0 {
-			return w, nil
-		}
-	}
 	return 0, errors.New("no terminal detected")
 }
 
 func getTerminalWidth() int {
 	width, err := termWidthFunc()
 	if err != nil {
-		return 80
+		return defaultStatuslineWidth
 	}
 	return width
 }