Simplify session lifecycle and MCP cleanup

internal/harness/session.go

@@ -210,19 +210,19 @@ func (s *Session) WaitForStable(timeout time.Duration) error {
 }
 
 func (s *Session) WaitForText(text string, timeout time.Duration) error {
-	deadline := time.Now().Add(timeout)
-	for time.Now().Before(deadline) {
+	return pollUntil(timeout, 25*time.Millisecond, func() (bool, error) {
 		screen, err := s.Screen()
 		if err != nil {
-			return err
+			return false, err
 		}
 		if strings.Contains(screen, text) {
-			return nil
+			return true, nil
 		}
-		time.Sleep(25 * time.Millisecond)
-	}
-	screen, _ := s.Screen()
-	return fmt.Errorf("text %q not found before timeout; screen:\n%s", text, screen)
+		return false, nil
+	}, func() error {
+		screen, _ := s.Screen()
+		return fmt.Errorf("text %q not found before timeout; screen:\n%s", text, screen)
+	})
 }
 
 func (s *Session) WaitForRegex(pattern string, timeout time.Duration) error {
@@ -230,19 +230,31 @@ func (s *Session) WaitForRegex(pattern string, timeout time.Duration) error {
 	if err != nil {
 		return err
 	}
-	deadline := time.Now().Add(timeout)
-	for time.Now().Before(deadline) {
+	return pollUntil(timeout, 25*time.Millisecond, func() (bool, error) {
 		screen, err := s.Screen()
 		if err != nil {
-			return err
+			return false, err
 		}
 		if re.MatchString(screen) {
-			return nil
+			return true, nil
 		}
-		time.Sleep(25 * time.Millisecond)
+		return false, nil
+	}, func() error {
+		screen, _ := s.Screen()
+		return fmt.Errorf("regex %q not found before timeout; screen:\n%s", pattern, screen)
+	})
+}
+
+func pollUntil(timeout, interval time.Duration, check func() (bool, error), timeoutErr func() error) error {
+	deadline := time.Now().Add(timeout)
+	for time.Now().Before(deadline) {
+		ok, err := check()
+		if err != nil || ok {
+			return err
+		}
+		time.Sleep(interval)
 	}
-	screen, _ := s.Screen()
-	return fmt.Errorf("regex %q not found before timeout; screen:\n%s", pattern, screen)
+	return timeoutErr()
 }
 
 func (s *Session) MCPCall(method string, params json.RawMessage) (json.RawMessage, error) {