Emphasis does not name the agent in the passive. لَيُبَاعَنَّ retains the passive imperfect’s internal long ā and contrasts with the active لَيَبِيعَنَّ.
PositionPassive with heavy nūn
هُوَلَيُبَاعَنَّ
هُمَا (م)لَيُبَاعَانِّ
هُمْلَيُبَاعُنَّ
هِيَلَتُبَاعَنَّ
هُمَا (ف)لَتُبَاعَانِّ
هُنَّلَيُبَعْنَانِّ
أَنْتَلَتُبَاعَنَّ
أَنْتُمَا (م)لَتُبَاعَانِّ
أَنْتُمْلَتُبَاعُنَّ
أَنْتِلَتُبَاعِنَّ
أَنْتُمَا (ف)لَتُبَاعَانِّ
أَنْتُنَّلَتُبَعْنَانِّ
أَنَالَأُبَاعَنَّ
نَحْنُلَنُبَاعَنَّ
Attaching an emphatic ending does not by itself change active into passive or vice versa. The voice contrast lies in the verb pattern as well as the affix.