Tracing the CuZK Engine: A Deep-Dive into the PSProve PoRep Failure

The Message

In this pivotal message (msg id=1641), the assistant reads a specific section of the Rust CuZK engine code:

[assistant] [read] /tmp/czk/extern/cuzk/cuzk-core/src/engine.rs
<path>/tmp/czk/extern/cuzk/cuzk-core/src/engine.rs</path>
<type>file</type>
<content>1525:                         let job_id = req.job_id.clone();
1526:                         let srs_mgr_clone = srs_mgr.clone();
1527:                         let param_cache_owned = param_cache_str.clone();
1528: 
1529:                         // 1. Parse SnapDeals input once (blocking) and load SRS
1530:                         let parse_result = tokio::task::spawn_blocking({
1531:                            ...

At first glance, this appears to be a routine file read—the assistant requesting lines 1525–1531 of a Rust source file. But in the context of the investigation unfolding across the preceding dozen messages, this read is a carefully targeted probe aimed at the heart of a production bug that had been blocking PoRep PSProve tasks from completing successfully through the CuZK proving engine.

The Investigation Context

To understand why this particular read matters, we must reconstruct the debugging journey that led here. The session had been investigating a baffling production failure: PoRep (Proof of Replication) tasks submitted through the PSProve pathway were failing with the error "porep failed to validate" when processed through the CuZK GPU proving engine. The failure was exquisitely specific—it only manifested when three conditions aligned simultaneously: the proof type was PoRep (not SnapDeals), the submission pathway was PSProve (the proof-share protocol used in the Filecoin market), and the proving backend was CuZK (the GPU-accelerated SNARK prover). Any two of these conditions worked fine. PoRep PSProve without CuZK succeeded. CuZK PoRep through the normal (non-PSProve) path succeeded. SnapDeals PSProve through CuZK succeeded. Only the triple intersection failed.

The user had already confirmed this diagnostic fingerprint in response to the assistant's earlier questions, ruling out general infrastructure problems, parameter file mismatches, and fundamental CuZK or PSProve bugs. The assistant had been systematically comparing the two code paths that feed data into CuZK: the normal path in cuzk_funcs.go (which worked) and the PSProve path in task_prove.go (which failed). Both paths constructed a SubmitProofRequest gRPC message with nearly identical fields—ProofKind, SectorSize, RegisteredProof, VanillaProof, SectorNumber, MinerId—but the source and construction of the VanillaProof bytes differed.

In the normal path, the C1 output (the output of SealCommitPhase1) was passed as raw Rust-generated JSON bytes from ffi.SealCommitPhase1(), wrapped in a C1OutputWrapper struct and base64-encoded. In the PSProve path, the C1 output had been deserialized from JSON into a Go struct (Commit1OutRaw) by the market client, then re-marshaled to JSON by the provider before being wrapped and base64-encoded. The critical question was whether this JSON round-trip introduced any subtle differences that the Rust CuZK engine would interpret differently.

Why This Read Was Made

The assistant had already traced through the Go-side plumbing in detail (messages 1636–1640), comparing the two paths line by line. It had discovered that the Rust CuZK prover in prover.rs ignores the registered_proof field from the gRPC request for PoRep proofs, instead using the value embedded inside the C1 JSON output itself. This ruled out a simple enum mapping mismatch. It had also examined the C1OutputWrapper struct definitions on both sides, noting that Go used int64 for SectorNum while Rust used u64—a type mismatch that was benign for positive sector numbers but worth noting.

The next logical step was to trace how the CuZK engine actually processes the vanilla_proof bytes once they arrive. The assistant had just finished examining the gRPC protobuf definition in message 1640, confirming that VanillaProof (singular, []byte) was the field used for PoRep, while VanillaProofs (plural, [][]byte) was used for SnapDeals and PoSt. Now it needed to see how the Rust engine deserializes and dispatches these bytes.

The read targets lines 1525–1531 of engine.rs—specifically the SnapDeals parsing section, as indicated by the comment "// 1. Parse SnapDeals input once (blocking) and load SRS". This is a deliberate comparative strategy: since SnapDeals PSProve works correctly through CuZK, understanding exactly how the SnapDeals path parses its input would reveal the expected pattern, against which the PoRep parsing path could be compared. The assistant was building a mental model of the engine's dispatch logic, looking for the branch point where PoRep and SnapDeals diverge, and where the PSProve path might be feeding subtly malformed data.

Input Knowledge Required

To fully understand this message, one needs knowledge spanning several domains. First, the architecture of the Filecoin proving pipeline: the two-phase commit protocol (SealCommitPhase1 produces a proof that SealCommitPhase2 wraps into a final SNARK), the distinction between PoRep and SnapDeals proof types, and the role of the PSProve protocol in the Filecoin market. Second, the CuZK system architecture: a gRPC-based GPU proving service where a Go client submits proof requests to a Rust backend that performs GPU-accelerated SNARK proving. Third, the serialization boundary between Go and Rust: the C1OutputWrapper struct that carries base64-encoded JSON between the two languages, and the serde_json deserialization that the Rust side performs. Fourth, the specific debugging methodology of comparative code-path analysis—tracing the same logical operation through two different implementations to find the divergence point.

