feat: open the file manager in the user's home directory

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/agent/fs.go

@@ -9,7 +9,9 @@ import (
 	"io"
 	"os"
 	"os/exec"
+	"os/user"
 	"path/filepath"
+	"runtime"
 	"sort"
 	"strings"
 	"unicode/utf8"
@@ -79,8 +81,18 @@ func fsList(path string) (proto.FSListResult, error) {
 	if path == "" {
 		path = "/"
 	}
+	// "~" / "~name" is where the file manager starts: the home directory, or
+	// the root when there is none to open.
+	home := strings.HasPrefix(path, "~") && !strings.Contains(path, "/")
+	if home {
+		path = homeDir(path[1:])
+	}
 	abs, _ := filepath.Abs(path)
 	entries, err := os.ReadDir(abs)
+	if err != nil && home && abs != "/" {
+		abs = "/"
+		entries, err = os.ReadDir(abs)
+	}
 	if err != nil {
 		return proto.FSListResult{}, err
 	}
@@ -222,3 +234,30 @@ func fsZip(paths []string, dest string) (any, error) {
 	}
 	return map[string]string{"dest": dest}, nil
 }
+
+// homeDir returns the home directory of the named user ("" = the user the
+// agent runs as), or "/" when it cannot be told.
+func homeDir(name string) string {
+	if name != "" {
+		if validUserName(name) {
+			if u, err := user.Lookup(name); err == nil && u.HomeDir != "" {
+				return u.HomeDir
+			}
+		}
+		return "/"
+	}
+	if u, err := user.Current(); err == nil && u.HomeDir != "" {
+		return u.HomeDir
+	}
+	if h := os.Getenv("HOME"); h != "" {
+		return h
+	}
+	// A root service often has neither a passwd entry we can read nor $HOME.
+	if os.Geteuid() == 0 {
+		if runtime.GOOS == "darwin" {
+			return "/var/root"
+		}
+		return "/root"
+	}
+	return "/"
+}