The Moment of Proof: Validating the cuzk Proving Pipeline End-to-End

A TODO List That Marks a Milestone

On its surface, message [msg 232] in the cuzk development session is unremarkable: a structured TODO list update, serialized as JSON, marking several items as completed. But this message represents a watershed moment in the construction of a distributed SNARK proving daemon for Filecoin. It is the formal acknowledgment that Phase 0 of the cuzk project — the scaffold phase — has achieved its primary goal: producing a real, valid Groth16 proof through a custom gRPC-based proving pipeline, on real hardware, with measurable performance characteristics.

The message reads:

[
  {
    "content": "Verify cuzk workspace builds clean (no-default-features)",
    "status": "completed",
    "priority": "high"
  },
  {
    "content": "Build with CUDA features for GPU proving",
    "status": "completed",
    "priority": "high"
  },
  {
    "content": "Run daemon with FIL_PROOFS_PARAMETER_CACHE=/data/zk/params and test real PoRep C2 proof",
    "status": "completed",
    "priority": "high"
  },
  {
    "content": "Measure SRS residency benefit (first vs second proof)",
    "status": "in_progress",
    "priority": "high"
  }
]

This short JSON payload is the culmination of hours of debugging, code reading, build system wrangling, and patient monitoring of a computation that consumed over 200 GiB of memory and 14,000% CPU utilization across more than a hundred cores. To understand why this message matters, we must understand the journey that led to it.

Context: The cuzk Proving Engine

The cuzk project (a portmanteau of "CUDA" and "zk") is an ambitious effort to build a persistent, pipelined SNARK proving daemon for Filecoin's Proof-of-Replication (PoRep) protocol. Prior work in this session (segments 0–4) had produced five optimization proposals analyzing the existing supraseal-c2 pipeline, identified nine structural bottlenecks including a ~200 GiB peak memory footprint, and designed a new architecture centered on a gRPC-based daemon with a priority scheduler, SRS memory residency, and multi-GPU support.

Phase 0, implemented in segment 4, created the Rust workspace with six crates, defined the gRPC protobuf API, implemented the core engine with a priority scheduler, wired the prover module to filecoin-proofs-api calls, and resolved numerous build system incompatibilities. But until message [msg 232], the pipeline had never been tested with a real proof on real GPU hardware. It was a skeleton waiting for its first breath.

The Validation Run

The events leading to message [msg 232] began with a release build using --features cuda-supraseal on a machine equipped with an NVIDIA RTX 5070 Ti (Blackwell architecture, CUDA 13.1). The assistant started the daemon with the FIL_PROOFS_PARAMETER_CACHE environment variable pointing to /data/zk/params, where the 32 GiB PoRep parameters had been previously staged (see [msg 218]).

A 51 MB C1 output — the intermediate representation from the first phase of PoRep sealing — was submitted via gRPC using the cuzk-bench single command. What followed was a tense wait as the daemon:

  1. Deserialized the outer JSON envelope and base64-decoded the inner C1 structure
  2. Registered the proof type as StackedDrg32GiBV1_1 — the correct circuit identifier for 32 GiB sectors
  3. Missed the SRS memory cache (first call) and began loading a 45 GiB parameter file from disk
  4. Loaded the parameters into the SupraSeal GPU backend in approximately 15 seconds
  5. Entered the CPU-bound circuit synthesis phase, building ~130 million constraints The assistant monitored progress through a series of status checks. At one point, ps reported the daemon using 14,253% CPU — roughly 142 cores working in parallel on constraint generation — and 203 GiB of RSS (resident memory), confirming the memory model derived in the earlier optimization proposals ([msg 227]). After 116.8 seconds, the proof completed. It was 1,920 bytes — exactly the expected size for a Groth16 proof over BLS12-381. Internal verification passed. The daemon correctly incremented its proof counter and recorded the metrics.

Why This Message Was Written

Message [msg 232] was written to formalize this validation and to reorient the development effort toward the next objective. The assistant's TODO tool provides structured task tracking, and updating it serves several purposes:

First, it marks a critical risk closure. Until a real proof was produced, the entire cuzk architecture was theoretical. The gRPC protocol might have had bugs. The prover wiring might have failed to pass parameters correctly. The GPU backend might not have initialized. The SRS parameter loading might have failed silently. Every one of these failure modes was eliminated by this single run.

Second, it establishes a performance baseline. The 116.8 second end-to-end time — including ~15 seconds for SRS loading — gives a concrete starting point for optimization. The SRS residency benefit, measured in the subsequent proof at 92.8 seconds (a 20.5% improvement), validates the core architectural decision to keep parameters pinned in GPU memory across proof submissions.

Third, it creates accountability for the next phase. By marking the SRS residency measurement as "in_progress" rather than "completed," the assistant signals that more work remains — specifically, running a second proof to quantify the benefit, which was already underway when this message was written.

Assumptions and Their Validation

The message implicitly confirms several assumptions that underpinned the Phase 0 design:

Input Knowledge Required

To fully understand this message, one needs to understand:

Output Knowledge Created

This message, combined with the validation run it documents, creates several forms of knowledge:

  1. Empirical proof that the cuzk Phase 0 pipeline works end-to-end. The architecture is not just a design document; it is a running system that produces valid proofs.
  2. A performance baseline for 32 GiB PoRep C2 proving on an RTX 5070 Ti: 116.8 seconds first proof (cold SRS), 92.8 seconds subsequent proofs (warm SRS). This is the first data point for this specific GPU architecture in this pipeline.
  3. Quantification of the SRS residency benefit: 20.5% speedup from keeping parameters in memory. This validates the Persistent Prover Daemon optimization proposed in earlier work ([chunk 0.0]).
  4. Confirmation of the memory model: The observed 203 GiB RSS matches the ~200 GiB peak memory footprint identified in the background reference document. The synthesis phase is confirmed as the dominant memory consumer.
  5. A validated test harness: The cuzk-bench single command, the gRPC protocol, and the daemon's metrics tracking all proved correct under real load.

The Thinking Process Behind the Message

The assistant's reasoning is visible in the sequence of actions leading to this message. After the proof completed ([msg 230]), the assistant immediately checked the bench client output and daemon status ([msg 231]), confirming the proof counter incremented to 1. Only then was the TODO list updated.

The truncation in the message — the "..." at the end of the fourth TODO item — reveals that the assistant was already looking ahead. The SRS residency measurement was in progress, and the assistant's attention was shifting from "does it work?" to "how well does it work?" This forward-looking posture is characteristic of the entire cuzk development effort: each milestone is immediately followed by instrumentation and measurement to inform the next phase.

Conclusion

Message [msg 232] is a TODO list update that marks the transition from "it compiles" to "it proves." It is the formal acknowledgment that the cuzk proving engine has crossed the most critical threshold in any software project: producing correct output on real hardware. The 1,920-byte Groth16 proof that triggered this update represents the successful integration of Rust async gRPC servers, C++ GPU kernels, Filecoin's proof API, and a custom priority scheduler — a remarkable feat of systems engineering that the TODO list, in its understated JSON format, quietly celebrates.