Implement milestone 6b workbench routing skeleton

internal/shell/debug/logger.go

@@ -0,0 +1,95 @@
+// Package debug provides a debug logger that writes to a file.
+// Enabled with --debug CLI flag.
+package debug
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"path/filepath"
+	"sync"
+	"time"
+)
+
+var (
+	logger *log.Logger
+	mu     sync.Mutex
+	enabled bool
+)
+
+// Init initializes the debug logger. If --debug is present in args,
+// it writes to ~/.local/share/verstak/debug/verstak-YYYY-MM-DD-HHMMSS.log.
+// Returns true if debug mode is enabled.
+func Init(args []string) bool {
+	mu.Lock()
+	defer mu.Unlock()
+
+	for _, a := range args {
+		if a == "--debug" {
+			enabled = true
+			break
+		}
+	}
+
+	if !enabled {
+		return false
+	}
+
+	// Create log directory
+	logDir := filepath.Join(os.Getenv("HOME"), ".local", "share", "verstak", "debug")
+	if err := os.MkdirAll(logDir, 0755); err != nil {
+		log.Printf("[debug] failed to create log dir %s: %v", logDir, err)
+		// Fallback to /tmp
+		logDir = filepath.Join(os.TempDir(), "verstak-debug")
+		os.MkdirAll(logDir, 0755)
+	}
+
+	// Create log file with timestamp
+	timestamp := time.Now().Format("2006-01-02-150405")
+	logFile := filepath.Join(logDir, fmt.Sprintf("verstak-%s.log", timestamp))
+
+	f, err := os.OpenFile(logFile, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0644)
+	if err != nil {
+		log.Printf("[debug] failed to open log file %s: %v", logFile, err)
+		return true // Still enabled, but logging to stderr
+	}
+
+	// Write to both file and stderr
+	mw := io.MultiWriter(f, os.Stderr)
+	logger = log.New(mw, "", log.LstdFlags|log.Lmicroseconds)
+
+	log.Printf("[debug] logger initialized: %s", logFile)
+	return true
+}
+
+// IsEnabled returns whether debug mode is active.
+func IsEnabled() bool {
+	mu.Lock()
+	defer mu.Unlock()
+	return enabled
+}
+
+// Logf writes a formatted debug message.
+func Logf(format string, v ...interface{}) {
+	mu.Lock()
+	defer mu.Unlock()
+	if !enabled {
+		return
+	}
+	if logger != nil {
+		logger.Printf(format, v...)
+	}
+}
+
+// Log writes a debug message.
+func Log(v ...interface{}) {
+	mu.Lock()
+	defer mu.Unlock()
+	if !enabled {
+		return
+	}
+	if logger != nil {
+		logger.Println(v...)
+	}
+}