A frontend is a container image that BuildKit runs to convert your build definition (Dockerfile, YAML, JSON, HCL, whatever) into LLB. The frontend receives the build context and the build file through the BuildKit Gateway API, and returns a serialized LLB graph.
You might assume this pattern is inherent to streaming. It isn't. The reader acquisition, the lock management, and the { value, done } protocol are all just design choices, not requirements. They are artifacts of how and when the Web streams spec was written. Async iteration exists precisely to handle sequences that arrive over time, but async iteration did not yet exist when the streams specification was written. The complexity here is pure API overhead, not fundamental necessity.
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NYT Pips hints, answers for February 27, 2026
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