The Diagnostic Pivot: Tracing a Param Cache Mismatch in the cuzk Benchmark Script

In the course of building and deploying a Docker-based proving stack for Filecoin's Curio/CuZK ecosystem, a seemingly straightforward benchmark script ran into a confounding failure. The user had deployed the Docker image to a remote vast.ai instance, run the benchmark.sh script, and received a cascade of errors: the warmup proof failed because "SRS param file not found," the batch subcommand rejected a -n flag, and the PCE file was nowhere to be found. Message [msg 681] captures the moment the assistant pivots from fixing superficial CLI argument mismatches to diagnosing a deeper, architectural misunderstanding about how the cuzk daemon discovers its parameter directory. This message is a pure diagnostic artifact — no edits are applied, no commands are executed — yet it represents the critical reasoning step that reorients the entire debugging effort.

The Context of Failure

To understand why message [msg 681] was written, one must first appreciate the chain of events leading to it. The assistant had created a benchmark.sh script designed to automate PoRep (Proof of Replication) benchmarking against the cuzk proving daemon. The script downloaded C1 test data, started the daemon, ran a warmup proof to trigger PCE (Pre-Compiled Constraint Evaluator) extraction, and then executed a batch of benchmark proofs. On paper, it was a clean pipeline.

But reality intervened. When the user ran the script on a remote host ([msg 675]), the warmup proof failed with a specific error: "C1 parse failed: SRS param file not found for Porep32G: /data/zk/params/v28-stacked-proof-of-replication-merkletree-poseidon_hasher-8-8-0-sha256_hasher-82a357d2f2ca81dc61bb45f4a762807aedee1b0a53fd6c4e77b46a01bfef7820.params." The daemon was looking for parameters at /data/zk/params, but the benchmark script had been configured to use /var/tmp/filecoin-proof-parameters — the path where the Docker entrypoint's curio fetch-params command had downloaded them. Furthermore, the batch subcommand failed with "unexpected argument '-n' found," revealing that the script was passing short-form flags (-n, -j) that cuzk-bench batch did not recognize.

The assistant's first response ([msg 676]) correctly identified both issues: the daemon's default param path and the CLI flag mismatch. The flag fix was straightforward — replace -n with --count and -j with --concurrency — and was applied in [msg 678]. But the param path issue was subtler, and it is this subtlety that message [msg 681] grapples with.

The Reasoning in Message 681

Message [msg 681] opens with a concise diagnosis:

The daemon defaults param_cache to /data/zk/params (from config). The benchmark script starts the daemon with FIL_PROOFS_PARAMETER_CACHE but the daemon's own default config overrides that. The fix: pass FIL_PROOFS_PARAMETER_CACHE to both the daemon and bench, and also set it as the default PARAM_DIR in the script to match where params actually are.

This paragraph encapsulates the core insight. The assistant had assumed — reasonably — that setting the environment variable FIL_PROOFS_PARAMETER_CACHE would be sufficient to tell the daemon where to find its parameters. After all, this is the standard mechanism used throughout the Filecoin proof ecosystem. But the cuzk daemon, it turns out, reads its configuration from a config struct that has a hard-coded default of /data/zk/params. When the daemon starts without an explicit config file, that default takes precedence over the environment variable. The env var is simply not consulted.

The assistant then reads the benchmark script to verify the current state:

The params are at /var/tmp/filecoin-proof-parameters (from the entrypoint fetch). But the daemon defaults to /data/zk/params. The benchmark script should detect where params actually live: [read] /tmp/czk/docker/cuzk/benchmark.sh

This is a pivotal moment. The assistant is not just identifying a bug — it is recognizing a design flaw in the script's assumptions. The script had been written with a fixed PARAM_DIR variable that defaulted to /var/tmp/filecoin-proof-parameters, but the daemon's internal default was different. The two paths were out of sync, and no amount of env-var setting would fix it because the daemon never read that env var.

Assumptions Made and Broken

Several assumptions underpin the original design of the benchmark script, and message [msg 681] exposes them:

Assumption 1: The daemon respects FIL_PROOFS_PARAMETER_CACHE. This is the most critical broken assumption. Throughout the Filecoin proof stack, FIL_PROOFS_PARAMETER_CACHE is the canonical way to specify where parameters live. The entrypoint script uses it, cuzk-bench uses it, and the broader Curio ecosystem respects it. But the cuzk daemon's configuration layer has its own param_cache field with a default value, and the config loading logic prioritizes that default over the environment variable. The assistant's grep in [msg 680] confirmed that the daemon code references param_cache extensively but never consults FIL_PROOFS_PARAMETER_CACHE at startup.

Assumption 2: The daemon and the benchmark script share a common param path. The script was written with the assumption that the params would be at /var/tmp/filecoin-proof-parameters (the path used by curio fetch-params). But the daemon's config default pointed to /data/zk/params. These paths diverged because the Docker image's entrypoint and the daemon binary were built from different conventions — the entrypoint used the standard Filecoin param cache path, while the daemon's developers had chosen a different default for their config.

