Write a GPU kernel that masks logits to a grammar's DFA during decoding, with under 1% overhead.
Constrained JSON/grammar decoding usually means a Python callback per token, which serializes the GPU. The staff answer keeps the DFA on-device and turns the mask into a single coalesced gather.
Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.
Constrained JSON/grammar decoding usually means a Python callback per token, which serializes the GPU. The staff answer keeps the DFA on-device and turns the mask into a single coalesced gather.
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.
