The Integration Blueprint: Wiring a Remote GPU Proving Daemon into Curio's Task Scheduler

Introduction

In the long and intricate arc of the cuzk proving engine project—spanning dozens of segments and hundreds of messages—message 3446 stands as a singular moment of consolidation. It is not a moment of execution, but of reflection: a comprehensive status report, an architectural summary, and a forward-looking TODO list all rolled into one. Written by the AI assistant after completing the initial round of integration work that wired the cuzk proving daemon into Curio's task scheduler, this message serves as a checkpoint that documents what was built, what was learned, and what remains to be done.

The message arrives at a pivotal juncture. The cuzk proving daemon—a persistent, GPU-resident SNARK proving engine—has been under development across twelve prior phases, each tackling a different aspect of the Groth16 proof generation pipeline for Filecoin's Proof-of-Replication (PoRep) and related proofs. Now, the work shifts from building the engine itself to integrating it into Curio, the Filecoin storage provider software that orchestrates proof generation tasks. Message 3446 is the assistant's synthesis of this integration effort: a document that captures the design rationale, the implementation decisions, the discoveries made along the way, and the remaining work.

This article examines message 3446 in depth, exploring why it was written, what decisions it encodes, what assumptions it makes, and what knowledge it both consumes and produces. We will see that this message is not merely a progress report—it is an architectural artifact that reveals the thinking behind a complex system integration, the tradeoffs involved in delegating GPU computation to a remote daemon, and the pragmatic realities of working within a large existing codebase.

The Context: From Engine to Integration

To understand message 3446, one must first understand the journey that preceded it. The cuzk project began as an investigation into the SUPRASEAL_C2 Groth16 proof generation pipeline for Filecoin PoRep, a computation with a staggering ~200 GiB peak memory footprint. Over the course of earlier segments, the assistant mapped the entire call chain from Curio's Go task layer through Rust FFI into C++/CUDA kernels, identified nine structural bottlenecks, and proposed three optimization strategies: Sequential Partition Synthesis to reduce peak memory, a Persistent Prover Daemon to eliminate SRS loading overhead, and Cross-Sector Batching to improve throughput.

Subsequent phases implemented these ideas. Phase 11 introduced memory-bandwidth interventions. Phase 12 implemented a split GPU proving API that decoupled the GPU worker's critical path from CPU post-processing, followed by memory backpressure mechanisms and a comprehensive low-memory benchmark sweep. By the end of Phase 12, the cuzk daemon was a functioning, optimized proving engine—but it existed as a standalone binary, disconnected from Curio's task orchestration.

Message 3446 sits at the boundary between Phase 12 and Phase 13. The engine exists. Now it must be integrated. The message documents the first wave of this integration: adding configuration, generating protobuf stubs, creating a gRPC client wrapper, writing new SealCalls methods that split vanilla proof generation from SNARK computation, and modifying three task types (PoRep, SnapDeals, and PSProve) to optionally delegate their GPU work to cuzk.

Why This Message Was Written

The most immediate question about message 3446 is: why was it written at all? It is not a response to a user prompt—the preceding user message (index 3445) is empty, and the assistant's previous message (index 3444) was a brief confirmation that an edit had been applied. Message 3446 appears to be the assistant's own initiative: a self-generated status update and planning document.

This is a distinctive pattern in the opencode session. The assistant periodically produces these comprehensive summaries, especially after completing a significant body of work. The motivation is twofold. First, the assistant is maintaining a working context across a very long conversation (over 3,400 messages by this point). By periodically consolidating what has been done, what has been learned, and what remains, the assistant ensures that both it and the user share a common understanding of the project state. Second, the message serves as a planning tool: by explicitly listing the completed items and the remaining TODOs, the assistant creates a structured agenda for the next round of work.

The message's structure reflects this dual purpose. It begins with a Goal section that restates the integration's purpose and scope, ensuring alignment. The Instructions section codifies the design principles that guided the implementation. The Discoveries section captures unexpected findings—the inverted logic of enableRemoteProofs between PoRep and Snap tasks, the CGO build limitations, the need to thread cuzkClient through three levels of function calls in PSProve. The Accomplished section provides a detailed inventory of what was completed, organized by file and annotated with build status. The TODO section prioritizes the remaining work. The Relevant files section maps the entire integration surface area.

