Merge latest main and preserve teacher upgrade safeguards

electron/coding-teacher/service.ts

@@ -479,11 +479,13 @@ export class CodingTeacherService {
         const previous = topic.requests.at(-1);
         const reuse = previous && !previous.origin && previous.projectId === scope.projectId
           && previous.sourceConversationId === input.sourceConversationId
+          && previous.presentation === 'reply-v1'
           && previous.teacherVersion === selected.version && previous.runtimeThreadId;
         newConversationSegment = !reuse;
         // Yuxi binds both project and Pi source to a thread. Preserve its native
         // summary middleware within a segment; explicitly carry bounded public
-        // history only when a new scope/release starts another segment.
+        // history only when a new scope, release, or reply protocol starts another
+        // segment. Older checkpoints may still contain retired component instructions.
         topic.conversation!.runtimeThreadId = reuse || randomUUID();
         topic.conversation!.segmentTurns = reuse ? topic.conversation!.segmentTurns + 1 : 1;
       }