embeddings

Packing removes padding but puts different requests' tokens side by side in one tensor, so the kernel's tile boundaries no longer match sequence boundaries. The answer shows the indexing and a bug that a causal test can never catch.

Offline work changes the regime: the batch is as big as memory allows, latency is irrelevant, and output tokens stop being expensive. The answer prices both passes in GPU-hours, finds which one is the bill, and cuts it.