The assistant also needed to understand the specific Rust codebase structure: that engine.rs contains the main event loop and dispatch logic for the CuZK proving service, that it handles multiple proof kinds (PoRep, SnapDeals, WinningPoSt, WindowPoSt) through a unified request/response protocol, and that the vanilla_proof field is parsed differently depending on the proof kind.

Assumptions and Their Validity

The assistant operated under several assumptions during this investigation. The primary assumption was that the bug was a plumbing issue—a mismatch in how data was packaged or interpreted between the Go client and the Rust engine—rather than a fundamental correctness issue in the CuZK prover itself. This assumption was well-supported by the evidence: the normal CuZK PoRep path worked, proving the CuZK engine could produce valid PoRep proofs given the right input. The PSProve path without CuZK worked, proving the PSProve infrastructure could produce valid proofs through the FFI. Only the combination failed, strongly suggesting a data-translation error at the Go/Rust boundary.

A secondary assumption was that the SnapDeals path, being known to work, could serve as a reference implementation. The assistant was implicitly assuming that the pattern of input parsing in the SnapDeals branch of engine.rs would mirror the PoRep branch, and that any deviation in the PSProve data would become visible when comparing how each branch deserializes its input.

A third assumption—one that would later prove partially incorrect—was that the JSON round-trip was functionally correct. The user had confirmed that the non-CuZK PSProve path worked, which meant the Go-re-marshaled JSON was valid enough for the FFI's SealCommitPhase2. But the assistant was beginning to suspect that "valid enough for the FFI" might not mean "identical to the original Rust JSON," and that the CuZK engine might be more sensitive to structural details like field ordering, whitespace, or the presence/absence of optional fields.

The Thinking Process Visible in This Message

This read reveals a methodical, hypothesis-driven debugging approach. The assistant is not randomly browsing the codebase—it is executing a targeted search, guided by a specific theory about where the bug might live. The progression across messages 1636–1641 shows a narrowing funnel: from comparing Go-side plumbing (the two computePoRep implementations), to examining the Rust-side data structures (C1OutputWrapper in prover.rs), to now tracing the engine dispatch logic that consumes these structures.

The choice to read the SnapDeals section specifically (rather than the PoRep section) is itself a reveal of the assistant's reasoning. By understanding how the working SnapDeals path parses its input, the assistant can establish a baseline of expected behavior. The next step—not yet taken in this message—would be to read the corresponding PoRep parsing section and compare the two. This comparative approach is a classic debugging technique: when one path works and another doesn't, the difference between them is almost certainly the bug.

The assistant is also building a cross-language mental model. It has already traced the data flow from Go structs through JSON serialization, through gRPC protobuf encoding, into Rust serde_json deserialization. Each read fills in another piece of this pipeline. The engine.rs read is particularly important because it's where the deserialized data actually gets used—where the vanilla_proof bytes are parsed into SealCommitPhase1Output and fed into the GPU proving pipeline.

Output Knowledge Created

This message produced a specific piece of knowledge: the exact structure of the SnapDeals input parsing code in the CuZK engine. The assistant now knows that at line 1529, the engine spawns a blocking task to parse SnapDeals input and load the SRS (Structured Reference String) parameters. This is a CPU-bound operation that is deliberately moved off the async event loop via tokio::task::spawn_blocking. The job_id, srs_mgr_clone, and param_cache_owned variables being cloned just before suggest these are captured for use inside the spawned block.

More importantly, this read establishes a reference point. The assistant can now compare this SnapDeals parsing code against the PoRep parsing code elsewhere in engine.rs. If the PoRep parsing code follows a different pattern—perhaps expecting different JSON structure, or using a different deserialization strategy—that difference could explain why the Go-re-marshaled JSON works for SnapDeals but fails for PoRep.

The read also implicitly confirms that the engine uses a unified request format where vanilla_proof (singular) contains different JSON structures depending on the proof kind. For SnapDeals, it contains a SnapDealProofInput structure. For PoRep, it contains a C1OutputWrapper wrapping a SealCommitPhase1Output. The engine must branch on ProofKind to deserialize appropriately. If the PSProve path is sending data that is structurally valid as JSON but doesn't match what the PoRep branch expects, the deserialization could silently produce incorrect values.

Significance Within the Larger Investigation

This message represents a turning point in the investigation. The assistant has moved from the Go client code (where the data originates) to the Rust engine code (where the data is consumed). The next logical step—comparing the PoRep and SnapDeals parsing branches in engine.rs—would either confirm the JSON round-trip hypothesis or force the assistant to develop a new theory.

The investigation would eventually identify a SectorNum type mismatch (int64 vs u64) and a structural difference in how the PSProve path constructs its wrapper compared to the shared wrapC1Output function. But at this moment, captured in message 1641, the assistant is still gathering evidence, methodically working through the codebase with the disciplined patience of a debugger who knows that the bug is somewhere in the plumbing and that careful comparison will eventually reveal it.