The Remote Build: Deploying PCE Fixes to the Calibnet Host

In the course of a multi-hour debugging session spanning constraint system harmonization, GPU proving pipeline analysis, and remote deployment, one message stands out as the pivotal inflection point where theory met practice. Message [msg 264] is a single bash command executed on a remote calibnet test host:

ssh 10.1.16.218 'export PATH=/home/theuser/.cargo/bin:/usr/local/cuda-13.0/bin:$PATH && export CC=gcc-13 && export CXX=g++-13 && export NVCC_PREPEND_FLAGS="-ccbin /usr/bin/g++-13" && cd /tmp/czk/extern/cuzk && cargo build --release -p cuzk-daemon 2>&1 | tail -30'

The output shows only compiler warnings — two instances of the same note about JobTracker being more private than the function process_monolithic_result that uses it. No errors. The build succeeded.

This message is deceptively simple. It is a cargo build invocation, but it represents the culmination of hours of diagnostic work, the deployment of a three-way fix to a subtle constraint system inconsistency, and the beginning of a new phase of investigation into a separate, pre-existing GPU race condition. To understand its significance, one must trace the threads that converged at this moment.

Context: The Stale Build and the Corrupted PCE

The remote host at 10.1.16.218 was running a cuzk-daemon binary built on March 1, before the critical WitnessCS::new() and RecordingCS::new() fixes were introduced. The assistant had discovered this earlier when examining the binary's modification timestamp ([msg 245]). More tellingly, the PoRep PCE file on disk was incomplete — only a .tmp file existed at /data/zk/params/pce-porep-32g.tmp ([msg 246]), suggesting a previous extraction had been interrupted or corrupted.

The user had been observing random PoRep partition failures: proofs that passed verification on some runs but failed on others, with the set of valid partitions changing non-deterministically between retries. This pattern was deeply puzzling — a correct synthesis should produce deterministic results. The assistant initially hypothesized that the stale build might be the culprit, perhaps combined with a corrupted PCE file. The user's suggestion at [msg 247] — "Maybe update cuzk there first?" — crystallized the next step: deploy the latest code, clean the stale state, and see if the problem resolved.

Anatomy of the Build Command

The build command itself is a carefully constructed invocation that reflects the assistant's prior reconnaissance of the remote environment. Earlier probing had revealed that cargo was not in the default PATH — it lived under /home/theuser/.cargo/bin ([msg 255]). CUDA 13.0 was installed at /usr/local/cuda-13.0/bin. The system compiler was gcc-13, and CUDA required explicit -ccbin flags to use it ([msg 259]).

Every environment variable serves a purpose:

The Output: Warnings, Not Errors

The build output shows two warnings, both concerning the JobTracker type in cuzk-core/src/engine.rs. The type is declared as struct JobTracker (private by default), but it is used in the signature of pub(crate) fn process_monolithic_result, which has broader visibility. Rust's private_interfaces lint (enabled by default) warns about this because changing JobTracker's fields would require updating all callers, even though they can't name the type directly.

These warnings are pre-existing and unrelated to the assistant's changes. Their presence in the output is actually good news: it means the build completed without errors, and the only diagnostics are cosmetic lints that don't affect correctness or performance. The assistant's fixes — the WitnessCS::new() change, the RecordingCS::new() change, the PCE extraction wiring for all proof types, and the SnapDeals partitioned pipeline — all compiled cleanly with the CUDA 13.0 / gcc-13 toolchain on Ubuntu 24.04.

What This Build Enabled

With the binary successfully compiled, the assistant proceeded to deploy it in the next message ([msg 265]): stopping the cuzk service, copying the new binary to /usr/local/bin/cuzk, removing the stale PCE files (pce-porep-32g.tmp and any .bin files), and restarting the service. The deployment was clean — the service started successfully and was reported as active.

The subsequent monitoring ([msg 270]) confirmed the core achievement: background PCE extraction for PoRep completed correctly, producing a PreCompiledCircuit with inputs: 328, aux: 130169893, and constraints: 130278869. This matched the expected dimensions for a PoRep 32GiB circuit, confirming that the harmonization of WitnessCS, RecordingCS, and ProvingAssignment had resolved the structural mismatches that had been causing crashes and incorrect witness generation.

Assumptions and Their Validation

The build command embodied several assumptions, most of which proved correct:

  1. The remote environment is compatible: The assistant assumed that the Rust toolchain under /home/theuser/.cargo/bin (version 1.93.1) could compile the workspace, and that CUDA 13.0 with gcc-13 would produce working GPU kernels. Both held.
  2. The warnings are harmless: The JobTracker visibility warnings were assumed to be pre-existing and non-critical. This was correct — the deployed binary functioned correctly.
  3. The stale build was the likely cause of PoRep failures: This assumption turned out to be incorrect. After deploying the fresh build and observing the same random partition invalidity pattern, the assistant correctly diagnosed the issue as a pre-existing GPU race condition unrelated to the PCE/WitnessCS changes ([msg 272]). The pattern of only the first two GPU-processed partitions succeeding, with the rest failing non-deterministically, pointed to a concurrency issue in the multi-GPU worker interlock — likely related to CUDA_VISIBLE_DEVICES being set concurrently by multiple workers sharing a device.
  4. Cleaning the stale PCE state would help: The .tmp file was removed, and the new PCE extraction produced a correct circuit. This assumption was validated.

The Broader Significance

Message [msg 264] sits at the boundary between two phases of the session. Before it, the assistant had been diagnosing and fixing constraint system inconsistencies in the abstract — reasoning about CS::new() behavior, tracing extend() semantics, and harmonizing three different constraint system implementations. After it, the assistant entered a deployment and validation phase, where those fixes met real hardware and real proofs.

The build's success was not guaranteed. Cross-compilation or environment mismatches could easily have derailed it: a different CUDA version, an incompatible GCC, missing system libraries, or a Rust edition mismatch. The assistant's careful reconnaissance of the remote environment — finding the cargo binary under the theuser user, confirming the CUDA path, testing the compiler — was essential to getting this right in a single attempt.

More importantly, the build's success enabled the critical diagnostic insight that followed: the PoRep partition failures were not caused by the PCE or WitnessCS changes. By deploying the latest code and observing the same failure pattern, the assistant ruled out the most likely hypotheses and isolated the true root cause — a pre-existing GPU race condition. This separation of concerns — "our fix works, the remaining bug is pre-existing" — was the key outcome that this build made possible.

In the broader arc of the session, message [msg 264] represents the moment when months of constraint system engineering were validated against real hardware, and when the remaining challenge was cleanly identified for future investigation.