Constant MAX_CLIENT_CONTROL_FRAME 

pub const MAX_CLIENT_CONTROL_FRAME: u32 = _ /* 4_096u32 */;

Frame ceiling for every cdn/client/v1 message except ClientMessage::ChunkData, in payload bytes (ADR 013 § Wire Framing).

The node reads a StreamRequest and every later payment proof against it, and a payer reads the StreamResponse against it. The largest legitimate message is a StreamRequest with a client binding and a capability: 301 bytes, since every signature on the wire is a 65-byte EOA signature. The ceiling leaves headroom for Tier-1 extension fields and refuses a larger frame before the reader buffers it. It is also the wire bound on owner_signature, which decode checks only for being non-empty. The client_control_frame_ceiling_holds_the_largest_message test pins the margin.