The Missing PCE: How a Single Directory Listing Unraveled a PoRep Proving Mystery

In the middle of a complex debugging session spanning constraint system harmonization, GPU pipeline race conditions, and remote deployment logistics, a seemingly mundane user message arrived that would crystallize the investigation's next phase. Message [msg 257] contains nothing more than the output of sudo find /data/zk/ on a remote calibnet host — a recursive directory listing of zero-knowledge parameter files. Yet within this simple output lay the missing piece of evidence that explained why PoRep (Proof of Replication) proofs were failing with random partition invalidity.

The Message in Full

The user, working on a remote host cs-calib, executed:

sudo find /data/zk/

And received a listing of the /data/zk/params directory containing dozens of parameter cache files — verifying keys (.vk), proving parameters (.params), the structured reference string (.srs), and crucially, a single incomplete file:

/data/zk/params/pce-porep-32g.tmp

The absence of a corresponding pce-porep-32g.bin file — the completed Pre-Compiled Constraint Evaluator for the 32GiB PoRep circuit — was the silent scream at the heart of this listing.

Context: The Long Road to This Listing

To understand why this message was written, we must trace the investigation that preceded it. The assistant had been working for multiple rounds on implementing PCE extraction for all proof types (WinningPoSt, WindowPoSt, SnapDeals, and PoRep) in the CuZK proving engine. A critical bug had been discovered and fixed: the RecordingCS constraint system (used during PCE extraction) was not extensible while WitnessCS (used during witness generation) was, causing a mismatch in input counts that crashed WindowPoSt proving. The fix harmonized WitnessCS, RecordingCS, and ProvingAssignment to all start with zero inputs, with the ONE input explicitly allocated by the caller.

After deploying these fixes, the user reported a new problem: PoRep proofs were failing with random partition invalidity. On one run, 7 out of 10 partitions were valid; on a retry, only 1 out of 10. This non-deterministic behavior was deeply suspicious — it pointed away from a synthesis bug (which would be deterministic) and toward a data race, stale state, or randomness issue in the GPU proving path.

The assistant had been investigating this on the remote host. In message [msg 245], it checked for the PCE file and found:

ls: cannot access '/data/zk/params/pce-porep-32g.bin': No such file or directory

And in message [msg 246], it found only a .tmp file:

-rw-r--r-- 1 curio curio 12180815872 Mar  2 06:56 /data/zk/params/pce-porep-32g.tmp

A 12 GB temporary file, but no completed PCE binary. The user's response — the subject message — was to provide the full directory listing, confirming the absence of the completed PCE and showing the complete state of the parameter cache.

Why This Message Was Written: The Reasoning and Motivation

The user had several motivations for sending this directory listing. First, they were providing comprehensive evidence to support the assistant's investigation. The assistant had already discovered the missing .bin file, but the user wanted to show the full picture — all the files that did exist, to confirm that nothing else was missing or corrupted.

Second, the user was implicitly testing a hypothesis. If the PCE file was incomplete, then every PoRep proof attempt would need to regenerate it from scratch. But the logs showed that partitions were using "PCE fast path" — meaning the system thought it had a valid PCE. How could that be? The .tmp file suggested a crashed or interrupted extraction process. Perhaps the daemon was loading the incomplete .tmp file as if it were a valid PCE, or perhaps the PCE was being regenerated in memory each time but failing to persist.

Third, the user was providing operational context. The sudo prefix indicates that the params directory required elevated privileges to access — a detail the assistant had noted earlier when the user said "params need sudo to access" (message [msg 250]). The fact that the .tmp file was owned by curio:curio while the assistant's earlier ls commands may have run without proper permissions explained some of the confusion around file access.

Assumptions Embedded in the Message

The user's message carries several implicit assumptions. The most important is that the directory listing would be interpretable by the assistant — that the assistant would recognize the significance of the missing .bin file and the presence of the .tmp file. This assumption was well-founded, given the assistant's deep engagement with the PCE extraction pipeline.

Another assumption is that the stale build hypothesis was worth pursuing. The binary on the remote host was dated March 1, 20:54 UTC — built before the WitnessCS::new() fix. The user's suggestion in message [msg 247] ("Maybe update cuzk there first?") indicated a belief that deploying the latest code might resolve the partition failures. The directory listing was a prelude to that deployment effort — showing the state of the params directory before the service was restarted with a new binary.

