The Byte-Level Divergence: Tracing a PSProve PoRep Failure Through JSON Serialization

Introduction

In the intricate world of Filecoin proof generation, where correctness depends on byte-perfect alignment across Go, C, and Rust codebases, the most elusive bugs are often those that hide in plain sight. Message 1671 of this coding session captures a pivotal moment in a deep investigation of a PSProve PoRep CuZK failure—a moment where the assistant deliberately abandons the systematic code-tracing approach that has consumed the preceding hours and adopts a radically different strategy: thinking about the problem at the byte level, where the actual data diverges between a working path and a failing one.

This message is a turning point. It represents the shift from exhaustive structural verification (enum mappings, struct field comparisons, data flow analysis) to a more creative, hypothesis-driven investigation. The assistant has confirmed that every enum mapping matches, every struct field aligns, every data transformation preserves semantic content. Yet the proof still fails. The only remaining variable is the raw byte content of the JSON payload itself—and the assistant now confronts this directly.

The Context of the Investigation

To understand the significance of message 1671, we must first understand the problem it addresses. The CuZK proving engine supports GPU-accelerated proof generation for Filecoin's Proof-of-Replication (PoRep) protocol. Two paths exist for generating the Commit Phase 2 (C2) SNARK proof:

  1. The normal cuzk path (implemented in cuzk_funcs.go): Takes the raw output bytes from ffi.SealCommitPhase1(), wraps them in a JSON envelope, and sends them to the CuZK GPU prover. This path works correctly.
  2. The PSProve cuzk path (implemented in task_prove.go): Takes a Commit1OutRaw Go struct that has been deserialized from JSON, re-serializes it with json.Marshal(), wraps it in the same envelope, and sends it to CuZK. This path fails—CuZK successfully generates a SNARK, but the subsequent ffi.VerifySeal() call in Go rejects it as invalid. The PSProve path is used for "proving service" workloads, where proof requests arrive as JSON over the network and must be processed by the GPU proving infrastructure. The fact that CuZK can generate a SNARK from the re-serialized JSON but that SNARK fails verification is deeply puzzling. If the JSON contained semantically correct data, the SNARK should verify. If the JSON contained corrupted data, CuZK should either reject it or produce a SNARK that matches the corrupted data—but verification uses the original in-memory values, which would then mismatch. The investigation has been exhaustive. The assistant has traced RegisteredSealProof enum mappings across Go, C, and Rust, finding them identical. It has compared JSON struct fields between Go's Commit1OutRaw and Rust's SealCommitPhase1Output, confirming every field matches. It has verified the make_prover_id function against Go's toProverID, confirming LEB128/varint encoding parity. It has analyzed the data flow through the proofshare system and confirmed no corruption occurs in transit. Everything checks out—yet the bug persists.

The Message: A Shift in Strategy

Message 1671 opens with the assistant dismissing a potential lead:

This is very interesting but probably not the root cause — the local bellperson fork is the same fork used for all cuzk PoRep proofs, including the working normal path. So if the fork caused issues, ALL cuzk proofs would fail, not just PSProve ones.

This dismissal is crucial. It demonstrates the assistant's commitment to logical consistency: if a dependency version mismatch were the cause, it would manifest universally, not selectively. The PSProve-only failure pattern demands a PSProve-specific explanation.

The assistant then announces its strategic pivot:

Let me take a completely different approach. Instead of tracing code, let me think about what's actually different about the failing case at the byte level:

This is the core of the message. The assistant identifies the fundamental difference between the two paths:

Working normal cuzk path (cuzk_funcs.go):

vproof = ffi.SealCommitPhase1() output → raw Rust JSON bytes
wrapped = wrapC1Output(vproof, sectorNum, sectorSize)

Failing PSProve cuzk path (task_prove.go):

request = *Commit1OutRaw (Go struct, deserialized from JSON)
vproof = json.Marshal(request) → Go-serialized JSON bytes
wrapped = json.Marshal(c1OutputWrapper{SectorNum, Phase1Out: vproof, SectorSize})

The insight is elegant: in the normal path, vproof contains the exact bytes that Rust's serde_json originally produced during SealCommitPhase1. In the PSProve path, vproof contains Go's re-serialization of the same data after a round-trip through json.Unmarshal and json.Marshal. While the semantic content is identical, the byte representation may differ in subtle ways—field ordering, whitespace, number encoding, or binary data representation.