In essence, message 3446 is the assistant's way of saying: "Here is where we are. Here is what we know. Here is what comes next." It is a metacognitive artifact—a snapshot of the assistant's own understanding of the integration at a particular moment in time.

The Architectural Decisions

Message 3446 encodes several critical architectural decisions that shape the entire integration. These decisions are presented as instructions or discoveries, but they represent choices that were made—either explicitly during the implementation or implicitly through the assistant's reading of the existing code.

Backpressure via gRPC Polling

The most fundamental decision is how to handle resource accounting. In Curio's harmony scheduler, tasks declare their resource requirements (GPU count, RAM) in TypeDetails(), and the scheduler uses these to decide how many tasks to run concurrently. When cuzk is enabled, however, the GPU work happens on a remote machine. Local resource accounting becomes meaningless—and worse, it would prevent the scheduler from running tasks that don't actually consume local GPU resources.

The assistant's solution, documented in the Instructions section, is to "zero out GPU and large RAM in TypeDetails()" and instead use CanAccept() to query the cuzk daemon's pending queue via GetStatus. This is a clean architectural decision: it replaces a static resource budget with a dynamic backpressure mechanism. The local machine says "I have infinite capacity for GPU work" (by zeroing the resource requirements), but then individually gates each task acceptance on the daemon's actual queue depth. This prevents overloading the daemon while allowing the scheduler to freely dispatch tasks that will be handled remotely.

The decision reveals a deep understanding of both the harmony scheduler's internals and the operational reality of a remote proving service. Static resource accounting works when the resource is local and dedicated. For a shared remote service, dynamic backpressure is essential.

Splitting Vanilla Proof Generation from SNARK Computation

A second key decision is where to draw the boundary between local and remote computation. The assistant's analysis of PoRepSnark (documented in the Discoveries section) reveals that the existing proof pipeline does two things: (1) GeneratePoRepVanillaProof, which runs on CPU and requires access to sector data on disk, and (2) SealCommitPhase2, which runs the GPU SNARK computation. For cuzk integration, step 1 stays local and step 2 goes to the remote daemon.

This split is not merely a technical detail—it is an architectural principle. The vanilla proof generation requires direct access to the sector's sealed and unsealed data files, which are stored on the local machine's disks. Moving this step to the remote daemon would require transferring potentially gigabytes of sector data over the network, which is impractical. By keeping vanilla proof generation local and sending only the compact vanilla proof (a JSON-serialized byte array) to the daemon, the integration minimizes network bandwidth while still offloading the expensive GPU computation.

The same pattern applies to SnapDeals: ReadSnapVanillaProof (local, reads a pre-computed proof from disk) plus GenerateUpdateProofWithVanilla (GPU, now remote). The assistant's new PoRepSnarkCuzk and ProveUpdateCuzk methods in lib/ffi/cuzk_funcs.go implement this split, generating the vanilla proof locally and then sending it to cuzk via gRPC.

Reusing Existing Task Patterns

A third decision, visible in the Discoveries section, is to reuse the existing enableRemoteProofs fields that already existed in the PoRep and Snap tasks. The assistant discovered that PoRep uses cfg.Subsystems.EnablePoRepProof (where false means "proofs done elsewhere, reject locally") while Snap uses cfg.Subsystems.EnableRemoteProofs (where true means "reject locally"). Rather than introducing new configuration fields for cuzk, the assistant layers cuzk on top of these existing patterns: when cuzk is enabled AND the existing remote-proofs flag indicates that local proving is allowed, the task uses cuzk instead of the local ffiselect library.

This decision minimizes configuration surface area and maintains backward compatibility. Storage providers who already use the remote-proofs mechanism can add cuzk without changing their existing workflow. The assistant correctly identifies that the two tasks have inverted logic for their enableRemoteProofs fields—a subtlety that could easily cause bugs if not carefully documented.

Assumptions Embedded in the Message

Message 3446 makes several assumptions, some explicit and some implicit. Understanding these assumptions is crucial for evaluating the soundness of the integration.

The cuzk Daemon Is Independently Running

The most fundamental assumption is that the cuzk daemon is a separate process that Curio connects to via gRPC. The Instructions section states: "The cuzk daemon stays independent (not embedded in Curio) — Curio connects to it via gRPC (unix socket or TCP)." This assumption shapes the entire integration: the gRPC client, the configuration for the daemon address, the polling-based backpressure, and the timeout settings. If the daemon were embedded, the integration would look completely different—shared memory, direct function calls, and different resource accounting.

