Chunk 10.0

In this session, the assistant completed the remaining Phase 2 pipeline work by first committing the batch-mode pipeline rewrite (all 4 proof types with inlined circuit construction) that had been developed but uncommitted, then implementing the core architectural goal: true async overlap between CPU-bound synthesis and GPU-bound proving. The engine was restructured from per-GPU workers that sequentially synthesized and proved each proof, to a two-stage pipeline with a dedicated synthesis task feeding a bounded `tokio::sync::mpsc` channel (capacity controlled by `synthesis_lookahead` config), with per-GPU workers consuming synthesized jobs from the channel. This allows synthesis of proof N+1 to overlap with GPU proving of proof N, providing backpressure via the bounded channel to prevent OOM. An E2E GPU test on the RTX 5070 Ti with 3 consecutive 32 GiB PoRep C2 proofs validated the architecture: total time dropped from an estimated ~270s (sequential) to 212.7s, with steady-state throughput improving from ~90s/proof to ~60s/proof (1.27x speedup). The logs confirmed the overlap pattern — synthesis of each subsequent proof began while the GPU was still processing the previous one. All 15 unit tests pass with zero warnings, the git state is clean with 3 Phase 2 commits (bellperson fork, batch pipeline, async overlap), and the project is ready to move to Phase 3 (cross-sector batching) per the roadmap.

The Async Overlap Pipeline: How Phase 2 of the cuzk Proving Engine Transformed Sequential Proof Generation into a Concurrent Powerhouse 2311 words

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