The Expected Failure That Proved Everything Works

=== Proof Result ===
status:    FAILED
job_id:    083c6109-b2fe-4033-8ce1-01a2952f5b26
error:     seal_commit_phase2 failed

At first glance, message [msg 179] appears to be a report of failure. The cuzk-bench tool submitted a PoRep C2 proof request to the freshly started daemon, and the answer came back unambiguous: FAILED. The error string — seal_commit_phase2 failed — is terse, almost dismissive. But in the context of the broader session, this single message represents a critical milestone: the first successful end-to-end traversal of the entire gRPC pipeline for the cuzk proving engine, from client binary through protobuf serialization, network transport, server dispatch, priority scheduling, and into the real Filecoin proving library's FFI boundary. The failure was not a bug; it was a deliberate, expected validation that every layer of the architecture was wired correctly.

The Long Road to a Single Command

To understand why this message was written, one must trace the session's arc. The assistant had spent the preceding hours building the Phase 0 scaffold of cuzk — a pipelined SNARK proving daemon designed to address the structural bottlenecks identified in earlier optimization proposals. The workspace comprised six Rust crates spanning protobuf definitions, core engine logic, gRPC service handlers, a daemon binary, a benchmarking client, and FFI bindings. Twenty source files had been written, compiled, and tested. The prover module had been wired to call filecoin_proofs_api::seal::seal_commit_phase2() — the real Groth16 proof generation function used in production Filecoin storage proving.

But compilation success is not integration success. The assistant needed to validate that the entire chain worked: that a 51 MB C1 proof input could be loaded from disk, serialized into a protobuf message, sent over gRPC within the 128 MiB message limit that had been explicitly configured, deserialized by the server, decoded from base64, parsed into the internal SealCommitPhase1Output structure, dispatched through the priority scheduler to a GPU worker, and finally handed to the real seal_commit_phase2 function. Message [msg 179] is the moment that validation happened.

The Deliberate Decision to Test Without Parameters

A key assumption underpinning this test was that the 32 GiB Groth16 parameters were not required to validate the pipeline. The assistant had checked the parameter cache earlier ([msg 159]) and found it empty — no v28-stacked-proof-of-replication params for 32 GiB sectors existed on the machine. Rather than spending the considerable time required to download ~47 GiB of parameter files from IPFS, the assistant made a deliberate engineering judgment: run the test anyway, knowing it would fail at the final FFI call, and use that failure to prove everything before that call worked correctly.

This was a risk-aware decision. If the pipeline had a bug anywhere in the gRPC layer, the deserialization logic, or the scheduler, the error would manifest differently — a connection failure, a protobuf decode error, a timeout, a panic. The specific error seal_commit_phase2 failed was precisely what the assistant needed to see. It meant that the input had successfully traversed every layer of the stack and reached the real proving function, which then failed because the parameter files it needed to load into GPU memory were absent. The error was propagated cleanly back through the entire chain, preserving the original error message from the FFI layer.

Resolving Shell Complexity to Get a Clean Result

The path to this clean result was not straightforward. Earlier attempts to run the end-to-end test had been thwarted by shell behavior: background processes consuming output, stale daemon instances holding ports, and log files not being written as expected. Messages [msg 163] through [msg 177] document a troubleshooting spiral where the assistant tried increasingly elaborate approaches — redirecting to log files, using nohup, writing a shell script — only to find that the shell environment was swallowing output or that previous daemon processes were still bound to ports.

The breakthrough came in message [msg 177], where the assistant abandoned the script approach and ran the daemon directly in the foreground with &, then verified it was listening with ss -tlnp. This produced visible daemon startup logs confirming the engine was running on port 9827. Message [msg 178] then confirmed the gRPC status endpoint worked: proofs completed: 0, proofs failed: 0. The stage was set for the actual proof submission.

