Chunk 26.0

In this chunk, the assistant completed wiring the synthesis throughput cap into the PI pacer (adding `synth_completion_count`, updating all four `pacer.update()` call sites, and adding synth rate info to the periodic status log), then built and deployed the binary as `/data/cuzk-synthcap1`. After deployment, the user identified that the initial GPU rate calibration was measuring pipeline fill time (47s) instead of actual GPU processing time (~1s), causing the EMA to drag down painfully slowly. The assistant attempted to fix this by skipping the first GPU completion and only updating the GPU rate when `waiting > 0`, but the user pointed out this approach is fundamentally flawed with two interleaved GPU workers — both workers can be actively processing with an empty queue, so queue depth doesn't reflect GPU busyness. The assistant pivoted to measuring actual GPU processing duration directly from GPU workers via a shared `AtomicU64`, computing the effective dispatch interval as `ema_gpu_processing / num_workers`, which is immune to both pipeline fill and idle time contamination. This was deployed as `/data/cuzk-synthcap2`. However, the user reported the system was still collapsing — the synthesis throughput cap was creating a self-reinforcing vicious cycle: slow dispatch → fewer concurrent syntheses → slower synthesis throughput → tighter cap → even slower dispatch. The assistant analyzed the logs and identified three root problems: the synth cap creates a collapse loop, there's no re-bootstrap when the pipeline drains between batches, and the 200ms bootstrap spacing floods the pinned memory pool with concurrent `cudaHostAlloc` calls that stall the GPU. The assistant then rewrote the DispatchPacer to remove the synthesis throughput cap entirely, add re-bootstrap detection (re-entering bootstrap when `ema_waiting < 1` with no active bootstrap), and slow bootstrap to 3s for initial warmup or `max(2s, gpu_eff)` for re-bootstrap, letting the PI controller and budget backpressure naturally balance GPU and synthesis rates.

The Arc of Discovery: How a Synthesis Throughput Cap Was Wired, Deployed, and Ultimately Abandoned 3108 words

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