This assumption is justified by the earlier phases of the project, which designed cuzk as a standalone daemon. But it carries implications: the daemon must be deployed, configured, monitored, and kept running independently of Curio. The integration assumes this operational burden is acceptable.

The Network Is Reliable and Fast

The integration assumes that gRPC calls to the cuzk daemon are fast enough for CanAccept() to poll the queue status without introducing unacceptable latency. The CanAccept() method is called frequently by the harmony scheduler as it evaluates tasks. If each call requires a round-trip to the daemon, and the daemon is on a remote machine with network latency, this could become a bottleneck.

The assistant does not address this concern in message 3446, though the ProveTimeout default of 30 minutes suggests an awareness that proof computation itself is long-lived. The GetStatus call, however, is expected to be lightweight—a simple queue depth query. The assumption is that this is fast enough to be called from CanAccept() without issue.

The CGO/FVM Build Issues Are Pre-Existing

Throughout the implementation, the assistant encounters CGO/FVM compilation errors when building lib/ffi/. The Discoveries section notes: "This machine cannot fully compile lib/ffi/ due to missing FVM CGO headers." The assistant assumes these errors are pre-existing and not introduced by the new code, using go vet (filtering out CGO errors) as a substitute for full compilation.

This is a pragmatic assumption—the development environment lacks certain headers, but the code is structurally correct. However, it means the integration has not been fully tested end-to-end. The assistant is relying on type checking and static analysis rather than runtime verification.

Mistakes and Incomplete Work

Message 3446 is honest about its limitations. The TODO section explicitly lists what remains unfinished, and the Discoveries section reveals several stumbles along the way.

The PSProve TypeDetails/CanAccept Gap

The assistant notes that PSProve's TypeDetails() and CanAccept() have not yet been updated for cuzk. While the Do() method and the compute functions have been modified to support cuzk, the resource accounting and backpressure for PSProve tasks still use the old local-GPU logic. This is an incomplete integration—if cuzk is enabled, PSProve tasks would attempt to use the remote daemon in Do(), but the scheduler would still be allocating local GPU resources for them, potentially causing resource conflicts.

The assistant flags this as the first TODO item, indicating awareness that it must be addressed before the integration is complete.

Broken Constructor Call Sites

A more immediate problem is that the constructor call sites in cmd/curio/tasks/tasks.go are now broken. The assistant added a cuzkClient parameter to NewPoRepTask, NewProveTask (snap), and NewTaskProvideSnark, but the code that calls these constructors has not been updated. This means the code does not compile in its current state—a fact the assistant acknowledges in the TODO section.

This is a deliberate tradeoff: the assistant chose to modify the task implementations first, knowing that the call sites would break, and planned to fix them in the next round. The message serves as a reminder of what needs to be done, ensuring the user (and the assistant itself) doesn't forget to wire up the cuzk client initialization.

Proto Generation Stumbles

The Discoveries section briefly mentions that proto code generation required the M flag to set the Go package path, and that the initial attempt created a nested directory that had to be flattened. These are minor stumbles, but they illustrate the iterative nature of the implementation. The assistant tried a straightforward protoc invocation, hit an error about missing go_package, added the M flag, then discovered the output was nested in an unexpected directory structure, and had to move files manually. Each iteration taught the assistant something about the toolchain, and these learnings are captured in the Discoveries section for future reference.

Input Knowledge Required

To fully understand message 3446, a reader needs familiarity with several domains:

Curio's harmony task framework: The message references TaskInterface, TaskTypeDetails, CanAccept, Do, and the scheduling loop. Understanding how harmony decides which tasks to run, how it accounts for resources, and how CanAccept gates task acceptance is essential for grasping the integration's architecture.

Filecoin proof types: The message discusses PoRep C2 (Proof-of-Replication, phase 2), SnapDeals Prove (UpdateProve for sector updates), and PSProve (proofshare for delegated proving). Each has a different proof generation pipeline and different existing remote-proofs configuration.

The cuzk daemon architecture: The message assumes the reader knows that cuzk is a persistent GPU-resident SNARK proving engine, that it communicates via gRPC, and that it exposes Prove, GetStatus, and other RPCs defined in the protobuf at extern/cuzk/cuzk-proto/proto/cuzk/v1/proving.proto.

