Isobaric: Bounding Cold HTTP/1.1 GET Admission with XDP Payload Suppression

Isobaric is an eBPF/XDP prototype for bounding cold HTTP/1.1 GET payload admission during cache-stampede conditions. The mechanism suppresses duplicate cleartext HTTP/1.1 GET payloads for an active cache key at a dedicated backend ingress boundary. Followers recover through TCP retransmission after cache warmup.This v1.1.1 preprint compares no coalescing, event-driven userspace single-flight, and XDP suppression across 30 paired 1,000-client repetitions at each of 1, 10, and 100 simultaneously cold keys, plus 20 HTTPS-originated post-TLS repetitions. The result is cold GET payload suppression at a cleartext backend boundary, not general HTTPS, HTTP/2/gRPC, or HTTP/3 processing.The accompanying reproducibility package contains raw run records, validation files, source snapshots, summary data, and rerun instructions.