The Invisible Bridge: How a Single docker cp Command Carried a Production Fix Across the GPU Proving Pipeline

In the high-stakes world of Filecoin GPU proving, where a single invalid proof can cascade into lost collateral and failed storage deals, the difference between a correct fix and a deployed fix is an entire operational pipeline. Message [msg 1986] captures this transition in its most elemental form: a docker cp command that copies three modified Go source files into a build container. The command itself is unremarkable—four lines, one echoed word of confirmation—but it sits at the precise inflection point where root-cause analysis becomes remediation, where debugging ends and deployment begins.

[assistant] [bash] docker cp /tmp/czk/tasks/proofshare/task_request.go curio-rebuild2:/build/tasks/proofshare/task_request.go && docker cp /tmp/czk/tasks/proofshare/task_prove.go curio-rebuild2:/build/tasks/proofshare/task_prove.go && docker cp /tmp/czk/lib/proofsvc/provictl.go curio-rebuild2:/build/lib/proofsvc/provictl.go && echo "copied"
copied

To understand why this message matters, one must first understand the bug it aims to fix. The ProofShare system is a distributed proving protocol where multiple concurrent "PSProve" tasks generate GPU proofs for Filecoin sectors. Each task sends a RequestId to the cuzk proving engine, which uses it as a key in its internal JobTracker.assemblers HashMap to collect and assemble partition proofs. The problem, identified in the preceding messages ([msg 1977], [msg 1978]), was that all PSProve challenges targeted the same benchmark sector—miner=1000, sector=1—and the RequestId was formatted as "ps-porep-%d-%d" using only these two values. Every concurrent task sent the identical job_id = "ps-porep-1000-1" to cuzk. The engine's assembler, keyed on this shared identifier, mixed partition results from different proofs, producing the characteristic panic "partition 0 already inserted" and rendering all ten partitions invalid. When the user constrained parallelism to a single task (proofshare_max_tasks=1), proofs emerged correct—confirming the collision hypothesis beyond doubt.

The fix itself was surgically precise. The assistant modified computePoRep in task_prove.go to thread the harmony taskID into the RequestId format string, changing it from "ps-porep-%d-%d" to "ps-porep-%d-%d-%d" ([msg 1980]–[msg 1982]). The non-proofshare path in lib/ffi/cuzk_funcs.go was audited and found safe because normal PoRep C2 jobs already carry unique sector identities. But a correct fix on disk is not a deployed fix. The code lives on the assistant's local filesystem at /tmp/czk/, while the production environment is a remote GPU host running a CUDA 13.0.2 Docker container with specialized GPU libraries for supraseal, bellperson, and the full Filecoin proving stack. The build cannot happen locally.

The Operational Bridge

This is where message [msg 1986] enters. The container curio-rebuild2 was created moments earlier ([msg 1985]) from the curio-builder:latest image, which contains the full Curio source tree and all CUDA build dependencies. The assistant's decision to use docker cp rather than rebuilding the entire Docker image reflects a deliberate trade-off between speed and isolation. A full image rebuild would require pushing a new Dockerfile to a registry, pulling it on the build host, and waiting for the multi-stage build to complete—potentially tens of minutes. Copying individual files into an existing container and compiling in-place collapses this to a single go build command ([msg 1987]), which completes in seconds for the Go portions (the Rust cuzk binary was already separately deployed in earlier messages).

The three files chosen reveal the scope of the fix. task_prove.go contains the computePoRep function where the RequestId format was corrected. task_request.go likely carries complementary changes—perhaps the deadlock fix for CreateWorkAsk that was also being addressed in this chunk (the HTTP 429 retry loop that blocked the poll loop from discovering matched work). provictl.go from lib/proofsvc/ suggests an interface or client change needed to support the modified call signature, since computePoRep now accepts a harmonytask.TaskID parameter that must be propagated through the proof service client layer.

Assumptions and Their Consequences

The message operates on several assumptions, some of which proved fragile. First, that the Docker container's filesystem is writable and docker cp will silently overwrite the existing source files—this held true. Second, that the Go build cache within the container would detect the modified timestamps and recompile the affected packages—this also held, as the subsequent build succeeded ([msg 1987]). Third, that these three files represent the complete set of changes needed—a reasonable inference given the compiler's ability to detect missing symbols, but one that depends on the developer having correctly traced all call sites.

A more subtle assumption concerns the build environment's reproducibility. The curio-builder:latest image was built at some earlier point with specific versions of all dependencies. By injecting modified source files into a pre-existing container, the assistant implicitly trusts that no other changes in the source tree (e.g., to go.mod, to build scripts, to C headers) are needed and that the container's cached compilation artifacts are compatible with the patched code. This is generally safe for Go projects where dependencies are vendored or version-locked, but it introduces a latent risk: if the container's build cache contains stale artifacts from a different codebase version, the resulting binary could be an inconsistent hybrid. The subsequent verification—grepping the binary for the old format string and checking process hashes—mitigates this risk but does not eliminate it.

The Thinking Process Behind the Message

The assistant's reasoning in [msg 1978] reveals the investigative path that led to this moment. The chain of inference is worth tracing: the user reported that all ten partitions were invalid with parallelism but correct with proofshare_max_tasks=1. The assistant immediately connected this to the job_id derivation, noting that "challenge sectors from cusvc/powsrv are ALL miner=1000, sector=1." It then mapped this to the engine's internal architecture: "The job_id serves as a key in the engine's JobTracker.assemblers HashMap, so when concurrent proofs share the same job_id, their partition results collide and overwrite each other." The "partition 0 already inserted" panic was the confirming signal—a smoking gun that the assembler had already registered a result for that partition under the same key.

The assistant also demonstrated systematic thinking by checking whether the same vulnerability existed in the non-proofshare path. It found that lib/ffi/cuzk_funcs.go uses a different format ("porep-%d-%d") but for normal PoRep C2 jobs that have unique sector identities, making the collision impossible in practice. This audit—completed before the first build attempt—prevented a partial fix that would have left other paths exposed.

Input and Output Knowledge

To fully understand this message, one must grasp several layers of context: the architecture of the ProofShare system (Go Curio daemon coordinating GPU proving tasks via a Rust cuzk engine over gRPC), the role of RequestId as a partitioning key in the engine's assembler, the constraint that all PSProve challenges target the same benchmark sector, and the operational reality that GPU builds require a CUDA-capable Docker environment unavailable on the assistant's local machine. The message also presupposes familiarity with Docker's cp subcommand, the --volumes-from pattern for sharing build artifacts, and the Go toolchain's behavior with modified source files.

The knowledge created by this message is deceptively modest: a container with three patched files and a confirmation echo. But this is the substrate on which everything else depends. Without this copy operation, the subsequent build ([msg 1987]), the SCP transfer ([msg 1988]), and the deployment ([msg 1989]) cannot proceed. The message is the first link in a deployment chain that ultimately places a corrected binary on a remote GPU host in Belgium, fixing a production bug where concurrent proofshare tasks were silently producing invalid proofs that could have compromised the entire ProofShare protocol.

The deployment itself was not without friction. In [msg 1989], the kill + mv chain produced only a partial output—the curio PID was visible but the version string was not, suggesting that the running process may have interfered with the binary replacement. This is a recurring theme in the session: the tension between rapid iteration and operational reliability, between the clean abstraction of a Docker build and the messy reality of hot-swapping binaries on a remote production host. The docker cp command in [msg 1986] represents the clean, controlled part of the pipeline. What follows is where engineering meets entropy.