The Anatomy of a Deadlock: Tracing a Distributed Proving System's Fatal Embrace

In the high-stakes world of Filecoin proof generation, where GPU workers race against time to compute zk-SNARKs for the ProofShare challenge market, a deadlock is more than a nuisance—it is a silent killer of revenue, a black hole that swallows proving capacity whole. Message 1911 captures a pivotal moment in the debugging of precisely such a deadlock: the assistant, having received confirmation of the bug from the user, pivots from high-level diagnosis to deep code exploration. This message is the bridge between "we know something is broken" and "we know exactly how to fix it." It is a study in systematic investigation, where the assistant reads four critical source files to trace the exact contours of a deadlock that had been locking up production nodes.

The Deadlock Described

The bug, as reported by the user in [msg 1907], was a textbook distributed systems deadlock with a cruel feedback loop. The TaskRequestProofs system in the Curio proving node works by polling a remote ProofShare service for available work "asks"—essentially, challenges that need proofs. The system calls CreateWorkAsk to claim these slots, and only after all slots are claimed does it insert entries into a local proofshare_queue table. Proving tasks then pick up work from this queue, compute proofs, and submit them back, which frees slots for more work asks.

The problem emerged when the ProofShare service began returning HTTP 429 (TooManyRequests) responses. The service was rate-limiting the node, allowing only one or two work asks to succeed before returning 429 for subsequent attempts. But CreateWorkAsk was written to retry indefinitely on any HTTP error, polling the service forever until it got a non-error response. This created a perfect deadlock: the node had taken one or two asks but couldn't complete the remaining ones because CreateWorkAsk was stuck retrying. Since the code wouldn't insert into proofshare_queue until all work asks completed, no entries ever appeared in the queue. Without queue entries, no proving tasks could run. Without proving tasks completing, no slots could be freed. And without freed slots, no new work asks could succeed. The system was locked in a fatal embrace, unable to make progress.

The user confirmed this diagnosis in [msg 1910]: restarting a locked-up node caused PSProve tasks to immediately appear because the restart triggered a fresh poll of the service state, which populated the queue before the rate-limiting could re-assert itself.

The Exploratory Pivot

Message 1911 is the assistant's response to this confirmation. The assistant had already explored the codebase in [msg 1909] via a subagent task, producing a comprehensive analysis of the TaskRequestProofs system. But now, with the deadlock confirmed, the assistant needed to move from general understanding to precise fix design. The message begins with the assistant's reasoning:

The user has confirmed the deadlock scenario. Let me now read the key files in detail to understand the exact code paths and design a solid fix. I'm in plan mode, so I can only read/search, not edit.

This framing is crucial. The assistant is operating under a constraint—it is in "plan mode," meaning it can read and search but cannot make edits. This is a deliberate architectural choice in the opencode system: before any changes are made, the assistant must fully understand the problem and design the solution. The message is therefore entirely diagnostic, not prescriptive. It is the calm before the storm of code changes.

The Four Files

The assistant reads four files in this message, each chosen for a specific reason:

/tmp/czk/tasks/proofshare/task_request.go: This is the main file containing the TaskRequestProofs struct and its core logic. It contains the poll loop that calls CreateWorkAsk, the logic that decides when to insert into proofshare_queue, and the overall orchestration of the request phase. Understanding this file is essential to see where the deadlock occurs—specifically, where the code blocks waiting for all work asks to complete before proceeding to the queue insertion step.

/tmp/czk/lib/proofsvc/provictl.go: This file contains the CreateWorkAsk function itself, along with the HTTP client logic for communicating with the ProofShare service. The assistant needs to see exactly how HTTP errors are handled—whether 429 is treated as a retryable error or something that should cause an early return. The fix will likely involve changing this behavior, so understanding the current implementation is critical.

/tmp/czk/tasks/proofshare/task_prove.go: This file contains the proving task logic that picks up work from proofshare_queue and computes proofs. It represents the other end of the deadlock chain: if no entries appear in the queue, this code never runs, and slots never free up. The assistant needs to understand how this side works to ensure the fix doesn't break the overall pipeline.

/tmp/czk/tasks/proofshare/task_submit.go: This file handles the submission of completed proofs back to the ProofShare service. It also contains the logic for cleaning up completed queue entries—or rather, the lack thereof. The user mentioned a secondary issue about proofshare_queue never being cleaned up, causing SELECT queries to grow expensive over time. This file is where any cleanup routine would be added.

The Thinking Process

The assistant's reasoning in this message reveals a structured approach to debugging distributed systems. The first step is always to confirm the bug exists and understand its symptoms—the user did this by restarting a locked node and observing that PSProve tasks immediately appeared. The second step is to trace the causal chain: HTTP 429 → CreateWorkAsk retries forever → queue never populated → prove tasks never run → slots never freed → deadlock. The third step, which this message represents, is to read the exact code to identify the specific lines and control flows that need to change.

The assistant is not just reading files randomly; it is reading with intent. Each file corresponds to a link in the deadlock chain. task_request.go is where the deadlock manifests (the blocking wait). provictl.go is where the root cause lives (the infinite retry on 429). task_prove.go and task_submit.go are the downstream components that must continue to work correctly after the fix.

Assumptions and Knowledge

This message rests on several layers of domain knowledge. The reader must understand what a "work ask" is in the ProofShare context—a claim on a challenge that needs a proof. They must understand HTTP 429 as a rate-limiting signal that should cause the caller to back off, not retry indefinitely. They must understand the harmony task framework in Curio, where tasks are polled, executed, and completed in a loop. And they must understand the queue-based architecture where work flows from service → queue → prove task → submit task → service.

The assistant assumes that the deadlock chain is correctly understood—that the blocking point is indeed the CreateWorkAsk retry loop, and that making it non-blocking (or returning early on 429) will break the deadlock. This assumption is well-supported by the user's confirmation and the assistant's earlier analysis.

The Significance of This Message

Message 1911 is significant because it represents the moment when debugging transitions into design. The assistant has the user's confirmation, the subagent's analysis, and now the raw source code. Everything needed to design the fix is being assembled. The message itself produces no output beyond the file contents—it is purely consumptive—but it is the necessary precursor to the productive work that follows.

In the broader narrative of segment 13, this message is the turning point. The user reported the deadlock in [msg 1907]. The assistant explored the codebase in [msg 1908] and [msg 1909]. The user confirmed the deadlock in [msg 1910]. And now, in [msg 1911], the assistant reads the exact files that will be edited in subsequent messages. The fix that emerges—making CreateWorkAsk return a sentinel ErrTooManyRequests immediately on 429, allowing the poll loop to continue with partial progress—is a direct consequence of the understanding gained in this message.

Conclusion

Message 1911 is a study in disciplined debugging. It shows an assistant that does not rush to edit code without first understanding it, that reads with purpose and intent, and that uses the constraint of "plan mode" to force a thorough exploration before any changes are made. The deadlock it investigates is a classic distributed systems failure mode, and the methodical approach to tracing its cause is a model for how to debug such systems. By the end of this message, the assistant has everything it needs: the confirmed bug, the causal chain, and the exact source code of every component involved. The fix is now a matter of engineering, not discovery.