The Moment of Truth: Launching the First Real Proof Through the cuzk Daemon

Introduction

In the lifecycle of any infrastructure project, there is a single moment that separates months of design and implementation from the cold reality of production: the first end-to-end test with real data on real hardware. For the cuzk proving engine — a pipelined SNARK proving daemon designed to replace Curio's ad-hoc C2 proof generation for Filecoin PoRep — that moment arrived in message <msg id=218>. This message represents the critical transition from "it compiles and the pipeline works" to "it produces real proofs with measurable performance characteristics." It is the culmination of five segments of deep investigation, architecture design, and implementation, and it reveals the assistant's methodical approach to validating complex systems.

Context: What Led to This Message

The cuzk project had been under development across multiple sessions. By segment 4, the assistant had implemented Phase 0 of the proving engine: a Rust workspace with six crates, a gRPC API, a core engine with priority scheduler, and wiring to filecoin-proofs-api for actual Groth16 proof generation. The workspace compiled cleanly. The parameter cache was populated with 29 files totaling 32 GiB of SRS parameters. A 51 MB C1 test output was ready. The hardware was an RTX 5070 Ti (Blackwell architecture, compute capability 12.0) with 16 GB VRAM.

But there was a gnawing uncertainty. The CUDA backend — supraseal-c2 — delegates to sppark, which uses nvcc for JIT compilation. The question was whether nvcc with CUDA 13.1 could target Blackwell (sm_120). The assistant had spent messages <msg id=197> through <msg id=217> tracing through build scripts, checking rust-gpu-tools for compute capability filtering, and verifying that sppark's build system doesn't explicitly filter architectures. The conclusion was optimistic but untested: nvcc should handle it.

The Core Reasoning of Message 218

The message opens with a careful analysis of the parameter cache initialization path. This is not casual reasoning — it is a forensic examination of the storage-proofs-core settings system. The assistant had discovered in <msg id=217> that SETTINGS is a lazy_static initialized from Environment::with_prefix("FIL_PROOFS"). The critical insight is that FIL_PROOFS_PARAMETER_CACHE env var maps to the parameter_cache field in the settings struct. But there is a subtle timing dependency: if any code accesses SETTINGS before the engine sets the env var, the lazy initialization would capture the default path (/var/tmp/filecoin-proof-parameters/) instead of the intended /data/zk/params.

The assistant's reasoning here is meticulous. It traces through the code to confirm that the engine sets the env var before calling seal_commit_phase2, which is the first point where SETTINGS would be accessed. The lazy_static guarantees that initialization is deferred until first access, so as long as the env var is set before that call, the correct path is captured. This is a correct analysis, but it makes an implicit assumption: that no other code path during daemon startup touches SETTINGS. If, for example, the gRPC server initialization or configuration loading triggered a parameter cache lookup, the env var might not yet be set. The assistant does not explicitly verify this negative — it trusts the code structure.

The Decision to Start the Daemon

Having satisfied itself that the env var mechanism would work, the assistant makes a pragmatic decision: start the daemon with FIL_PROOFS_PARAMETER_CACHE=/data/zk/params explicitly set in the environment, in addition to the engine's internal set_var. This is a belt-and-suspenders approach. The command uses nohup and redirects output to a log file, which is standard practice for long-running processes. The choice of TCP mode (--listen 0.0.0.0:9820) over Unix Domain Sockets is explicitly noted as "for simplicity" — UDS would be the production choice for local communication, but TCP is easier to debug and doesn't require socket file permissions.

The assistant then verifies the daemon started correctly by checking the log output. The log shows four INFO messages in quick succession: daemon starting, configuration loaded, engine starting, engine started. This confirms the initialization path is clean. But there is a notable absence: the daemon does not print any GPU detection or CUDA initialization messages at startup. This is because GPU initialization in filecoin-proofs-api is lazy — it only happens when the first proof is submitted. The assistant does not comment on this, but it is a reasonable design choice that avoids holding GPU resources when idle.

Assumptions and Potential Pitfalls

Several assumptions underpin this message, some explicit and some implicit:

Explicit assumption: The lazy_static initialization of SETTINGS will capture the env var because the engine sets it before the first proof call. This is correct based on the code, but it assumes no other code path triggers SETTINGS access during daemon startup. In practice, the daemon's initialization sequence is: load config → start engine → start gRPC server → wait for requests. None of these steps should touch SETTINGS, but if any library initialization in the dependency chain referenced the parameter cache, the env var would be missed.