Assumption 3: Setting an env var before starting a subprocess is sufficient to configure it. This is a general Unix assumption that fails when the subprocess has its own configuration layer that doesn't fall back to environment variables. The daemon's config struct likely uses a library like serde with a #[serde(default)] annotation, and the default value for param_cache is /data/zk/params. When the config is loaded, that default is applied regardless of any environment variable.

Input Knowledge Required

To fully understand message [msg 681], one needs several pieces of contextual knowledge:

The cuzk daemon's configuration architecture. The daemon uses a config struct with a default param_cache of /data/zk/params. This is not obvious from the daemon's CLI — it only exposes --listen and --config flags, with no --param-cache option. The config is loaded from a file or uses defaults, and the defaults are baked into the struct definition.

The relationship between FIL_PROOFS_PARAMETER_CACHE and the daemon's internal config. In the broader Filecoin ecosystem, FIL_PROOFS_PARAMETER_CACHE is the standard env var for parameter discovery. But the cuzk daemon's codebase does not read this env var at startup — it relies entirely on its config struct. This is an architectural inconsistency between the daemon and the rest of the toolchain.

The benchmark script's structure. The script defines PARAM_DIR early on, uses it to set FIL_PROOFS_PARAMETER_CACHE when starting the daemon, and passes it to cuzk-bench. But because the daemon ignores the env var, the script's efforts are futile.

The Docker entrypoint's param fetch behavior. The entrypoint runs curio fetch-params 32GiB, which downloads parameters to /var/tmp/filecoin-proof-parameters by default. This is the path where params actually exist on the filesystem, but it's not where the daemon looks.

Output Knowledge Created

Message [msg 681] produces several critical pieces of knowledge that shape the subsequent debugging:

The root cause is identified. The failure is not a missing file or a network issue — it is a configuration mismatch between the daemon's default param path and the actual location of the parameters. This reframes the problem from "the daemon can't find its files" to "the daemon is looking in the wrong place."

The fix approach is determined. The assistant proposes generating a minimal config file that overrides the daemon's default param_cache to match the actual param directory. This is more robust than trying to change the daemon's behavior through environment variables, which the daemon ignores.

The need for auto-detection is recognized. Rather than hardcoding a single param path, the script should detect where params actually live — either by checking common locations or by reading the environment. This makes the script portable across different deployment scenarios.

The scope of the fix expands. What began as a simple CLI flag fix (-n → --count) now encompasses a deeper architectural fix: generating a config file for the daemon, exporting FIL_PROOFS_PARAMETER_CACHE for cuzk-bench, and making the script auto-detect the param directory.

The Thinking Process

The assistant's thinking in message [msg 681] is methodical and evidence-driven. It starts with the concrete failure evidence from [msg 675]: the daemon reported "SRS param file not found for Porep32G: /data/zk/params/..." while the script was configured to use /var/tmp/filecoin-proof-parameters. The assistant connects this to the daemon's config default, which it had previously glimpsed in [msg 680] during a grep for param_cache references.

The key insight — that the daemon's config default overrides the env var — is not stated as a guess but as a conclusion drawn from the evidence. The assistant then reads the benchmark script to confirm the current state and to plan the fix. The reading action is not about gathering new information (the script's content is already known) but about establishing a precise baseline for the edit that will follow.

What is notable about this message is what it does not contain. There are no tool calls that modify files, no commands that execute code. It is pure analysis — a pause in the action where the assistant steps back from the immediate failures to understand the systemic issue. This is the kind of reasoning that separates surface-level debugging from genuine root-cause analysis.

The Broader Significance

Message [msg 681] is significant beyond its immediate context because it illustrates a common pattern in complex system integration: the tension between environment variables and configuration files. In the Filecoin proof ecosystem, FIL_PROOFS_PARAMETER_CACHE is the canonical mechanism for parameter discovery. But the cuzk daemon, developed as a separate component with its own configuration conventions, does not honor this mechanism. This kind of inconsistency is inevitable when integrating independently developed systems, and detecting it requires the kind of cross-component tracing that the assistant performs here.

The message also demonstrates the value of reading source code during debugging. The assistant could have tried random fixes — setting the env var differently, moving files around, passing different flags — but instead it traced the daemon's param_cache resolution logic through the codebase. The grep in [msg 680] revealed that the daemon uses param_cache extensively but never reads FIL_PROOFS_PARAMETER_CACHE. This evidence transformed a guess into a confirmed diagnosis.

Finally, the message shows how a single diagnostic step can reshape an entire debugging session. Before this message, the assistant was fixing CLI flags. After this message, the assistant is designing a config-file generation strategy that will ultimately make the benchmark script robust across different deployment environments. The pivot is clean, evidence-based, and decisive.