fix(domain,application,infrastructure,backend,app-tauri,frontend): Stop demande agent préserve la conversation ouverte — arrêt sans fermeture/clôture du chat, états cohérents après cancel sur les 3 adapters de session, cellule et workstate synchronisés — #343 (QA verte)

frontend/src/adapters/mock/index.ts

@@ -9,6 +9,7 @@ import type {
   AgentDrift,
   AppExitWorkGuardState,
   AgentProfile,
+  CancelAgentChatResult,
   DiagnosticWarning,
   DomainEvent,
   EffortSelection,
@@ -1133,13 +1134,14 @@ export class MockAgentGateway implements AgentGateway {
     }
   }
 
-  async cancelAgentChat(sessionId: string): Promise<void> {
+  async cancelAgentChat(sessionId: string): Promise<CancelAgentChatResult> {
     if (!this.chatScrollback.has(sessionId)) {
       throw {
         code: "NOT_FOUND",
         message: `agent chat session ${sessionId} not found`,
       } as GatewayError;
     }
+    return { sessionId, outcome: "cancelled" };
   }
 
   async reattach(