Tracing the PoRep PSProve Bug: A Cross-Language Debugging Pivot at the CuZK Boundary

Introduction

In the course of a deep investigation into a production bug where PoRep (Proof of Replication) PSProve tasks fail when processed through the CuZK proving engine, message [msg 1624] marks a critical inflection point. After meticulously tracing through Go struct serialization, JSON round-trip fidelity, and Rust FFI boundaries, the assistant pivots from examining data formatting issues to investigating how the CuZK Rust daemon selects proving parameters based on proof type. This message captures the moment when a debugging hypothesis is tested against the actual architecture of the cross-language proving pipeline, revealing important structural details about the CuZK server's API design.

The bug under investigation is specific and puzzling: PoRep PSProve tasks fail with "porep failed to validate" when processed through CuZK, while Snap PSProve tasks work correctly, and normal (non-PSProve) PoRep C2 tasks also work correctly through CuZK. This narrow failure mode—isolated to the intersection of PSProve and CuZK for PoRep—suggests a plumbing issue at the boundary between these two systems rather than a fundamental problem with either one alone.

The Message in Full

The subject message contains the assistant's reasoning and a grep command:

There's only one POREP_SEAL_COMMIT kind — no distinction between interactive/synthetic/NiPoRep in cuzk's API. The RegisteredProof field is passed as a number. Let me check if the cuzk Rust daemon uses this to select the right groth16 parameters:

