Chunk 7.0

In this chunk, the assistant completed Phase 1 by implementing the `gen-vanilla` command in `cuzk-bench`, which generates vanilla proof test data for WinningPoSt, WindowPoSt, and SnapDeals from sealed sector data on disk. This required adding `filecoin-proofs-api` as an optional dependency behind a `gen-vanilla` feature flag, implementing CID commitment parsing via the `cid` crate, and writing three sub-subcommands that call CPU-only vanilla proof generation functions. The implementation was validated against the golden test data at `/data/32gbench/`, producing correct outputs (164 KB WinningPoSt proof, 25 KB WindowPoSt proof, 12 MB SnapDeals partition proofs). Five new unit tests were added, and the milestone was committed as `9d8453c3`. The assistant then moved to Phase 2, starting with a deep analysis of bellperson's internal architecture, discovering that the synthesis/GPU split already exists internally as `synthesize_circuits_batch()` and the GPU-phase code in `create_proof_batch_priority_inner`. A detailed Phase 2 design document (`cuzk-phase2-design.md`, 791 lines) was written, covering the per-partition pipeline strategy, memory budget analysis, SRS manager design, and a 7-step implementation plan. The bellperson fork was created at `extern/bellperson/` with minimal changes (~130 lines): making `ProvingAssignment` and its fields public, exposing `synthesize_circuits_batch()`, and adding `prove_from_assignments()` for the GPU phase. The workspace was patched via `[patch.crates-io]`, and the fork compiles cleanly with all 8 existing tests passing, committed as `f258e8c7`. The themes of this chunk are: completing Phase 1's final deliverable (test data generation), rigorous analysis of upstream code before modification, minimal-fork philosophy (only exposing existing internal APIs rather than rewriting), and careful memory-aware design (the per-partition pipeline strategy reduces intermediate state from 136 GiB to 13.6 GiB). The project is now positioned to begin implementing the pipelined prover in cuzk-core, with the bellperson fork providing the necessary API surface.

The Two-Phase Pivot: Completing Phase 1 and Architecting Phase 2 of the cuzk Proving Engine 3254 words

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