fix(cpu_reference): avoid debug-build overflow in mask isolation#116
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`mask & (-(mask as i32)) as u32` panics with "negate with overflow" in debug builds when `mask` has bit 31 set (negating i32::MIN). Release builds wrap silently. Use `mask.wrapping_neg()` so the lowest-set-bit isolation works identically in debug and release, making `cosim --check-with-cpu` runnable under debug builds. Co-developed-by: Claude Code v2.1.168 (claude-opus-4-8)
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Both PRs merged. Sync handoff to final state: backend-owned schedule (edge_ops_mut), P2/P3 merged in the plan, JTAG on xlarge + 40/45min timeout (validated 32.0min), amendment date refs. Co-developed-by: Claude Code v2.1.168 (claude-opus-4-8)
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What
cpu_reference::simulate_block_v1(and_xprop) isolate the lowest setbit of
maskviamask & (-(mask as i32)) as u32. Whenmaskhas bit31 set,
-(i32::MIN)overflows and panics in debug builds("negate with overflow"); release builds wrap silently, masking the bug.
Fix
Use
mask & mask.wrapping_neg()— same two's-complement lowest-set-bitisolation, but defined for all inputs. Behaviour is identical in release;
debug builds no longer panic, so
cosim --check-with-cpuis now runnableunder debug builds.
Carry-forward item flagged in #115 / the backend-alignment handoff.