diff --git a/pkg/agent/loop.go b/pkg/agent/loop.go
index 5c257539b..d62b9268f 100644
--- a/pkg/agent/loop.go
+++ b/pkg/agent/loop.go
@@ -264,11 +264,18 @@ func (al *AgentLoop) SetHooks(h *hooks.HookRegistry) error {
 // SetPluginManager installs a plugin manager and routes its hook registry into the loop.
 // Must be called before Run starts.
 func (al *AgentLoop) SetPluginManager(pm *plugin.Manager) error {
-	al.pluginManager = pm
 	if pm == nil {
-		return al.SetHooks(nil)
+		if err := al.SetHooks(nil); err != nil {
+			return err
+		}
+		al.pluginManager = nil
+		return nil
 	}
-	return al.SetHooks(pm.HookRegistry())
+	if err := al.SetHooks(pm.HookRegistry()); err != nil {
+		return err
+	}
+	al.pluginManager = pm
+	return nil
 }
 
 // EnablePlugins is a convenience helper to build and install a plugin manager.
@@ -848,13 +855,17 @@ func (al *AgentLoop) runLLMIteration(
 					toolResult = tools.ErrorResult(reason)
 				}
 				tc.Arguments = btcEvent.Args
+				if tc.Arguments == nil {
+					tc.Arguments = make(map[string]any)
+				}
 			}
 
-			toolStart := time.Now()
+			var toolDuration time.Duration
 			if !toolCanceled {
+				toolStart := time.Now()
 				toolResult = agent.Tools.ExecuteWithContext(ctx, tc.Name, tc.Arguments, opts.Channel, opts.ChatID, asyncCallback)
+				toolDuration = time.Since(toolStart)
 			}
-			toolDuration := time.Since(toolStart)
 
 			// Fire after_tool_call hook (fires for both executed and canceled calls)
 			if al.hooks != nil {
diff --git a/pkg/agent/plugin_test.go b/pkg/agent/plugin_test.go
index d0336956c..115923476 100644
--- a/pkg/agent/plugin_test.go
+++ b/pkg/agent/plugin_test.go
@@ -11,6 +11,8 @@ import (
 	"github.com/sipeed/picoclaw/pkg/config"
 	"github.com/sipeed/picoclaw/pkg/hooks"
 	"github.com/sipeed/picoclaw/pkg/plugin"
+	"github.com/sipeed/picoclaw/pkg/providers"
+	"github.com/sipeed/picoclaw/pkg/tools"
 )
 
 type blockingPlugin struct{}
@@ -32,6 +34,68 @@ func (p blockingPlugin) Register(r *hooks.HookRegistry) error {
 	return nil
 }
 
+type nilArgsProvider struct {
+	calls int
+}
+
+func (p *nilArgsProvider) Chat(
+	_ context.Context,
+	_ []providers.Message,
+	_ []providers.ToolDefinition,
+	_ string,
+	_ map[string]any,
+) (*providers.LLMResponse, error) {
+	if p.calls == 0 {
+		p.calls++
+		return &providers.LLMResponse{
+			Content: "",
+			ToolCalls: []providers.ToolCall{
+				{
+					ID:        "tc-1",
+					Type:      "function",
+					Name:      "nil_args_tool",
+					Arguments: map[string]any{"seed": "value"},
+				},
+			},
+		}, nil
+	}
+	p.calls++
+	return &providers.LLMResponse{
+		Content:   "done",
+		ToolCalls: []providers.ToolCall{},
+	}, nil
+}
+
+func (p *nilArgsProvider) GetDefaultModel() string {
+	return "test-model"
+}
+
+type nilArgsCaptureTool struct {
+	receivedNil bool
+}
+
+func (t *nilArgsCaptureTool) Name() string {
+	return "nil_args_tool"
+}
+
+func (t *nilArgsCaptureTool) Description() string {
+	return "captures whether args are nil"
+}
+
+func (t *nilArgsCaptureTool) Parameters() map[string]any {
+	return map[string]any{
+		"type":       "object",
+		"properties": map[string]any{},
+	}
+}
+
+func (t *nilArgsCaptureTool) Execute(_ context.Context, args map[string]any) *tools.ToolResult {
+	if args == nil {
+		t.receivedNil = true
+	}
+	return tools.SilentResult("ok")
+}
+
 func TestSetPluginManagerInstallsHookRegistry(t *testing.T) {
 	tmpDir, err := os.MkdirTemp("", "agent-plugin-test-*")
 	if err != nil {