This is the fifth article in the Exeris Kernel series. The series has been building one coherent architectural picture: article one replaced ThreadLocal with ScopedValue on the context propagation path; article two argued that some layers do not benefit from runtime polymorphism; article three showed where StructuredTaskScope genuinely earns its keep; article four pushed TLS off the heap entirely. This one is about where STS stops being the right tool — and what had to be built instead. The Constraint I Kept Hitting The pressure came from a specific place: I was building the orchestration layer for Exeris Kernel — the part that drives multi-step business processes with compensation and external event wiring. The obvious starting point was an existing enterprise saga framework. I considered Camunda, Axon, and several others in that category, and rejected all of them.…