SyncInbound runs once per inbound and unconditionally overwrites the canonical clients.Flow column. A non-flow inbound (Hysteria, WS, gRPC) strips flow to "", so when it syncs after a VLESS Reality inbound the column is wiped, and the hydrate endpoint returned that empty value — the edit form loaded a blank flow for multi-inbound clients (#4792).
Derive the hydrate flow from the first flow-capable client_inbounds.flow_override instead, which is always correct and order-independent. A non-empty guard in SyncInbound was rejected because it would make flow impossible to clear.
Closes#4792