>

``` [grep] registered_proof|RegisteredProof|proof_type|proof_kind.POREP|POREP.seal Found 313 matches (showing first 100) /tmp/czk/extern/cuzk/cuzk-server/src/service.rs: Line 41: registered_proof: req.registered_proof,

>

/tmp/czk/extern/cuzk/cuzk-bench/src/gen_vanilla.rs: Line 158: registered_proof: u64, Line 167: let post_proof_type = registered_post_proof_from_u64(registered_proof) Line 173: "Generating WinningPoSt vanilla proofs (proof_type={:?}, sector={}, miner={})", Line 174: post_proof_type, sector_number, miner_id Line 182: ... ```

The assistant's reasoning reveals a key architectural insight: the CuZK protobuf API defines only a single POREP_SEAL_COMMIT proof kind, with no sub-distinction for interactive, synthetic, or NiPoRep (Non-Interactive PoRep) variants. The specific proof type—which determines which Groth16 verification circuit and proving parameters to use—is carried solely through the numeric RegisteredProof field.

The Debugging Journey: How We Got Here

To understand why message [msg 1624] represents a pivotal moment, we must trace the investigation that preceded it. The assistant had been methodically comparing two code paths: the normal PoRep C2 path in cuzk_funcs.go and the PSProve PoRep path in task_prove.go.

The initial hypothesis centered on a JSON serialization round-trip issue ([msg 1611]). In the normal path, the vanilla proof bytes from ffi.SealCommitPhase1() are passed directly to CuZK without intermediate Go struct deserialization. In the PSProve path, the Commit1OutRaw struct is unmarshaled from JSON (when the client uploads the proof data), then re-marshaled back to JSON before being wrapped and sent to CuZK. The concern was that this round-trip through Go structs might produce JSON that differs from the original Rust output, causing CuZK's Rust-based deserialization to fail.

The assistant dug deep into the type system, examining PoseidonDomain, Sha256Domain, and HasherDomain types (<msg id=1613-1615>), discovering that HasherDomain = any causes the custom MarshalJSON methods on domain types to be bypassed when values are deserialized from JSON. The assistant also confirmed through a subagent task ([msg 1622]) that Rust's Commitment type ([u8; 32]) serializes as a JSON array of 32 integers, while Go's [32]byte serializes as base64 by default.

However, a test in porep_vproof_test.go ([msg 1623]) confirmed that the JSON round-trip does work correctly when compared at the map[string]interface{} level. This ruled out the serialization hypothesis, forcing the assistant to look elsewhere for the root cause.

The Pivot: From Serialization to Proof Type Selection

Message [msg 1624] represents the moment when the assistant pivots from the serialization hypothesis to a new line of inquiry: does CuZK correctly handle different PoRep proof types? The reasoning is subtle but important.

The assistant had previously noted ([msg 1623]) that the error &#34;porep failed to validate&#34; means the SNARK proof was generated successfully (no error from CuZK or SealCommitPhase2) but failed verification via ffi.VerifySeal(). This is a critical distinction: CuZK produced a proof, but that proof was invalid. This points not to a data corruption issue but to a parameter mismatch—CuZK might be using the wrong proving circuit or verification parameters for the proof type.

The assistant's observation that "there's only one POREP_SEAL_COMMIT kind" in CuZK's API is the key insight. If CuZK's protobuf API doesn't distinguish between different PoRep variants at the message level, then the RegisteredProof numeric field is the only mechanism for selecting the correct proving parameters. If this field is incorrectly set, or if CuZK's Rust daemon ignores it for PoRep (using a hardcoded default instead), the wrong proving circuit would be used, producing an invalid proof.

The grep results reveal that registered_proof is indeed received in service.rs line 41 (registered_proof: req.registered_proof), confirming the field is available. But the assistant's question—"does the cuzk Rust daemon use this to select the right groth16 parameters?"—remains unanswered in this message. The grep also shows cuzk-bench/src/gen_vanilla.rs using registered_post_proof_from_u64() for PoSt proofs, suggesting a pattern where numeric proof type values are mapped to specific proving parameters.

Input Knowledge Required

To fully understand this message, the reader needs several pieces of contextual knowledge:

  1. The Filecoin proof hierarchy: PoRep (Proof of Replication) is distinct from PoSt (Proof of Spacetime), and within PoRep there are variants like interactive PoRep (StackedDrg), NiPoRep (Non-Interactive), and synthetic PoRep. Each variant uses different circuits and proving parameters.
  2. The PSProve architecture: PSProve is a proof-sharing system where clients generate Phase1 vanilla proofs and upload them to a market, and providers download these proofs to compute Phase2 SNARK proofs. This introduces a JSON round-trip through Go structs that doesn't exist in the normal proving path.
  3. CuZK's role: CuZK is a GPU-accelerated proving service that replaces the CPU-based SealCommitPhase2. It accepts a protobuf request containing the vanilla proof bytes and proof type, runs the Groth16 prover on GPU, and returns the SNARK proof.
  4. The Go/Rust boundary: The proving pipeline crosses language boundaries multiple times—Go calls Rust FFI for SealCommitPhase1, serializes/deserializes JSON in Go, then sends protobuf messages to a Rust gRPC server (CuZK). Each boundary is a potential source of data transformation errors.
  5. The RegisteredProof enum: This numeric enum (e.g., StackedDrg32GiBV1_1 = 8, StackedDrg32GiBV1_2_Feat_NiPoRep = 18) encodes both the sector size and the proof variant. It must be consistent across all stages of proving and verification.

Output Knowledge Created

This message produces several important outputs:

  1. Confirmation that CuZK's API is monolithic for PoRep: The protobuf defines only one POREP_SEAL_COMMIT kind, meaning all PoRep variants (interactive, NiPoRep, synthetic) flow through the same API endpoint. Variant selection is delegated entirely to the numeric RegisteredProof field.
  2. Evidence that registered_proof is received by the CuZK server: The grep hit in service.rs line 41 confirms the field is extracted from the protobuf request, making it available for parameter selection.
  3. A new hypothesis to investigate: If CuZK ignores the RegisteredProof field for PoRep (perhaps using a hardcoded default), or if the PSProve path sends a different proof type than the normal path, that would explain why only the PSProve+CuZK combination fails.
  4. A direction for further investigation: The assistant must now examine how CuZK's Rust pipeline uses the registered_proof value—specifically in pipeline.rs and engine.rs—to determine if parameter selection is correct.

The Thinking Process

The assistant's reasoning in this message demonstrates a methodical debugging approach characteristic of cross-language protocol investigations. The thought process follows a clear arc:

First, the assistant establishes the current state of knowledge: the JSON round-trip hypothesis has been ruled out by the passing test. This eliminates data corruption as the likely cause.

Second, the assistant re-examines the error mode: CuZK produces a proof, but it doesn't verify. This shifts the focus from "is the data intact?" to "are the parameters correct?" A proof that fails verification despite being well-formed suggests the prover used the wrong circuit or parameters.

Third, the assistant examines CuZK's API surface to understand how proof types are communicated. The discovery that there's only one POREP_SEAL_COMMIT kind is significant—it means CuZK doesn't have separate endpoints or message types for different PoRep variants. The RegisteredProof numeric field is the sole carrier of variant information.

Fourth, the assistant formulates the next question: does CuZK's Rust daemon actually use this field to select Groth16 parameters? The grep confirms the field is received, but the critical code path (how it's used in the proving pipeline) hasn't been examined yet.

This thinking process reveals a sophisticated debugging strategy: rule out simple explanations first (data corruption), then examine the architecture at the boundary where the failure occurs (CuZK's API), and finally trace the specific parameter flow through the system. The assistant is systematically narrowing the search space, moving from high-level data flow to low-level parameter selection.

Broader Implications

Message [msg 1624] illustrates a fundamental challenge in cross-language proving systems: type information can be lost or transformed at language boundaries. In a pure Rust proving pipeline, the RegisteredProof enum would be a strongly-typed value carried through the entire flow. But in this Go→protobuf→Rust pipeline, the enum becomes a bare uint64 at the protobuf boundary, and it's up to each side to interpret it correctly. If the Go side sends a different value than expected, or if the Rust side ignores the value and uses a default, the proof will fail.

This message also demonstrates the value of architecture-level reasoning in debugging. Rather than adding more logging or trial-and-error fixes, the assistant uses knowledge of the system's architecture to formulate targeted questions about data flow at specific boundaries. This approach is especially valuable in distributed proving systems where the failure may occur far from its root cause.

The investigation continues beyond this message, but message [msg 1624] captures the critical moment when the debugging lens shifts from "how is the data serialized?" to "how are the proving parameters selected?"—a pivot that ultimately leads to the root cause of the production bug.