snapshotChunkCeiling

Upper bound on the raw state bytes carried in a single §7 InstallSnapshot chunk. A fabric with a tighter framing limit shrinks chunks automatically: when the transport publishes a RaftTransport.maxPayloadBytes, the engine takes the lesser of this and what that budget leaves once the envelope reserve and the chunk's own length header are paid. Raw and wire bytes are not the same unit and never were: they differed by up to a factor of two until #2160, and since it by a 1–5 byte header that steps with the chunk's length, which the engine charges for explicitly rather than hoping the envelope reserve covers it (#2150).

Validated at construction to at least 1 (#2839). With no published budget the engine uses this value as given, so it is the chunk size itself: at 0 every chunk is empty and the transfer never finishes, and a negative value makes the slice throw on the actor loop. The engine's own maxOf(1, …) floor never covered either case — it sits on the budgeted path only.