fix: chat session reliability, cost, and hygiene (empty-response guard, tool truncation, delete, titles)

- Empty/refusal responses retried once, then surfaced as errors instead of silent blanks
- Chinese refusal boilerplate detected via denylist + non-ASCII heuristic
- Bulk-tool preference added to SOUL.md (list_lxcs over per-entity get_lxc_state)
- Tool results truncated to 4KB on persist; get_state_snapshot filters null-state entities
- Session delete (DELETE /sessions/{id} + confirm-on-second-click UI)
- Session titles auto-generated from assistant answer instead of raw user message

cmd/nomos/main.go

@@ -186,6 +186,15 @@ func handleChat(w http.ResponseWriter, r *http.Request, a *agent, st *store) {
 		"tool_calls": toolCalls,
 	})
 	st.saveMessage(ctx, sessionID, "assistant", assistantMsg)
+
+	// Generate a meaningful title from the assistant's first answer
+	// instead of reusing the raw user message for every session.
+	if finalText != "" && sessionID != "ephemeral" {
+		title := truncate(finalText, 80)
+		if title != "" {
+			st.updateSessionTitle(ctx, sessionID, title)
+		}
+	}
 }
 
 func handleSessionsList(w http.ResponseWriter, r *http.Request, st *store) {
@@ -220,13 +229,26 @@ func handleSessionDetail(w http.ResponseWriter, r *http.Request, st *store) {
 		return
 	}
 
-	messages, err := st.getMessages(r.Context(), id)
-	if err != nil {
-		http.Error(w, err.Error(), 500)
-		return
+	switch r.Method {
+	case http.MethodDelete:
+		if err := st.deleteSession(r.Context(), id); err != nil {
+			http.Error(w, err.Error(), 500)
+			return
+		}
+		w.WriteHeader(204)
+
+	case http.MethodGet:
+		messages, err := st.getMessages(r.Context(), id)
+		if err != nil {
+			http.Error(w, err.Error(), 500)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(map[string]any{"session_id": id, "messages": messages})
+
+	default:
+		http.Error(w, "method not allowed", 405)
 	}
-	w.Header().Set("Content-Type", "application/json")
-	json.NewEncoder(w).Encode(map[string]any{"session_id": id, "messages": messages})
 }
 
 func handleQuery(w http.ResponseWriter, r *http.Request, client *mcpClient, agentSlug, mcpURL string) {