Status: IN
Error contracts are defined per-module with no cross-cutting convention — payment splits exceptions from return codes, the KV store raises generic exceptions, click aggregation uses boolean returns, and routing collapses all failures to None — making each module boundary an error translation boundary that callers must learn independently.
absence of codebase-wide error convention plus None-return collapse means every module defines its own failure vocabulary
Depends on (SL): error-signaling-lacks-codebase-convention, none-return-collapses-distinct-failure-modes