Chunk 18.0

## Summary This chunk focused on three major advances: **PCE disk persistence**, **Phase 6 slotted pipeline design**, and **daemon integration**. First, PCE serialization was implemented with a raw binary format that writes CSR vectors as bulk byte dumps (32-byte header + length-prefixed raw arrays), achieving a 5.4× load speedup over bincode (9.2s vs 49.9s from tmpfs for 25.7 GiB). The daemon now preloads PCE from disk at startup (`preload_pce_from_disk()`), saves extracted PCE automatically, and triggers background PCE extraction after the first old-path synthesis — eliminating the first-proof penalty entirely. A Phase 6 design document (`c2-optimization-proposal-6.md`) was written analyzing the slotted partition pipeline, showing that slot_size=2 yields 41s single-proof latency (vs 69.5s batch) with 54 GiB working set (vs 136 GiB), enabled by the discovery that GPU per-circuit cost is ~3.4s with near-zero fixed overhead. The architectural discussion shifted toward finer-grained pipelining: instead of synthesizing all 10 partitions in parallel then GPU-proving them in one batch, the slotted pipeline overlaps synthesis and GPU at partition granularity. This reduces peak memory by 2.5× while improving single-proof latency by 1.7×, and in steady state with multiple proofs queued, GPU utilization stays at ~96% while memory stays bounded. The implementation began with `prove_porep_c2_slotted()` but revealed that `synthesize_porep_c2_partition` redundantly deserializes C1 JSON per call — a refactor to share parsed data across slots is needed. All changes were committed at `6b0121fa` alongside the project doc updates with j=2 parallel pipeline benchmark data.

From 50 Seconds to 9: How PCE Disk Persistence, Daemon Integration, and a Slotted Pipeline Reshaped a 200 GiB Proving Engine 3597 words

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