The Phantom Deployment: When a Production Fix Doesn't Take Hold

In the high-stakes world of distributed GPU proving systems, deploying a bug fix is rarely as simple as shipping a binary. Message 1990 of this opencode session captures a moment of operational tension: a carefully crafted fix for a critical proof-collision bug has been built, copied to a remote server, and ostensibly installed — yet when the assistant checks, the old binary remains stubbornly in place, and the old process is still running. This message is a masterclass in the discipline of verification, revealing how even straightforward deployment commands can fail silently, and why the most important step in any production fix is confirming that the fix actually took.

The Bug That Demanded a Fix

To understand the significance of this message, we must first understand what preceded it. The ProofShare system — a distributed proving protocol for Filecoin — was experiencing a catastrophic failure mode. When multiple concurrent proof challenges targeted the same sector (miner=1000, sector=1), all ten partitions of every proof came back invalid. The user had demonstrated that setting proofshare_max_tasks=1 (serializing the work) produced correct proofs, while any parallelism caused total failure.

The assistant traced the root cause to a job ID collision. The cuzk proving engine's JobTracker used a HashMap keyed on job_id to assemble partition results. The job_id was generated from the miner and sector IDs alone — ps-porep-1000-1 — which was identical for every concurrent challenge. When two parallel proofs submitted their partition results under the same key, they overwrote each other. The Rust-side panic message said it all: "partition 0 already inserted".

The fix was surgical: add the harmony task ID to the RequestId format string, changing it from ps-porep-%d-%d to ps-porep-%d-%d-%d, ensuring each concurrent invocation had a unique identifier. The assistant had already verified that the non-proofshare path (normal PoRep C2) was safe because it used real, unique sector IDs. The fix compiled cleanly, and a new binary — curio-psfix2 — was built inside a Docker container and copied to the remote host via SCP.

The Message: A Deployment Unravels

Message 1990 is where the assistant checks whether the deployment actually succeeded. It opens with agent reasoning that reveals immediate suspicion:

The command seems to have stopped curio but didn't output the version. Let me check if it was successful.

This is the voice of experience. The previous command (message 1989) had chained several operations: capture the PID, kill the process, sleep, move the old binary to a backup name, move the new binary into place, set permissions, and print the version. But the only output was curio PID=207365 — the kill succeeded, but the version check never printed. A junior engineer might have assumed the rest worked silently. The assistant knows better.

The verification command that follows is straightforward but devastating:

ssh -p 40362 root@141.195.21.72 'curio --version 2>&1; ls -la /usr/local/bin/curio; pgrep -a curio || echo "curio stopped"'

And the output tells the whole story:

Error parsing language
curio version 1.27.3-rc2+mainnet+git_96f6c783_2026-03-11T16:08:33+01:00_psfix
-rwxr-xr-x 1 root root 170410824 Mar 13 08:48 /usr/local/bin/curio
206252 curio-old-proofshare run --listen 0.0.0.0:2036

Three damning facts emerge from this output. First, the version string reads _psfix, not _psfix2 — the new binary was never installed. Second, the file timestamp is Mar 13 08:48, matching the first build, not the freshly built psfix2. Third, there is still a running process — not even the main curio binary, but the old binary renamed to curio-old-proofshare from a previous deployment attempt, still serving requests on port 2036.

The Reasoning: What Went Wrong

The assistant's reasoning in this message reveals a systematic diagnostic approach. Rather than jumping to conclusions, it walks through the evidence:

