diff --git a/core/schemas/utils.go b/core/schemas/utils.go
index 0f9c6f90a0..473b115284 100644
--- a/core/schemas/utils.go
+++ b/core/schemas/utils.go
@@ -1223,11 +1223,26 @@ func DeepCopyResponsesMessage(original ResponsesMessage) ResponsesMessage {
 		copy.Status = &copyStatus
 	}
 
+	if original.Phase != nil {
+		copy.Phase = new(string)
+		*copy.Phase = *original.Phase
+	}
+
 	if original.Role != nil {
 		copyRole := *original.Role
 		copy.Role = &copyRole
 	}
 
+	// Deep copy Author and Recipient (multi-agent collab_tool_call items).
+	// json.RawMessage is a []byte slice; copy the bytes so callers don't share
+	// (and mutate) the underlying array.
+	if original.Author != nil {
+		copy.Author = append(json.RawMessage(nil), original.Author...)
+	}
+	if original.Recipient != nil {
+		copy.Recipient = append(json.RawMessage(nil), original.Recipient...)
+	}
+
 	if original.Content != nil {
 		copy.Content = &ResponsesMessageContent{}
 
@@ -1377,6 +1392,17 @@ func deepCopyResponsesMessageContentBlock(original ResponsesMessageContentBlock)
 		copy.Text = &copyText
 	}
 
+	// Reasoning replay fields: Signature and EncryptedContent are echoed back
+	// verbatim to the provider, so they must survive the deep copy.
+	if original.Signature != nil {
+		copy.Signature = new(string)
+		*copy.Signature = *original.Signature
+	}
+	if original.EncryptedContent != nil {
+		copy.EncryptedContent = new(string)
+		*copy.EncryptedContent = *original.EncryptedContent
+	}
+
 	// Deep copy ResponsesInputMessageContentBlockImage
 	if original.ResponsesInputMessageContentBlockImage != nil {
 		copyImage := &ResponsesInputMessageContentBlockImage{}
diff --git a/framework/streaming/responses.go b/framework/streaming/responses.go
index 63c05c10dd..e6644d6fa6 100644
--- a/framework/streaming/responses.go
+++ b/framework/streaming/responses.go
@@ -1,6 +1,7 @@
 package streaming
 
 import (
+	"encoding/json"
 	"fmt"
 	"sort"
 	"strings"
@@ -219,6 +220,16 @@ func deepCopyResponsesMessage(original schemas.ResponsesMessage) schemas.Respons
 		}
 	}
 
+	// Deep copy Author and Recipient (multi-agent collab_tool_call items).
+	// json.RawMessage is a []byte slice; copy the bytes so accumulators don't
+	// share (and mutate) the underlying array.
+	if original.Author != nil {
+		copy.Author = append(json.RawMessage(nil), original.Author...)
+	}
+	if original.Recipient != nil {
+		copy.Recipient = append(json.RawMessage(nil), original.Recipient...)
+	}
+
 	// Deep copy ResponsesReasoning if present
 	if original.ResponsesReasoning != nil {
 		copy.ResponsesReasoning = &schemas.ResponsesReasoning{}
@@ -443,6 +454,17 @@ func deepCopyResponsesMessageContentBlock(original schemas.ResponsesMessageConte
 		copy.Text = &copyText
 	}
 
+	// Reasoning replay fields: Signature and EncryptedContent are echoed back
+	// verbatim to the provider, so they must survive the deep copy.
+	if original.Signature != nil {
+		copy.Signature = new(string)
+		*copy.Signature = *original.Signature
+	}
+	if original.EncryptedContent != nil {
+		copy.EncryptedContent = new(string)
+		*copy.EncryptedContent = *original.EncryptedContent
+	}
+
 	// Copy other specific content type fields as needed
 	if original.ResponsesOutputMessageContentText != nil {
 		t := *original.ResponsesOutputMessageContentText