Fix: surface workflow container LLM usage (#27021)

api/core/workflow/nodes/base/__init__.py

@@ -1,4 +1,5 @@
 from .entities import BaseIterationNodeData, BaseIterationState, BaseLoopNodeData, BaseLoopState, BaseNodeData
+from .usage_tracking_mixin import LLMUsageTrackingMixin
 
 __all__ = [
     "BaseIterationNodeData",
@@ -6,4 +7,5 @@ __all__ = [
     "BaseLoopNodeData",
     "BaseLoopState",
     "BaseNodeData",
+    "LLMUsageTrackingMixin",
 ]

api/core/workflow/nodes/base/usage_tracking_mixin.py

@@ -0,0 +1,28 @@
+from core.model_runtime.entities.llm_entities import LLMUsage
+from core.workflow.runtime import GraphRuntimeState
+
+
+class LLMUsageTrackingMixin:
+    """Provides shared helpers for merging and recording LLM usage within workflow nodes."""
+
+    graph_runtime_state: GraphRuntimeState
+
+    @staticmethod
+    def _merge_usage(current: LLMUsage, new_usage: LLMUsage | None) -> LLMUsage:
+        """Return a combined usage snapshot, preserving zero-value inputs."""
+        if new_usage is None or new_usage.total_tokens <= 0:
+            return current
+        if current.total_tokens == 0:
+            return new_usage
+        return current.plus(new_usage)
+
+    def _accumulate_usage(self, usage: LLMUsage) -> None:
+        """Push usage into the graph runtime accumulator for downstream reporting."""
+        if usage.total_tokens <= 0:
+            return
+
+        current_usage = self.graph_runtime_state.llm_usage
+        if current_usage.total_tokens == 0:
+            self.graph_runtime_state.llm_usage = usage.model_copy()
+        else:
+            self.graph_runtime_state.llm_usage = current_usage.plus(usage)