Session was one of the final services still exposing a Kilo-added runtime-backed Promise facade. That compatibility layer kept Kilo callers and behavior setup coupled to a service-local runtime, and prevented the strict facade ratchet from removing its Session exception.

This removes the Session Promise adapter block while preserving the durable Session.fork recursive child-remap extension. Message and part validation now lives at the service mutation boundary, so direct service consumers retain the validation behavior that previously sat in the deleted wrappers. Effect-native Kilo workflows consume Session.Service directly, while Promise-shaped integration boundaries use the shared application runtime instead of rebuilding a Session-local runtime. Related behavior setup now reaches Session through scoped layers rather than the deleted helpers.

This overlaps with the parallel Question and SessionPrompt facade work in plan-followup, remote-sender, and prompt-queue surfaces. The later-integrated branch must preserve each already-landed service migration. If the open session-export work lands first, its additions in session.ts must be reconciled without restoring the removed facade.

Closes #10722
Part of #10655