Analyze the security of a proposed Key Encapsulation Mechanism (KEM) based on the Learning with Errors (LWE) problem over a polynomial ring (RLWE). The scheme claims IND-CCA2 security. Your task is to: 1) Identify the specific hardness problem the security reduction relies on. 2) Critique the tightness of the security reduction—specifically, estimate the loss in the security parameter during the reduction from the scheme to the hardness problem. 3) Propose a potential side-channel attack vector related to the decoding process (e.g., failure probability analysis) and suggest a concrete countermeasure to mitigate it.