Go protobuf code generation: The message describes using protoc with the M flag to set Go package paths, and the resulting file structure. Understanding protobuf code generation conventions helps make sense of the steps described.

The existing proof pipeline: The message references PoRepSnark, SealCommitPhase2, GeneratePoRepVanillaProof, ProveUpdate, ReadSnapVanillaProof, and GenerateUpdateProofWithVanilla. These are functions in the Filecoin FFI library that the integration is wrapping.

Output Knowledge Created

Message 3446 creates several kinds of knowledge that serve as inputs for subsequent work:

A complete file inventory: The message lists every file created and modified, organized by status (created, modified, needs modification, read for reference). This serves as a checklist for the next phase of work and as documentation for anyone reviewing the changes.

An architectural map: The message documents how the integration works at a conceptual level: configuration → gRPC client → SealCalls methods → task modifications. Each layer is described with its purpose and its status.

A prioritized TODO list: The five remaining items are ordered by apparent priority. PSProve TypeDetails/CanAccept comes first, followed by wiring the cuzk client initialization (which is blocking compilation), then build verification, documentation, and a consideration question about PoSt tasks.

Design rationale documentation: The Goal and Instructions sections capture why decisions were made, not just what was done. This is valuable for future maintainers who need to understand the reasoning behind the integration's architecture.

Operational notes: The Discoveries section captures practical knowledge that would otherwise be lost: the inverted logic of enableRemoteProofs between PoRep and Snap, the CGO build limitations, the need to thread cuzkClient through multiple function layers in PSProve. These are the kinds of details that are expensive to rediscover.

The Thinking Process Visible in the Message

While message 3446 is primarily a summary document, it reveals the assistant's thinking process in several ways. The Discoveries section is particularly revealing—it shows the assistant actively learning from the codebase as it works.

The discovery about enableRemoteProofs is a good example. The assistant read the PoRep task and found cfg.Subsystems.EnablePoRepProof, then read the Snap task and found cfg.Subsystems.EnableRemoteProofs—a different field with inverted logic. The assistant not only notes this difference but immediately understands its implications: "When cuzk is enabled AND enableRemoteProofs == true, we use cuzk instead of local ffiselect" for PoRep, while for Snap, "When true, CanAccept rejects locally." This is not just data collection—it is active reasoning about how the existing patterns interact with the new cuzk integration.

Similarly, the discovery about PSProve's function structure reveals the assistant tracing through the call graph: "Uses package-level computeProof/computePoRep/computeSnap functions that directly call ffiselect.FFISelect — needed to thread cuzkClient parameter through all three functions." The assistant recognized that PSProve's architecture was different from PoRep and Snap (which use methods on the SealCalls struct), requiring a different approach to threading the cuzk client.

The CGO build discovery is another window into the assistant's thinking. Rather than treating the compilation errors as a blocker, the assistant diagnosed them as pre-existing (missing FVM headers) and adapted the verification strategy: "use go vet filtering out CGO errors to verify Go source correctness." This is a pragmatic response to an environmental constraint, showing the assistant's ability to distinguish between problems with its own code and problems with the build environment.

Conclusion

Message 3446 is far more than a status update. It is an architectural document, a learning journal, a planning tool, and a coordination artifact all in one. It captures the state of a complex integration at a specific moment, documenting not just what was done but why it was done, what was learned in the process, and what remains to be accomplished.

The message's value lies in its comprehensiveness and its honesty. It celebrates completed work (seven items checked off with ✅ markers) while openly acknowledging gaps (the TODO list, the broken call sites, the CGO build limitations). It captures design decisions with enough context that a future reader can understand the reasoning. It documents operational discoveries that would otherwise be lost.

For anyone studying the cuzk project, message 3446 is an essential reference. It maps the entire integration surface area across configuration, protobuf generation, gRPC client, FFI methods, and three task types. It explains the architectural principles—backpressure via polling, splitting vanilla from SNARK, reusing existing patterns—that guided the implementation. And it sets the stage for the next phase of work, which will wire up the cuzk client initialization, complete the PSProve integration, and commit the changes.

In the broader arc of the opencode session, message 3446 represents a moment of consolidation before a push toward completion. It is the assistant taking stock, ensuring that both it and the user share a clear picture of the integration's state, and laying out a structured plan for finishing the work. It is, in essence, the assistant thinking aloud—and that thinking, captured in a single message, is what makes this document worth studying.