From 82d574eb7b85c16d97a1697b3224505d72a7c49d Mon Sep 17 00:00:00 2001
From: Alix-007 <267018309+Alix-007@users.noreply.github.com>
Date: Fri, 20 Mar 2026 14:37:47 +0800
Subject: [PATCH] fix(agent): separate empty-response and tool-limit fallbacks

---
 pkg/agent/loop.go      |   9 ++-
 pkg/agent/loop_test.go | 129 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 136 insertions(+), 2 deletions(-)

diff --git a/pkg/agent/loop.go b/pkg/agent/loop.go
index ef2b9e28f..637cd506c 100644
--- a/pkg/agent/loop.go
+++ b/pkg/agent/loop.go
@@ -70,7 +70,8 @@ type processOptions struct {
 }
 
 const (
-	defaultResponse           = "I've completed processing but have no response to give. Increase `max_tool_iterations` in config.json."
+	defaultResponse           = "The model returned an empty response. This may indicate a provider error or token limit."
+	toolLimitResponse         = "I've reached `max_tool_iterations` without a final response. Increase `max_tool_iterations` in config.json if this task needs more tool steps."
 	sessionKeyAgentPrefix     = "agent:"
 	metadataKeyAccountID      = "account_id"
 	metadataKeyGuildID        = "guild_id"
@@ -935,7 +936,11 @@ func (al *AgentLoop) runAgentLoop(
 
 	// 4. Handle empty response
 	if finalContent == "" {
-		finalContent = opts.DefaultResponse
+		if iteration >= agent.MaxIterations && agent.MaxIterations > 0 {
+			finalContent = toolLimitResponse
+		} else {
+			finalContent = opts.DefaultResponse
+		}
 	}
 
 	// 5. Save final assistant message to session
diff --git a/pkg/agent/loop_test.go b/pkg/agent/loop_test.go
index b6b6c2c6c..28eab03db 100644
--- a/pkg/agent/loop_test.go
+++ b/pkg/agent/loop_test.go
@@ -420,6 +420,29 @@ func (m *countingMockProvider) GetDefaultModel() string {
 	return "counting-mock-model"
 }
 
+type toolLimitOnlyProvider struct{}
+
+func (m *toolLimitOnlyProvider) Chat(
+	ctx context.Context,
+	messages []providers.Message,
+	tools []providers.ToolDefinition,
+	model string,
+	opts map[string]any,
+) (*providers.LLMResponse, error) {
+	return &providers.LLMResponse{
+		ToolCalls: []providers.ToolCall{{
+			ID:        "call_tool_limit_test",
+			Type:      "function",
+			Name:      "tool_limit_test_tool",
+			Arguments: map[string]any{"value": "x"},
+		}},
+	}, nil
+}
+
+func (m *toolLimitOnlyProvider) GetDefaultModel() string {
+	return "tool-limit-only-model"
+}
+
 // mockCustomTool is a simple mock tool for registration testing
 type mockCustomTool struct{}
 
@@ -442,6 +465,29 @@ func (m *mockCustomTool) Execute(ctx context.Context, args map[string]any) *tool
 	return tools.SilentResult("Custom tool executed")
 }
 
+type toolLimitTestTool struct{}
+
+func (m *toolLimitTestTool) Name() string {
+	return "tool_limit_test_tool"
+}
+
+func (m *toolLimitTestTool) Description() string {
+	return "Tool used to exhaust the iteration budget in tests"
+}
+
+func (m *toolLimitTestTool) Parameters() map[string]any {
+	return map[string]any{
+		"type": "object",
+		"properties": map[string]any{
+			"value": map[string]any{"type": "string"},
+		},
+	}
+}
+
+func (m *toolLimitTestTool) Execute(ctx context.Context, args map[string]any) *tools.ToolResult {
+	return tools.SilentResult("tool limit test result")
+}
+
 // testHelper executes a message and returns the response
 type testHelper struct {
 	al *AgentLoop
@@ -1083,6 +1129,89 @@ func TestAgentLoop_ContextExhaustionRetry(t *testing.T) {
 	}
 }
 
+func TestAgentLoop_EmptyModelResponseUsesAccurateFallback(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: 3,
+			},
+		},
+	}
+
+	msgBus := bus.NewMessageBus()
+	provider := &simpleMockProvider{response: ""}
+	al := NewAgentLoop(cfg, msgBus, provider)
+
+	response, err := al.ProcessDirectWithChannel(context.Background(), "hello", "empty-response", "test", "chat1")
+	if err != nil {
+		t.Fatalf("ProcessDirectWithChannel failed: %v", err)
+	}
+	if response != defaultResponse {
+		t.Fatalf("response = %q, want %q", response, defaultResponse)
+	}
+}
+
+func TestAgentLoop_ToolLimitUsesDedicatedFallback(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: 1,
+			},
+		},
+	}
+
+	msgBus := bus.NewMessageBus()
+	provider := &toolLimitOnlyProvider{}
+	al := NewAgentLoop(cfg, msgBus, provider)
+	al.RegisterTool(&toolLimitTestTool{})
+
+	response, err := al.ProcessDirectWithChannel(context.Background(), "hello", "tool-limit", "test", "chat1")
+	if err != nil {
+		t.Fatalf("ProcessDirectWithChannel failed: %v", err)
+	}
+	if response != toolLimitResponse {
+		t.Fatalf("response = %q, want %q", response, toolLimitResponse)
+	}
+
+	defaultAgent := al.registry.GetDefaultAgent()
+	if defaultAgent == nil {
+		t.Fatal("No default agent found")
+	}
+	route := al.registry.ResolveRoute(routing.RouteInput{
+		Channel: "test",
+		Peer: &routing.RoutePeer{
+			Kind: "direct",
+			ID:   "cron",
+		},
+	})
+	history := defaultAgent.Sessions.GetHistory(route.SessionKey)
+	if len(history) != 4 {
+		t.Fatalf("history len = %d, want 4", len(history))
+	}
+	assertRoles(t, history, "user", "assistant", "tool", "assistant")
+	if history[3].Content != toolLimitResponse {
+		t.Fatalf("final assistant content = %q, want %q", history[3].Content, toolLimitResponse)
+	}
+}
+
 // TestProcessDirectWithChannel_TriggersMCPInitialization verifies that
 // ProcessDirectWithChannel triggers MCP initialization when MCP is enabled.
 // Note: Manager is only initialized when at least one MCP server is configured