fix(identity): 避免未配置 SSF 时触发空指针

SecurityEventReceiver 不再把空 ConnectionManager 包装为非空接口；未启用 SSF 时公开端点明确返回 404。补充运行时和 HTTP 回归测试。\n\n验证：go test ./internal/identityruntime ./internal/httpapi。

apps/api/internal/httpapi/security_events_test.go

@@ -40,6 +40,18 @@ func TestReceiveSecurityEventUsesPreparedReceiverBeforeFirstActivation(t *testin
 	}
 }
 
+func TestReceiveSecurityEventReturnsNotFoundWithoutConfiguredReceiver(t *testing.T) {
+	server := &Server{identityRuntime: identityruntime.NewManager(nil, &preparedReceiverBuilder{})}
+	request := httptest.NewRequest(http.MethodPost, "/api/v1/security-events/ssf", nil)
+	response := httptest.NewRecorder()
+
+	server.receiveSecurityEvent(response, request)
+
+	if response.Code != http.StatusNotFound {
+		t.Fatalf("unconfigured SSF status=%d, want %d", response.Code, http.StatusNotFound)
+	}
+}
+
 func TestSecurityEventWriteAuditFailsClosedBeforeMutation(t *testing.T) {
 	server := &Server{}
 	request := httptest.NewRequest(http.MethodPost, "/api/admin/system/security-events/connection/verify", nil)

apps/api/internal/identityruntime/manager.go

@@ -105,7 +105,10 @@ func (manager *Manager) SecurityEventReceiver() http.Handler {
 	if runtime := manager.Current(); runtime != nil && runtime.SecurityEvents != nil {
 		return runtime.SecurityEvents
 	}
-	return manager.SecurityEventManager()
+	if securityEventManager := manager.SecurityEventManager(); securityEventManager != nil {
+		return securityEventManager
+	}
+	return nil
 }
 
 // SecurityEventManager resolves the manager used by administrative recovery

apps/api/internal/identityruntime/manager_test.go

@@ -630,6 +630,14 @@ func TestSecurityEventManagerExposesPreparedRecoveryManagerWithoutActiveRuntime(
 	}
 }
 
+func TestSecurityEventReceiverReturnsNilWithoutConfiguredManager(t *testing.T) {
+	manager := NewManager(&runtimeRepositoryFake{}, &runtimeBuilderFake{})
+
+	if manager.SecurityEventReceiver() != nil {
+		t.Fatal("unconfigured security event receiver should be nil")
+	}
+}
+
 func TestSecurityEventManagerPrefersActiveRuntime(t *testing.T) {
 	active := &securityevents.ConnectionManager{}
 	prepared := &securityevents.ConnectionManager{}