Context engineering: what fits and what gets dropped

"Context engineering" is getting used as a rebrand for prompt writing, and that undersells it into uselessness. The actual discipline is deciding, every single turn, what earns a place in a bounded window and what gets evicted — and living with the fact that every eviction is a bet you're making about the future of a run you haven't finished yet. Here's the physical constraint underneath the buzzword, the packing decision that's actually hard, what it costs to get it wrong, and how to test whether your packing policy works.