What the Output Reveals About the Architecture

The output of message [msg 179] contains three fields that each tell a story:

status: FAILED — This is not a gRPC-level error. The daemon accepted the request, processed it, and returned a proper response with a failure status. This proves the bidirectional communication works: the client sent a 51 MB protobuf, the server acknowledged it, performed work, and returned a structured result.

job_id: 083c6109-b2fe-4033-8ce1-01a2952f5b26 — The presence of a UUID job ID confirms that the scheduler assigned a unique identifier to the request, which is essential for the daemon's job-tracking and metrics infrastructure. This ID would later appear in Prometheus metrics, linking the failed proof to the counter increment.

error: seal_commit_phase2 failed — This error string originated from the Rust FFI call into filecoin-proofs-api. Its preservation through the entire return path — from the prover worker, through the engine's result channel, into the gRPC response protobuf, and back to the client's formatted output — validates the error propagation design. No error was swallowed, no generic "internal error" replaced the specific message.

The subsequent message [msg 180] confirmed that the daemon's Prometheus metrics correctly recorded the failure: cuzk_proofs_failed_total 1. The monitoring infrastructure, which exposes metrics in Prometheus exposition format, was operational and accurate.

The Knowledge Created by a Failed Proof

Message [msg 179] produced several forms of knowledge that were unavailable before:

  1. gRPC message size handling works. The 128 MiB limit set in messages [msg 151] through [msg 155] was sufficient for the 51 MB C1 input. No truncation, no ResourceExhausted errors.
  2. Protobuf serialization round-trip is correct. The C1 wrapper JSON, containing base64-encoded binary data, was deserialized on the server side without error. The types defined in cuzk-proto matched the actual data format.
  3. The priority scheduler dispatches correctly. The proof request was routed to a GPU worker thread and executed, rather than hanging or deadlocking.
  4. The FFI boundary is correctly wired. The call to seal_commit_phase2 was reached, meaning the filecoin-proofs-api Rust crate was linked, the function signature matched, and the argument types were compatible.
  5. Error propagation is lossless. The specific error from the proving library survived the return trip through async channels, protobuf serialization, and network transport.
  6. The daemon survives failure. After the failed proof, the daemon remained running and responsive to subsequent status and metrics queries. A single proof failure did not crash the process or corrupt its internal state.

The Assumption That Was Partially Wrong

The assistant's assumption that the test could proceed without parameters was correct in the narrow sense — the pipeline was validated — but it created an incomplete picture. The test could not verify that the GPU kernels actually executed, that memory allocation succeeded, or that the proof output was correctly serialized into the response. These aspects remained untested until the parameters were available.

Moreover, the assistant initially assumed that the parameters could be fetched easily afterward. Message [msg 184] shows the user running curio fetch-params 32GiB, which encountered a path resolution bug: the tool downloaded files to a relative path under the current working directory (~/scrot/) instead of the intended absolute path (/data/zk/params/). This led to a cascade of "sanity checking fetched file failed" errors because the files were written to the wrong location. The assistant had to diagnose this issue and manually copy the files to the correct directory, as documented in the chunk summary.

The Thinking Process Behind the Test

The assistant's reasoning in the lead-up to message [msg 179] reveals a systematic approach to integration testing. After the daemon was confirmed running on port 9827 ([msg 177]), the assistant first verified the simplest RPC — status — to confirm basic gRPC connectivity ([msg 178]). Only then did it escalate to the full proof submission. This incremental strategy — test connectivity, test simple query, test complex operation — is a classic integration testing pattern that minimizes ambiguity when something goes wrong.

The choice of --log-level warn for the bench client (rather than info or debug) was intentional: it suppressed verbose output from the gRPC library and the prover internals, producing a clean, parseable result block. The assistant wanted a single, unambiguous signal: did the proof succeed or fail, and what was the error? This signal was then immediately cross-referenced with the daemon's metrics endpoint to confirm consistency.

Conclusion

Message [msg 179] is a study in how a "failed" test can be more valuable than a passing one. The failure was expected, designed for, and precisely interpreted. It validated the entire software stack from client to FFI, proved the error handling architecture, and confirmed the monitoring infrastructure — all without requiring the 47 GiB of parameter files that would have been needed for a genuine proof. The message stands as the culmination of Phase 0 implementation, the moment when the cuzk daemon transitioned from a collection of compiling source files to a running system that demonstrably processes real-world proof requests. The next step — fetching parameters and running a successful proof — was a matter of environmental setup, not architectural uncertainty.