Implicit assumption: The CUDA 13.1 toolchain can JIT-compile sppark kernels for Blackwell (sm_120). The assistant had checked that sppark's build.rs doesn't filter architectures, but this is a runtime concern — the fatbin might not contain sm_120 code, and nvcc's JIT compiler might or might not support it. The assistant is essentially trusting NVIDIA's backward compatibility promise.

Implicit assumption: The 51 MB C1 JSON file is a valid PoRep C1 output for a 32 GiB sector. The assistant had verified the file exists and is non-empty, but had not validated its internal structure beyond what the deserialization code would do. If the file were malformed or from a different sector size, the error would only surface during proof generation.

Implicit assumption: The daemon has sufficient memory. The SRS parameters are 45 GiB, and the synthesis phase requires additional working memory. The machine has 256+ GiB of RAM based on earlier checks, but the assistant does not explicitly verify this before starting.

Input Knowledge Required

To understand this message, the reader needs knowledge of:

  1. Filecoin's proof architecture: PoRep (Proof of Replication) has two phases — C1 (commit phase 1, which produces a compressed circuit representation) and C2 (commit phase 2, which runs the Groth16 prover). C2 is the computationally expensive part, requiring ~200 GiB peak memory and GPU acceleration.
  2. The storage-proofs-core settings system: The SETTINGS lazy_static and its Environment-based configuration. The FIL_PROOFS prefix convention means env vars like FIL_PROOFS_PARAMETER_CACHE map to struct fields with the suffix as the field name (e.g., parameter_cache).
  3. The cuzk architecture: The daemon has an engine that manages a priority queue, GPU workers that call filecoin-proofs-api, and an SRS manager that keeps parameters in memory across proofs. The SRS residency benefit (avoiding reloading 45 GiB from disk) is the key performance advantage.
  4. Groth16 proving pipeline: The phases are: deserialize C1 output → load SRS parameters → synthesize circuit (CPU-bound, massively parallel) → run NTT/MSM on GPU → produce and verify proof.

Output Knowledge Created

This message produces several concrete outputs:

  1. A validated daemon startup: The daemon is confirmed running on TCP port 9820, responsive, and ready to accept proof submissions.
  2. A confirmed env var mechanism: The FIL_PROOFS_PARAMETER_CACHE env var correctly overrides the default parameter cache path. This is verified by the daemon's log output showing it loaded configuration with the custom listen address.
  3. A baseline for performance measurement: The daemon's uptime and zero-proof state provide a clean baseline. The first proof will measure SRS load time (~15 seconds from disk) and total prove time, while the second proof will isolate the SRS residency benefit.
  4. Confidence in the CUDA backend: The daemon started without CUDA errors, which is the first indication that the cuda-supraseal build works on Blackwell hardware.

The Thinking Process

The assistant's thinking in this message is structured as a risk assessment followed by a controlled experiment. The first paragraph is pure analysis — tracing the env var → SETTINGS → parameter_cache chain and verifying the timing dependency. This is characteristic of the assistant's approach throughout the session: never assume, always verify by reading source code.

The transition from analysis to action is marked by "Now let me start the daemon and run a real proof." This is a conscious shift from investigation to execution. The assistant chooses TCP mode explicitly, documents the choice, and verifies the daemon started correctly before proceeding.

The log output is presented without commentary — the assistant trusts the reader (or its own future self) to interpret the standard INFO messages. This is efficient but assumes familiarity with the codebase's logging conventions.

Significance in the Larger Narrative

Message <msg id=218> is the inflection point of Segment 5. Everything before it was preparation: building, checking parameters, verifying test data. Everything after it is validation: the first proof completes in 116.8 seconds, the second in 92.8 seconds (a 20.5% improvement from SRS residency), and both proofs pass internal verification. The daemon correctly tracks metrics, queue depth, and proof counts.

The message also sets the stage for the hardening work that follows in the rest of Segment 5. Once the assistant knows the pipeline works, it can add tracing spans, timing breakdowns, Prometheus counters, GPU detection, and graceful shutdown — all the observability improvements that make Phase 1 development tractable. Without this validation, those improvements would be premature optimization.

Conclusion

Message <msg id=218> is a masterclass in methodical system validation. The assistant combines source code analysis (tracing the env var mechanism), risk assessment (identifying the lazy_static timing dependency), and pragmatic execution (starting the daemon with redundant env var settings). It makes reasonable assumptions about CUDA compatibility and memory availability, documents its choices, and verifies the immediate outcome before proceeding. The message is both the conclusion of Phase 0 implementation and the foundation for all subsequent performance measurement and hardening work. It transforms cuzk from a design into a running system that produces real, verifiable Groth16 proofs.