The user also assumed that the assistant would need to see the complete file listing to rule out other missing dependencies. The params directory contains dozens of verifying keys and parameter files for various proof types (PoRep, PoSt, empty sector updates). By showing everything, the user was saying: "Here is the full state of the system — nothing is hidden."

What the Message Revealed: Input and Output Knowledge

Input knowledge required to understand this message: To interpret this listing, one needs to understand the CuZK proving architecture. The .params files are Groth16 proving parameters (the CRS — common reference string). The .vk files are verifying keys. The .srs file is the structured reference string used for inner-product arguments. The pce-porep-32g.tmp file is a Pre-Compiled Constraint Evaluator in its temporary, incomplete state — a serialized representation of the circuit constraints that allows the prover to skip full synthesis and jump directly to witness generation.

One also needs to know the history: that the assistant had recently implemented PCE extraction for PoRep (among other proof types), that the extraction process writes to a .tmp file and then atomically renames to .bin upon completion, and that an incomplete .tmp file indicates a crash or interruption during extraction.

Output knowledge created by this message: The message confirmed definitively that the PoRep PCE had never been successfully extracted and persisted to disk. This explained the random partition failures: without a valid PCE, the system might be falling back to a different synthesis path, or worse, attempting to use the corrupted .tmp file as if it were valid. The non-deterministic behavior could arise from concurrent access to the incomplete file — multiple partitions racing to read or write the same .tmp file, producing inconsistent results.

The listing also revealed that the system had all the standard parameter files it needed for vanilla proving (the .params and .vk files for PoRep 32GiB were present). The problem was specifically in the PCE fast path, not in the underlying cryptographic parameters.

The Thinking Process Visible in the Conversation

Looking at the surrounding conversation, we can see the assistant's reasoning evolve. In message [msg 241], the assistant hypothesized that the non-determinism "can't be a PCE issue (PCE is deterministic)" — but this was before confirming whether the PCE actually existed on disk. By message <msg id=245-246>, the assistant discovered the missing .bin file and the orphaned .tmp file, and the investigation pivoted.

The user's message was the final confirmation. It transformed the hypothesis from "maybe the PCE is corrupted" to "the PCE was never successfully generated." This is a crucial distinction: a corrupted PCE might produce deterministic wrong results, but a missing PCE that the system thinks exists (perhaps loading the .tmp as if complete) could produce the non-deterministic behavior observed.

Mistakes and Incorrect Assumptions

The assistant had made an earlier assumption that the PCE was being loaded from disk successfully because the logs said "using PCE fast path." But the logs only indicated that the path was taken — they didn't verify the integrity of the loaded PCE. The missing .bin file suggested that either:

1. The PCE was being regenerated in memory each time (perhaps from the .tmp file or from scratch) but failing to persist due to permissions or crashes.
2. The system was silently falling back to a different code path that didn't require the persisted PCE.
3. The .tmp file was being treated as valid, leading to undefined behavior when multiple threads accessed it concurrently. The user's message helped correct this assumption by providing ground truth about the filesystem state.

Significance in the Broader Investigation

This message represents a turning point in the debugging session. Before it, the assistant was investigating whether the WitnessCS::new() fix had introduced a regression for PoRep (which doesn't use synthesize_extendable). After it, the focus shifted to the deployment process itself: building the latest code, deploying it to the remote host, cleaning the stale PCE state, and restarting the service to regenerate the PCE from scratch.

The directory listing also served as a baseline. After the deployment, the assistant would need to verify that a fresh pce-porep-32g.bin appeared, with the correct number of inputs (328, as later confirmed). The .tmp file would need to be deleted to prevent any confusion. The listing showed exactly what "clean" looked like — and what needed to change.

Conclusion

Message [msg 257] is a masterclass in the power of simple, direct evidence in debugging. No elaborate theory, no complex log analysis — just the raw output of find showing a directory tree. Yet within that output was the answer to a question that had been puzzling the assistant for multiple rounds: why were PoRep partitions randomly failing? The missing .bin file, the orphaned .tmp file, and the complete set of supporting parameter files told a story that no amount of log parsing could fully reveal. Sometimes the most profound debugging insights come not from sophisticated tooling, but from looking at what is — and isn't — on the disk.