In general, to fix a "missed opportunity to use Where" in a foreach loop that immediately tests each element with an if and either continues or breaks, you replace the loop with a LINQ query that directly expresses the predicate, then act on the filtered result(s). This usually reduces nesting and makes it obvious you are searching or filtering, rather than performing arbitrary per-element logic.

For this specific case, the loop is only interested in whether there exists any aggregate configuration whose Catalogue is non-null and IsInternalDataset. On finding the first such configuration, it sets task.CrashMessage and task.State and stops iterating. The clearest equivalent using LINQ is to obtain the first offending configuration via FirstOrDefault, then if that result is non-null, set CrashMessage/State. We already have using System.Linq; at the top, so no new imports are needed. The behavior remains unchanged: there is at most one place where CrashMessage/State are set in this block, and enumeration stops as soon as the first problematic configuration is found.

Concretely, in Rdmp.Core/CohortCreation/Execution/CohortCompiler.cs, replace the foreach block at lines 325–333 with code that calls cac.GetAggregateConfigurations().FirstOrDefault(...) using the same predicate (ac => ac.Catalogue != null && ac.Catalogue.IsInternalDataset). If a matching configuration is found, construct the same ArgumentException using that configuration’s Catalogue.Name and set task.State = CompilationState.Crashed;. No additional methods or fields are required.