Chunk 12.0

This chunk completed the **Phase 3 E2E GPU testing** campaign for the cuzk cross-sector batching feature. Starting from the baseline single-proof test that was already running, we first analyzed the baseline memory data (peak 202.9 GiB RSS during synthesis, ~45 GiB idle with SRS resident), then stopped the baseline daemon and launched a new daemon with `max_batch_size=2`. Four systematic tests were executed against the RTX 5070 Ti with real 32 GiB PoRep data: (1) **timeout flush** verified the BatchCollector correctly flushes a single proof after the 30,000ms `max_batch_wait_ms` (actual: 30,258ms), (2) **batch=2** demonstrated two concurrent proofs being synthesized together as 20 circuits in 55.3s (identical to 10 circuits for a single proof), proving full synthesis amortization, (3) **3-proof overflow** confirmed correct batch-of-2 + overflow behavior with pipeline overlap between synthesis and GPU phases, and (4) **WinningPoSt bypass** verified non-batchable types skip the collector entirely (0.8s total). The quantitative results are compelling: batch=2 achieves **1.42x throughput improvement** (62.7s/proof amortized vs 89s baseline), with synthesis cost fully shared across sectors while GPU time scales linearly (34s per sector). Memory peaks at ~360 GiB for batch=2 (vs 203 GiB single), closely matching the predicted ~408 GiB estimate when accounting for SRS overhead. All proof outputs were valid 1920-byte Groth16 proofs, and the daemon logs confirmed every stage of the Phase 3 architecture — `synth_batch_full`, `synthesize_porep_c2_multi{num_sectors=2}`, `total_circuits=20`, and `split_batched_proofs` producing correct per-sector boundaries. The results were compiled into `cuzk-project.md` and committed as `353e4c2a`, marking Phase 3 as fully validated and documented. The conversation concluded by noting Phase 3 is complete and ready for the next phase (Phase 4: Compute Quick Wins) pending direction.

The Validation of Cross-Sector Batching: How Phase 3 of the cuzk SNARK Proving Engine Was Systematically Tested and Proven 2513 words

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