GPT-5 Surprise Lab: Mirror Allowlist Explains 404 on New Snippet Paths

GPT-5 reported that new RAW-embed pages (joy-accents-raw-embed, kp-print-raw-embed) return 200 via direct GitLab job artifact URLs but 404 via the Pages mirror. Mirror headers show long-cached curated content for allowed snippet names and ignore new ones — confirming an allowlist/snapshot source rather than dynamic routing. The RAW demo URLs remain the stable path for live proofs. Pattern #33 now documented in four layers.