The Binary That Wouldn't Change: A Lesson in Docker Build Caches and Silent Deployment Failures

In the high-stakes world of distributed GPU proving systems for Filecoin, a single character can make the difference between valid proofs and corrupted partitions. Message [msg 2008] captures a pivotal moment in a debugging odyssey where the assistant, having identified and fixed a critical job ID collision bug, discovers that the fix never actually made it into the running binary. The message is a single SSH command — a verification step that doubles as a deployment attempt — and its output reveals a stark truth: the assistant's carefully crafted fix was still sitting on the build server, never deployed.

The Context: A Job ID Collision Crisis

To understand the weight of this moment, we must trace the narrative that led here. The ProofShare system in Curio (a Filecoin storage provider implementation) enables miners to prove storage commitments using a GPU-accelerated proving engine called cuzk. The system works by dispatching concurrent "PSProve" tasks, each of which computes a Proof-of-Replication (PoRep) across multiple partitions. These tasks communicate with the cuzk daemon via a request identifier — the RequestId — which the engine uses as a key to assemble partition results into a complete proof.

The bug was subtle and devastating. All proofshare challenges target a single hardcoded benchmark sector (miner=1000, sector=1). The RequestId was formatted as fmt.Sprintf("ps-porep-%d-%d", sectorID.Miner, sectorID.Number) — producing the string ps-porep-1000-1 for every single task. When multiple PSProve tasks ran concurrently, they all sent identical job_id values to cuzk. The engine's partition assembler, which used a HashMap keyed on job_id, would receive partition results from different proofs and mix them together. The symptom was unmistakable: a "partition 0 already inserted" panic in the cuzk engine logs, followed by invalid proofs for all ten partitions.

The fix was straightforward: add the harmony task ID to the format string, producing ps-porep-%d-%d-%d (miner, sector, taskID). This matched the pattern already used by the SnapDeals path, which had never exhibited the bug. The assistant had already verified the non-proofshare cuzk path (normal PoRep C2) was safe because real sectors always have unique miner+sector combinations.

The Deployment That Wasn't

The assistant's first deployment attempt used a --volumes-from Docker strategy: create a container from the curio-builder image, use docker cp to overwrite the modified source files, then run a build container with --volumes-from to access those files. This produced binary curio-psfix2, which was uploaded and installed. The assistant confirmed the version string showed _psfix2 and started the new curio process.

But the user reported that cuzk logs still showed ps-porep-1000-1 — the old format. The assistant verified by grepping the binary on the remote host and found ps-porep-%d-%d with only two %d specifiers. The Go build cache had not recompiled the changed files.

The root cause was a subtle Docker behavior: docker cp copies files into the container's writable layer, but --volumes-from only shares named volumes declared in the Dockerfile. The curio-builder image had no VOLUME directive for /build, so the copied source files were invisible to the build container. The Go compiler, seeing no changes to the source files, happily served up cached object files from the original image layers. The touch command that the assistant added to bust the cache was equally ineffective — it operated on files that the build container couldn't see.

Message 2008: The Verification That Exposed the Truth

Message [msg 2008] is the assistant's second deployment attempt. Having identified the --volumes-from problem in the previous round ([msg 2005]), the assistant switched to direct bind mounts (-v) for the modified source files. The build in [msg 2005] confirmed the fix was compiled in — grep found ps-porep-%d-%d-%d with three format specifiers. The binary was uploaded via scp in [msg 2006]. Then, in [msg 2007], the assistant attempted to deploy with a chained command:

kill $(pgrep -f "curio run") 2>/dev/null; sleep 2; mv /tmp/curio-psfix3 /usr/local/bin/curio && chmod +x /usr/local/bin/curio && grep -ao "ps-porep-%d-%d[^\"]*" /usr/local/bin/curio | head -1 && curio --version 2>&1

The output was empty — a silent failure that the assistant did not catch.

Message [msg 2008] is the follow-up. The assistant runs a combined SSH command that does three things in sequence: (1) greps the binary for the format string to verify the fix is compiled in, (2) checks the version, (3) starts curio and confirms it's running. The command is:

grep -ao "ps-porep-%d-%d[^\"]*" /usr/local/bin/curio | head -1; curio --version 2>&1; nohup curio run --listen 0.0.0.0:2036 > /tmp/curio.log 2>&1 & sleep 2; pgrep -a curio

The output is devastating:

ps-porep-%d-%dRSealProvFinalCommR mismatchstorage-marketAggregateDeals...

The format string still has only two %d specifiers. The version (not shown in the output but inferred from context) still says _psfix2. The binary was never replaced.

The grep output is particularly revealing. Because the binary is stripped (-s -w in the linker flags), grep -a treats it as text and finds the format string embedded among surrounding binary noise. The output shows ps-porep-%d-%d followed immediately by unrelated strings like RSealProvFinalCommR mismatch — these are adjacent bytes in the binary that happen to follow the null-terminated format string. It's a raw, unfiltered view into the compiled artifact, and it confirms beyond doubt that the fix is absent.

Why the Deployment Failed

The assistant's reasoning in the following message ([msg 2009]) identifies the problem: the kill and mv were chained with &&, and the kill command may have succeeded (sending the signal) but the process didn't die before mv ran, causing the file move to fail because the running process had the binary file locked. The sleep 2 should have been sufficient, but the kill command in the previous round may have been sent to a process that had already been restarted or had a different PID.

More fundamentally, the assistant's deployment workflow had a critical flaw: it chained destructive operations (kill, mv) without capturing their exit codes or output. When the output was empty, the assistant moved on without verifying that each step succeeded. This is a common pitfall in remote SSH-based deployments, where silent failures can cascade unnoticed.

The Thinking Process Revealed

The assistant's reasoning in [msg 2005] shows a sophisticated understanding of Docker internals. The assistant correctly identifies that --volumes-from only shares declared volumes, not the entire container filesystem. The assistant considers alternatives — docker commit, bind mounts — and chooses the correct approach. This diagnostic thinking is what ultimately leads to the successful build.

However, the assistant also makes an incorrect assumption: that because the build succeeded and produced a binary with the correct format string, the deployment would also succeed. The assistant does not anticipate that the mv command could fail silently, and does not add error checking to the deployment chain.

Input Knowledge Required

To understand this message, one needs knowledge of:

Output Knowledge Created

This message creates critical knowledge about the state of the deployment: the fix is not in place. It forces the assistant to re-examine the deployment process and identify the silent failure. The message also serves as a cautionary tale about the fragility of SSH-based deployments and the importance of verifying each step independently.

The Broader Significance

This moment exemplifies the operational complexity of patching GPU-proving systems in production. Unlike a typical web service where you can do a rolling restart, the cuzk pipeline processes proofs in-flight, and killing the wrong process can corrupt hours of computation. The assistant must coordinate between multiple systems — the Go Curio binary, the Rust cuzk daemon, the Docker build environment, and the remote SSH host — each with its own caching, locking, and failure modes.

The fix itself is a single line change: adding taskID to a format string. But getting that change into the running binary requires navigating Docker build caches, SSH silent failures, file locking semantics, and process management. The assistant's systematic approach — verifying the binary's format string before and after deployment, checking hashes, and reasoning about Docker internals — demonstrates the rigor required for production debugging in distributed systems.

In the end, the assistant will succeed. The next deployment will use proper error checking, the binary will be replaced, and the ps-porep-%d-%d-%d format will produce unique job IDs for every concurrent task. But message [msg 2008] stands as a monument to the moment before success — the moment when all the evidence says the fix should be working, but the binary stubbornly refuses to change.