diff --git a/core/schemas/responses.go b/core/schemas/responses.go
index 50b4c1cdd7..b572890cc4 100644
--- a/core/schemas/responses.go
+++ b/core/schemas/responses.go
@@ -1,6 +1,7 @@
 package schemas
 
 import (
+	"encoding/json"
 	"fmt"
 	"reflect"
 	"strings"
@@ -928,6 +929,11 @@ type ResponsesMessage struct {
 	Role    *ResponsesMessageRoleType `json:"role,omitempty"`
 	Content *ResponsesMessageContent  `json:"content,omitempty"`
 
+	// Author and Recipient are required on multi-agent collab_tool_call items.
+	// Preserved as raw JSON to survive bifrost round-trip without schema coupling.
+	Author    json.RawMessage `json:"author,omitempty"`
+	Recipient json.RawMessage `json:"recipient,omitempty"`
+
 	*ResponsesToolMessage // For Tool calls and outputs
 
 	CacheControl *CacheControl `json:"cache_control,omitempty"` // Carries cache_control for function_call and function_call_output message types
@@ -1018,6 +1024,9 @@ type ResponsesMessageContentBlock struct {
 	FileID    *string                          `json:"file_id,omitempty"` // Reference to uploaded file
 	Text      *string                          `json:"text,omitempty"`
 	Signature *string                          `json:"signature,omitempty"` // Signature of the content (for reasoning)
+	// EncryptedContent is required on reasoning content blocks during history replay.
+	// OpenAI returns it alongside summary_text blocks; it must be echoed back verbatim.
+	EncryptedContent *string `json:"encrypted_content,omitempty"`
 
 	*ResponsesInputMessageContentBlockImage
 	*ResponsesInputMessageContentBlockFile