The Four Words That Unlocked PCE for All Proof Types

In the course of a technical conversation about the CuZK proving engine, a single four-word user message — "Enable on all proofs" — served as the catalyst for a significant multi-step implementation effort. This message, at index 13 in the conversation, is a masterclass in concise technical direction. To understand its weight, one must first understand the context that led to it.

The Backstory: A Discovery of Incompleteness

The conversation began innocuously enough. The user asked for documentation on how to generate Pre-Compiled Constraint Evaluators (PCEs) — a critical optimization in the CuZK GPU-resident SNARK proving engine. PCE works by exploiting the fact that Filecoin's circuits have a fixed R1CS structure; only the witness changes between proofs. By pre-extracting the constraint matrices into CSR (Compressed Sparse Row) format once and reusing them, PCE eliminates the expensive overhead of rebuilding ~130M LinearCombination objects per proof, reducing synthesis time from ~50s to ~35s — a 1.42x speedup.

The assistant initially described three methods for generating PCE: automatic extraction on the first proof, offline generation via a benchmark tool, and disk preloading at startup. The user, displaying healthy skepticism, asked a pointed question: "Are you sure the automatic PCE extraction is actually enabled?"

This question triggered a deep investigation. The assistant dove into the engine code at /tmp/czk/extern/cuzk/cuzk-core/src/engine.rs and discovered a sobering reality. Despite the documentation suggesting that PCE extraction happened automatically for all proof types, the code revealed a different story. The background extraction call sites — at lines 1322, 1529, and 1728 — were all hardcoded to PoRep C2 only. The monolithic path at line 1728 explicitly gated extraction with if let ProofKind::PoRepSealCommit = proof_kind. WinningPoSt, WindowPoSt, and SnapDeals had no extraction path whatsoever.

The assistant's report was stark:

| Proof Type | Auto-extract | Offline tool | Disk preload | |---|---|---|---| | PoRep C2 32G | Yes | Yes | Yes | | WinningPoSt | No | No | Yes (but nothing creates it) | | WindowPoSt | No | No | Yes (but nothing creates it) | | SnapDeals | No | No | Yes (but nothing creates it) |

The infrastructure for loading and using PCE — the OnceLock statics, the disk file naming, the synthesize_with_pce() fast path — was fully wired for all four circuit types. But the extraction path, the code that actually creates the PCE data structure from a circuit, only existed for PoRep.

The Message: "Enable on all proofs"

It is at this precise moment that the user delivers the subject message. The message is terse — just four words — but it carries enormous implied content. The user is not asking a question or requesting analysis. The user is issuing a directive. The reasoning is clear: the infrastructure exists, the optimization is valuable, and there is no principled reason why PoRep should be the sole beneficiary. The user's motivation is practical — they want all 32G proofs to run with PCE acceleration, not just one type.

The message assumes that enabling PCE for all proofs is feasible — that the generic extract_and_cache_pce() function at pipeline.rs:433, which accepts any bellperson::Circuit<Fr>, can handle the circuit constructions for WinningPoSt, WindowPoSt, and SnapDeals. This is a reasonable assumption given the architecture, but it also glosses over significant complexity: each proof type builds its circuit differently, with different parameters, different data sources, and different numbers of partitions.

There is also an implicit assumption that the monolithic synthesis path (the only path that handles non-PoRep proofs) is the right place to wire up extraction. The assistant would later discover that this assumption, while correct for the immediate task, might not be the full story — the user would subsequently ask whether SnapDeals and WindowPoSt should also use partitioned pipelines, revealing a deeper architectural question.

The Implementation Journey

The assistant responded to the directive with immediate action. A todowrite block was created with a structured plan:

Understand how non-PoRep proofs are synthesized in the monolithic path
Understand how each proof type's circuit is constructed
Add extraction functions for WinningPoSt, WindowPoSt, and SnapDeals
Wire them into the engine's monolithic path The assistant read the synthesis functions for each proof type — synthesize_winning_post(), synthesize_window_post(), and synthesize_snap_deals() — to understand how circuits are built. Each function constructs a circuit from request data (vanilla proof bytes, registered proof type, miner ID, randomness, commitment data) and passes it through synthesize_auto(), which already uses PCE if cached. The missing piece was simply that nothing triggered extraction. Three new extraction functions were added to pipeline.rs, each mirroring the circuit construction of its corresponding synthesis function: - extract_and_cache_pce_from_winning_post() — rebuilds the WinningPoSt circuit from vanilla proof bytes, registered proof type, miner ID, and randomness - extract_and_cache_pce_from_window_post() — same pattern for WindowPoSt, additionally taking partition_index - extract_and_cache_pce_from_snap_deals() — rebuilds a single SnapDeals partition circuit (partition 0, since R1CS structure is identical across partitions) All three persist to disk via FIL_PROOFS_PARAMETER_CACHE, just like the PoRep extraction. In engine.rs, the PoRep-only gate at the monolithic synthesis path was replaced with a match on all four ProofKind variants. Each branch spawns a background thread (non-blocking), clones the request data it needs, and logs success or failure as non-fatal — exactly the same pattern as the existing PoRep extraction. The build passed cleanly with cargo check -p cuzk-core, confirming syntactic and type correctness.

The Deeper Question

The user's follow-up — "Isn't Snap/WindowPoSt partitioned same way?" — revealed that the initial implementation, while correct, might not be the optimal approach. The partitioned pipeline for PoRep overlaps synthesis and GPU proving across partitions, reducing wall-clock time by ~43%. If SnapDeals and WindowPoSt are similarly partitioned (SnapDeals has 16 partitions, WindowPoSt has a configurable number), they could benefit from the same overlapping pipeline architecture. The user's initial directive — "Enable on all proofs" — was interpreted as enabling PCE extraction, but the deeper architectural question of enabling partitioned pipelines for all proof types remained open.

This illustrates an important dynamic in the conversation: the user's concise messages pack multiple layers of meaning. "Enable on all proofs" could mean PCE extraction (the immediate context), partitioned pipelines (the deeper optimization), or both. The assistant chose the most straightforward interpretation and delivered working code, but the conversation continued to explore the fuller implications.

What This Message Created

The output knowledge generated by this message is substantial. Three new extraction functions were added to the codebase, each representing a careful reconstruction of circuit-building logic. The engine's monolithic path was generalized from a PoRep-only extraction gate to a proof-type-aware dispatch. The build was verified clean. But perhaps most importantly, the message established a pattern: the user expects parity across proof types, and the assistant should proactively consider whether optimizations applied to one proof type should be extended to all.

The message also created a new branch in the conversation's trajectory. Without it, the assistant would have reported the PoRep-only limitation and perhaps moved on. Instead, the conversation continued into partitioned pipeline analysis, GPU timing breakdowns, and architectural discussions about overlapping synthesis and proving for SnapDeals.

Conclusion

"Enable on all proofs" is a textbook example of an expert user's directive. It is short because the user trusts the assistant to understand the full context: the infrastructure exists, the gap is known, and the fix is well-scoped. It assumes feasibility, assumes the assistant can infer the implementation approach from the existing code patterns, and assumes that the right thing to do is to generalize rather than leave three proof types behind. The message's brevity belies its impact — it set in motion a chain of code changes, architectural investigations, and deeper questions about pipeline design that would occupy the remainder of the conversation.