Segment 15
In this sub-session, the assistant first completed Phase 4 synthesis hot path optimizations by benchmarking and validating Boolean::add_to_lc/sub_from_lc methods, achieving an 8.3% synthesis improvement (55.4s → 50.9s). A full E2E proof revealed a GPU wrapper regression (36.0s vs 34.0s baseline) which was diagnosed as synchronous destructor overhead from freeing ~37 GB of C++ vectors and ~130 GB of Rust Vecs. The fix—moving deallocation to detached threads on both sides—dropped GPU wrapper time to 26.2s and total E2E to 77.2s, a 13.2% improvement over the 88.9s baseline. All Phase 4 changes were committed. The assistant then investigated the user's hypothesis that allocation overhead during synthesis might mirror the deallocation bottleneck. Tracing revealed that a SynthesisCapacityHint API already existed but was never wired up in pipeline callers. After implementing a global hint cache and modifying all six synthesis call sites, rigorous benchmarking showed zero measurable impact (50.65s synthesis time with and without hints), confirming that allocation is amortized by geometric push and parallel computation, and that the synthesis bottleneck is purely computational, reinforcing the need for Phase 5 (PCE).