Fates of impactors during their accretion onto grain-free proto-planetary envelopes at 0.1 AU. The red zone indicates thermal ablation, the dominant disruption process for pebbles. It shows a proportional relationship with planetary mass, and agrees with our analytical expression of Eq. (19). The grey zone indicates breakup. Small km-sized planetesimals are very susceptible to fragmentation, whereas 100 km planetesimals are almost completely resistant to it.