diff --git a/pkg/agent/loop.go b/pkg/agent/loop.go
index 263eeb4dd..a4a56b2f6 100644
--- a/pkg/agent/loop.go
+++ b/pkg/agent/loop.go
@@ -1133,11 +1133,28 @@ func (al *AgentLoop) runLLMIteration(
 			// Save tool result message to session
 			agent.Sessions.AddFullMessage(opts.SessionKey, toolResultMsg)
 		}
+
+		// If this round only executed message tool calls, stop the loop here.
+		// This prevents "ack-on-ack" loops where the model keeps calling message.
+		if areAllToolCallsMessage(normalizedToolCalls) {
+			break
+		}
 	}
 
 	return finalContent, iteration, nil
 }
 
+func areAllToolCallsMessage(calls []providers.ToolCall) bool {
+	if len(calls) == 0 {
+		return false
+	}
+	for _, tc := range calls {
+		if tc.Name != "message" {
+			return false
+		}
+	}
+	return true
+}
 // maybeSummarize triggers summarization if the session history exceeds thresholds.
 func (al *AgentLoop) maybeSummarize(agent *AgentInstance, sessionKey, channel, chatID string) {
 	newHistory := agent.Sessions.GetHistory(sessionKey)
diff --git a/pkg/agent/loop_test.go b/pkg/agent/loop_test.go
index 4ab6b4542..fd7bd7bb4 100644
--- a/pkg/agent/loop_test.go
+++ b/pkg/agent/loop_test.go
@@ -323,6 +323,39 @@ func (m *simpleMockProvider) GetDefaultModel() string {
 	return "mock-model"
 }
 
+type messageOnlyLoopProvider struct {
+	callCount int
+}
+
+func (m *messageOnlyLoopProvider) Chat(
+	ctx context.Context,
+	messages []providers.Message,
+	tools []providers.ToolDefinition,
+	model string,
+	opts map[string]any,
+) (*providers.LLMResponse, error) {
+	m.callCount++
+	return &providers.LLMResponse{
+		ToolCalls: []providers.ToolCall{
+			{
+				ID:   fmt.Sprintf("tc-%d", m.callCount),
+				Name: "message",
+				Arguments: map[string]any{
+					"content": "Context compressed",
+				},
+				Function: &providers.FunctionCall{
+					Name:      "message",
+					Arguments: `{"content":"Context compressed"}`,
+				},
+			},
+		},
+	}, nil
+}
+
+func (m *messageOnlyLoopProvider) GetDefaultModel() string {
+	return "mock-message-only-model"
+}
+
 // mockCustomTool is a simple mock tool for registration testing
 type mockCustomTool struct{}
 
@@ -448,6 +481,61 @@ func TestToolResult_UserFacingToolDoesSendMessage(t *testing.T) {
 	}
 }
 
+func TestRunLLMIteration_MessageOnlyToolCallsStopAfterOneRound(t *testing.T) {
+	tmpDir, err := os.MkdirTemp("", "agent-test-*")
+	if err != nil {
+		t.Fatalf("Failed to create temp dir: %v", err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	cfg := &config.Config{
+		Agents: config.AgentsConfig{
+			Defaults: config.AgentDefaults{
+				Workspace:         tmpDir,
+				Model:             "test-model",
+				MaxTokens:         4096,
+				MaxToolIterations: 10,
+			},
+		},
+	}
+
+	msgBus := bus.NewMessageBus()
+	provider := &messageOnlyLoopProvider{}
+	al := NewAgentLoop(cfg, msgBus, provider)
+	agent := al.registry.GetDefaultAgent()
+	if agent == nil {
+		t.Fatal("No default agent found")
+	}
+
+	al.beginRoundForMessageTool(agent)
+	al.updateToolContexts(agent, "telegram", "chat-1")
+
+	_, iteration, err := al.runLLMIteration(
+		context.Background(),
+		agent,
+		[]providers.Message{
+			{Role: "system", Content: "test system prompt"},
+			{Role: "user", Content: "压缩上下文"},
+		},
+		processOptions{
+			SessionKey:   "test-session",
+			Channel:      "telegram",
+			ChatID:       "chat-1",
+			SendResponse: false,
+		},
+	)
+	if err != nil {
+		t.Fatalf("runLLMIteration failed: %v", err)
+	}
+
+	if iteration != 1 {
+		t.Fatalf("expected runLLMIteration to stop after 1 iteration, got %d", iteration)
+	}
+	if provider.callCount != 1 {
+		t.Fatalf("expected provider to be called once, got %d", provider.callCount)
+	}
+}
+
 // failFirstMockProvider fails on the first N calls with a specific error
 type failFirstMockProvider struct {
 	failures    int