The version string says _psfix not _psfix2 — the build-time version tag embedded in the binary doesn't match
The binary size (170,410,824 bytes) matches the old binary, not the ~163MB psfix2 build
The file timestamp (08:48) predates the psfix2 build, which happened around 10:06
There's a running curio-old-proofshare process — evidence of a prior deployment that renamed the old binary but never properly cleaned up The assistant correctly infers that the mv commands in the previous deployment step failed silently. The chained command kill $PID; sleep 2; mv ... && mv ... && chmod ... && curio --version likely failed at the first mv because the running process was still holding the file lock, or because the shell pipeline had a subtle error. The key insight is that the command appeared to run (it output curio PID=207365) but the subsequent operations never executed — or if they did, they failed without producing error output visible over SSH.## Assumptions and Their Betrayal This message exposes several assumptions that silently failed. The first is that a chained shell command over SSH is atomic. The command kill $PID; sleep 2; mv A B && mv C A && chmod +x A && curio --version assumes each step depends on the previous one succeeding, but the && chaining means a single failure anywhere stops the entire pipeline. When the first mv failed — likely because the running curio process still held the file descriptor — the rest of the chain silently aborted. No error message propagated because the SSH session captured only the first command's output (curio PID=207365) and the subsequent failures produced no stderr visible to the caller. The second assumption is that killing a process releases its binary immediately. On Linux, a running process keeps its executable file mapped in memory and holds an inode reference. While mv can rename or replace the file (since the process holds a file descriptor, not a lock on the path), the timing matters: if the process hasn't fully exited after kill and sleep 2, the file system operations may behave unpredictably. In this case, the old binary was successfully renamed to curio-psfix1 (as evidenced by the running curio-old-proofshare process — a different rename from an earlier deployment), but the new binary never made it into place. The third assumption is that a single verification command is sufficient. The assistant's instinct to check immediately — rather than assuming success — is what caught the failure. But even the verification command itself reveals an assumption: that curio --version would work. It produced Error parsing language (a quirk of the Go binary's version output interacting with the shell), but the version string was still visible. The assistant had to interpret this ambiguous output correctly.

Input Knowledge Required

To fully understand this message, a reader needs familiarity with several domains. First, the architecture of the ProofShare system: that it uses a cuzk proving engine where partition results are assembled using a job_id key, and that concurrent proofs with identical keys cause data corruption. Second, the Go build and deployment workflow: that the Curio binary is built inside a Docker container with CUDA toolchains, extracted via docker cp, transferred via SCP, and manually placed on the remote host. Third, the SSH command chaining patterns used throughout the session: kill; sleep; mv && mv && chmod && version — a fragile but common pattern for hot-swapping binaries on remote servers.

The reader must also understand the version string convention. The assistant had deliberately embedded _psfix2 in the build via a Go linker flag (-X github.com/filecoin-project/curio/build.CurrentCommit=+git_..._psfix2), creating a forensic marker that would appear in curio --version. This was not cosmetic — it was a deliberate diagnostic tool, allowing the assistant to distinguish between builds at a glance. The fact that the running binary still showed _psfix was the first and most damning piece of evidence.

Output Knowledge Created

This message produces critical operational knowledge. It confirms that the deployment command in message 1989 failed, even though it appeared to succeed. It identifies the specific failure mode: the mv chain aborted silently, leaving the old binary in place and an orphaned old process still running. It establishes the current state of the remote host: the wrong binary is at /usr/local/bin/curio, a stale process is running under a renamed binary, and /tmp/curio-psfix2 still contains the correct fix — but it hasn't been installed.

This knowledge directly drives the next actions. The assistant will need to stop the orphaned process, properly copy the binary, and verify the version string matches _psfix2. The message also creates a broader lesson: chained SSH commands are fragile, and every deployment step should be independently verified.

The Thinking Process: Systematic Diagnosis

The agent reasoning in this message is a model of disciplined troubleshooting. It begins with a hypothesis ("the command seems to have stopped curio but didn't output the version"), then designs a verification experiment (check version, file metadata, and running processes). When the results contradict expectations, it walks through the evidence methodically rather than jumping to a conclusion.

The reasoning also shows the assistant connecting multiple data points. The version string _psfix contradicts the build tag _psfix2. The file size 170MB doesn't match the expected ~163MB. The timestamp 08:48 doesn't match the 10:06 build time. And the running curio-old-proofshare process tells a story about previous deployment attempts. Each data point alone is ambiguous; together, they tell an unambiguous story of deployment failure.

This is the kind of thinking that separates robust engineering from fragile operations. The assistant doesn't assume success — it verifies. And when verification fails, it doesn't panic or retry blindly — it diagnoses.