fix(adk): dedupe empty model context snapshots (#1115)

Author: shentongmartin

adk/chatmodel.go

@@ -93,21 +93,48 @@ func copyModelContextEvent(event *ModelContextEvent) *ModelContextEvent {
 		return nil
 	}
 	return &ModelContextEvent{
-		ToolInfos:         append([]*schema.ToolInfo{}, event.ToolInfos...),
-		DeferredToolInfos: append([]*schema.ToolInfo{}, event.DeferredToolInfos...),
+		ToolInfos:         cloneToolInfos(event.ToolInfos),
+		DeferredToolInfos: cloneToolInfos(event.DeferredToolInfos),
 	}
 }
 
+func cloneToolInfos(infos []*schema.ToolInfo) []*schema.ToolInfo {
+	if infos == nil {
+		return nil
+	}
+	return append([]*schema.ToolInfo{}, infos...)
+}
+
+func modelContextEventEqual(a, b *ModelContextEvent) bool {
+	if a == nil || b == nil {
+		return a == b
+	}
+	return toolInfosEqual(a.ToolInfos, b.ToolInfos) &&
+		toolInfosEqual(a.DeferredToolInfos, b.DeferredToolInfos)
+}
+
+func toolInfosEqual(a, b []*schema.ToolInfo) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if !reflect.DeepEqual(a[i], b[i]) {
+			return false
+		}
+	}
+	return true
+}
+
 func syncModelContextSessionEvent[M MessageType](ctx context.Context, state *TypedChatModelAgentState[M]) {
 	execCtx := getTypedChatModelAgentExecCtx[M](ctx)
 	if execCtx == nil || !execCtx.sessionEvents || state == nil {
 		return
 	}
 	current := &ModelContextEvent{
-		ToolInfos:         append([]*schema.ToolInfo{}, state.ToolInfos...),
-		DeferredToolInfos: append([]*schema.ToolInfo{}, state.DeferredToolInfos...),
+		ToolInfos:         cloneToolInfos(state.ToolInfos),
+		DeferredToolInfos: cloneToolInfos(state.DeferredToolInfos),
 	}
-	changed := !execCtx.sawModelContext || !reflect.DeepEqual(execCtx.lastModelContext, current)
+	changed := !execCtx.sawModelContext || !modelContextEventEqual(execCtx.lastModelContext, current)
 	if changed {
 		execCtx.send(ctx, &TypedAgentEvent[M]{
 			SessionEventVariant: &SessionEventVariant[M]{

adk/session.go

@@ -1667,8 +1667,8 @@ func replayDurableContextEvents[M MessageType](events []*SessionEvent[M]) (*reco
 			return nil, fmt.Errorf("reconstruct: %w", err)
 		}
 		if events[i] != nil && events[i].ModelContext != nil {
-			state.ToolInfos = append([]*schema.ToolInfo{}, events[i].ModelContext.ToolInfos...)
-			state.DeferredToolInfos = append([]*schema.ToolInfo{}, events[i].ModelContext.DeferredToolInfos...)
+			state.ToolInfos = cloneToolInfos(events[i].ModelContext.ToolInfos)
+			state.DeferredToolInfos = cloneToolInfos(events[i].ModelContext.DeferredToolInfos)
 			state.sawModelContext = true
 		}
 	}

adk/session_test.go

@@ -610,6 +610,37 @@ func TestRunnerSessionModePrependsCommittedMessagesOnce(t *testing.T) {
 	assert.Equal(t, "value", secondAgent.values[0]["override"])
 }
 
+func TestRunnerSessionModeSkipsDuplicateEmptyModelContext(t *testing.T) {
+	ctx := context.Background()
+	store := newSessionHelperStore()
+	sessionID := "runner-model-context-session"
+	model := &leadingSystemTestModel[*schema.Message]{response: schema.AssistantMessage("ok", nil)}
+	agent, err := NewChatModelAgent(ctx, &ChatModelAgentConfig{
+		Name:        "runner-model-context-agent",
+		Description: "runner model context agent",
+		Instruction: "You are a helpful assistant.",
+		Model:       model,
+	})
+	require.NoError(t, err)
+
+	runner := NewRunner(ctx, RunnerConfig{
+		Agent:        agent,
+		SessionID:    sessionID,
+		SessionStore: store,
+	})
+	drainSessionEvents(t, runner.Query(ctx, "first"))
+	drainSessionEvents(t, runner.Query(ctx, "second"))
+
+	result, err := store.LoadEventsForSession(ctx, sessionID, &LoadSessionEventsRequest{
+		Kinds: []SessionEventKind{SessionEventModelContext},
+	})
+	require.NoError(t, err)
+	require.Len(t, result.Events, 1)
+	require.NotNil(t, result.Events[0].ModelContext)
+	assert.Empty(t, result.Events[0].ModelContext.ToolInfos)
+	assert.Empty(t, result.Events[0].ModelContext.DeferredToolInfos)
+}
+
 func TestAttack_SessionEventIDGeneratorCoversRunnerEvents(t *testing.T) {
 	ctx := context.Background()
 	store := newSessionHelperStore()