feat(adk): add summarization middleware (#729)

Author: mrh997

adk/middlewares/summarization/consts.go

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2026 CloudWeGo Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package summarization
+
+const (
+	extraKeyContentType = "_eino_summarization_content_type"
+)
+
+type summarizationContentType string
+
+const (
+	contentTypeSummary summarizationContentType = "summary"
+)
+
+type ActionType string
+
+const (
+	ActionTypeBeforeSummary ActionType = "before_summary"
+	ActionTypeAfterSummary  ActionType = "after_summary"
+)

adk/middlewares/summarization/customized_action.go

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2026 CloudWeGo Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package summarization
+
+import (
+	"github.com/cloudwego/eino/adk"
+)
+
+type CustomizedAction struct {
+	// Type is the action type.
+	Type ActionType `json:"type"`
+
+	// Before is set when Type is ActionTypeBeforeSummary.
+	// Emitted after trigger condition is met, before calling model to generate summary.
+	Before *BeforeSummaryAction `json:"before,omitempty"`
+
+	// After is set when Type is ActionTypeAfterSummary.
+	// Emitted after summary generation, before applying new messages to state.
+	After *AfterSummaryAction `json:"after,omitempty"`
+}
+
+type BeforeSummaryAction struct {
+	// Messages is the original state messages before summarization.
+	Messages []adk.Message `json:"messages,omitempty"`
+}
+
+type AfterSummaryAction struct {
+	// Messages is the final state messages after summarization.
+	Messages []adk.Message `json:"messages,omitempty"`
+}