fix: block sensitive symlink targets

internal/codexhome/bounds_test.go

@@ -1,6 +1,7 @@
 package codexhome
 
 import (
+	"errors"
 	"os"
 	"path/filepath"
 	"testing"
@@ -91,3 +92,22 @@ func TestResolveAgentTOMLRejectsUnsafeNames(t *testing.T) {
 		})
 	}
 }
+
+func TestResolveAgentTOMLRejectsSymlinkToAuthJSON(t *testing.T) {
+	home := filepath.Join(t.TempDir(), ".codex")
+	agentsDir := filepath.Join(home, "agents")
+	if err := os.MkdirAll(agentsDir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(home, "auth.json"), []byte("{}"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Symlink("../auth.json", filepath.Join(agentsDir, "demo.toml")); err != nil {
+		t.Fatal(err)
+	}
+
+	_, err := ResolveAgentTOML(home, "demo.toml")
+	if !errors.Is(err, ErrForbiddenPath) {
+		t.Fatalf("expected ErrForbiddenPath, got %v", err)
+	}
+}