When do you use long context, RAG, or prompt caching, and what are the failure modes of each?
Million-token windows didn't kill RAG; they changed when you reach for it. The decision rule that holds up in production, and the silent failure each option hides behind a confident answer.
Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.
Million-token windows didn't kill RAG; they changed when you reach for it. The decision rule that holds up in production, and the silent failure each option hides behind a confident answer.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