The Field Ordering Hypothesis

The assistant immediately considers field ordering as a potential source of divergence:

For Commit1OutRaw, Go's field order is: comm_d, comm_r, registered_proof, replica_id, seed, ticket, vanilla_proofs For Rust's SealCommitPhase1Output, field order is: registered_proof, vanilla_proofs, comm_r, comm_d, replica_id, seed, ticket

>

But serde_json handles field order-independent deserialization, so this shouldn't matter...

This reasoning is correct. JSON parsers, by specification, treat objects as unordered sets of key-value pairs. Both Go's encoding/json and Rust's serde_json are compliant parsers that ignore field ordering. The assistant correctly dismisses this hypothesis but demonstrates thoroughness by considering it.

The VanillaProofs Map Key Investigation

Having dismissed field ordering, the assistant pivots to a more subtle possibility: the vanilla_proofs map key. The VanillaSealProof enum in Rust has only five variants:

StackedDrg2KiBV1(...)
StackedDrg8MiBV1(...)
StackedDrg512MiBV1(...)
StackedDrg32GiBV1(...)
StackedDrg64GiBV1(...)

All variants are "V1" regardless of the actual RegisteredSealProof being used. A proof registered as StackedDrg32GiBV1_1_Feat_SyntheticPoRep would still serialize its vanilla proofs under the key "StackedDrg32GiBV1". The assistant wonders whether this mismatch between the registered_proof field value and the vanilla_proofs map key could cause issues during Go's round-trip serialization.

The assistant launches a task to investigate:

But what if there's an issue with the PoW path specifically? The powsrv uses StackedDrg32GiBV1_1 as spt. What key does the Rust VanillaSealProof enum produce for this registered proof? Let me check:

This task is designed to verify that the JSON key in vanilla_proofs always uses the base V1 variant name, regardless of which RegisteredSealProof was used. The assistant correctly anticipates the answer: yes, the key is always the base V1 name, and the round-trip through Go is safe because Go preserves the string key as-is.

The Thinking Process: Methodical Creativity

What makes message 1671 remarkable is the thinking process it reveals. The assistant has been operating in a highly systematic mode—tracing enums, comparing structs, analyzing data flows. This is the default mode for debugging cross-language serialization issues: verify that every structural element matches, and the bug will reveal itself.

But the assistant recognizes that this approach has reached its limit. All structural elements match. The bug persists. The only remaining degree of freedom is the actual byte content of the JSON payload—something that structural analysis cannot fully capture because it depends on the specific serialization behavior of each language's JSON library.

The shift to byte-level thinking is a creative leap. It requires the assistant to recognize that two semantically identical JSON documents can produce different verification outcomes if they differ in byte-level representation—not because the parser misinterprets them, but because the verification algorithm uses the raw bytes directly rather than the parsed values.

This is a subtle but crucial insight. The SNARK verification process doesn't just use the parsed values from the JSON; it uses the raw bytes in specific ways. If the replica_id is computed as hash(prover_id, sector_id, ticket, comm_d), and any of these values differ between the SNARK generation side (which uses the re-serialized JSON) and the verification side (which uses the original in-memory values), the proof will fail.

