I'm wondering if what TCP wants is an ICMP side channel where the link layer can say, "for the TCP session started with cookie Z, you should know that X packet

I'm wondering if what TCP wants is an ICMP side channel where the link layer can say, "for the TCP session started with cookie Z, you should know that X packet drops in Y seconds are normal and should not count against the bandwidth estimation". Or even more precisely, "expect up to Z drops during this X ms window every Y ms".