We introduce noise reachability analysis — a method for determining which physical qubit errors propagate past quantum error correction codes to become logical errors. The engine classifies noise into three source categories (channel, gate, environment) with 12 sub-types, evaluates each against six QEC code families at multiple code distances (720 evaluations per scan), and determines which errors are "reachable" (propagate past the best available correction). We demonstrate automatic noise bias detection, correlated burst noise handling, and noise-aware QEC code selection. The engine recommends optimal codes with 24 source-specific compensating controls beyond code distance increase. Implemented within QCrypton and validated across multiple noise scenarios, the analysis completes in under 2ms.