Assumptions and Their Validity

The message reveals several assumptions the assistant is making:

  1. The bellperson fork is not the cause: The assistant assumes that because the same fork is used for both working and failing paths, it cannot be the selective cause. This is logically sound.
  2. Field ordering doesn't matter: The assistant correctly assumes that JSON parsers are field-order-independent. This is a safe assumption for standard-compliant parsers.
  3. The vanilla_proofs map key is consistent: The assistant assumes that the JSON key in vanilla_proofs always uses the base V1 variant name. The launched task will confirm this.
  4. Go's json.Marshal produces semantically equivalent output: The assistant assumes that the Go re-serialization preserves all values correctly. This is the central hypothesis being tested. The most significant assumption—and the one that may prove incorrect—is that the byte-level difference between Rust's original JSON and Go's re-serialized JSON is the root cause. If this assumption is wrong, the assistant will need to look elsewhere, perhaps at the CuZK gRPC layer or the wrapper format itself.

Input Knowledge Required

To fully understand message 1671, one needs:

  1. Knowledge of the codebase structure: Understanding that cuzk_funcs.go implements the normal CuZK path and task_prove.go implements the PSProve path, and how they differ in data flow.
  2. Understanding of JSON serialization in Go and Rust: How json.Marshal in Go differs from serde_json::to_vec in Rust in terms of field ordering, number encoding, and binary data representation.
  3. Knowledge of the Filecoin proof pipeline: Understanding SealCommitPhase1, SealCommitPhase2, the Commit1OutRaw struct, and how the SNARK proof is verified.
  4. Awareness of the CuZK architecture: How the GPU prover receives data via gRPC, deserializes the wrapper JSON, decodes base64, and passes the inner JSON to seal_commit_phase2.
  5. Understanding of the VanillaSealProof enum: Its variants, how they map to RegisteredSealProof, and how they serialize to JSON keys.

Output Knowledge Created

Message 1671 creates several important pieces of knowledge:

  1. The byte-level divergence hypothesis: The recognition that the fundamental difference between working and failing paths is whether the JSON bytes originate from Rust or from Go's re-serialization.
  2. The field ordering dismissal: A documented conclusion that field ordering differences between Go and Rust JSON serialization are not the cause, because JSON parsers are field-order-independent.
  3. The vanilla_proofs map key question: An identified area of investigation—whether the mismatch between registered_proof values (which may include feature suffixes like Feat_SyntheticPoRep) and vanilla_proofs map keys (which always use base V1 names) could cause issues during round-trip serialization.
  4. A methodological contribution: The demonstration that when systematic structural analysis exhausts its utility, a shift to byte-level thinking can open new investigative avenues.

The Broader Significance

Message 1671 is not just about debugging a specific proof failure. It illustrates a general principle of cross-language systems debugging: structural parity does not guarantee behavioral parity. Two systems can agree on every enum value, every struct field, every data transformation, and still produce incompatible outputs because of subtle differences in serialization behavior.

The assistant's willingness to abandon a systematic approach that has consumed hours of work and adopt a fundamentally different strategy is a mark of intellectual flexibility. Many debugging sessions fail because the investigator becomes attached to their current approach, continuing to refine it even after it has stopped producing results. The assistant recognizes the diminishing returns of structural analysis and pivots decisively.

This message also demonstrates the value of explicit hypothesis formulation. By writing out the exact byte-level difference between the two paths, the assistant creates a clear target for investigation. The subsequent task to check the VanillaSealProof enum selection is a direct consequence of this hypothesis—a targeted experiment designed to confirm or refute a specific sub-hypothesis.

Conclusion

Message 1671 captures a pivotal moment in a complex debugging session. After exhaustive structural analysis has confirmed parity across every measurable dimension, the assistant steps back and asks a more fundamental question: what is actually different at the byte level between the working and failing paths? The answer—that one path uses Rust's original JSON bytes while the other uses Go's re-serialization—opens a new line of investigation that the subsequent task will pursue.

The message is a testament to the power of systematic reasoning combined with creative insight. It demonstrates that effective debugging requires not just the ability to trace code and compare structures, but the wisdom to recognize when those tools have reached their limits and a new approach is needed. The byte-level divergence hypothesis may or may not lead to the root cause, but it represents the kind of thinking that ultimately resolves the most stubborn bugs: looking not at what the code says, but at what the data actually contains.