Chunk 20.1

In this chunk, the assistant implemented a critical fix for the partition scheduling order. The previous design spawned all partitions from all pipelines as independent tokio tasks that raced on `budget.acquire()`, causing partitions to be processed in random order. This meant nearly-finished pipelines could stall waiting for GPU proving while other pipelines had no synthesis work left. The fix replaces the per-partition `tokio::spawn` pattern with a shared ordered `mpsc` channel: partitions are enqueued in FIFO order (earlier pipelines first, lower partition indices first), and a pool of synthesis workers pulls from the channel sequentially. This ensures partitions are processed in a predictable, efficient order that minimizes gaps in synthesis work. The assistant also continued debugging the `synth_max` display issue. After building and extracting the new binary from Docker, uploading to the test machine revealed overlay filesystem quirks: the container's overlay FS cached the old binary in a lower layer, causing `cp` and even `scp` to `/usr/local/bin` to silently serve the stale version. The workaround was deploying to `/data/cuzk-ordered` (a path not present in any lower layer). Once running, the new binary still showed `synth: 0/4` instead of the expected `/44`, indicating the `synth_max` fix may not have been included in the build or the config override was still taking precedence—this remained unresolved at the chunk's end.

Order from Chaos: Fixing Partition Scheduling and Battling Overlay Filesystems in the CuZK Proving Engine 2457 words

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