An endpoint's ack_delay_exponent is conveyed in its transport parameters. An endpoint can receive an ACK before it receives transport parameters from the peer. For example, a client may read an ACK in an Initial packet before it receives transport parameters in a Handshake packet.
RFC 9000 isn't clear (IMO) on how to interpret an ACK Delay fields prior to receiving transport parameters. Valid options might be to treat all ACK Delay fields as 0 until an ack_delay_exponent is known, or to use the default value of 3 for Initial and Handshake packets and only apply the transport parameter for 1-RTT packets. Am I missing text somewhere which explains the expected behavior?
