fix(openai): handle transcript replacement after websocket compaction

- Add shouldReplaceWebsocketTranscript() to detect historical model output in input
- Add normalizeResponseTranscriptReplacement() for full transcript reset handling
- Prevent duplicate stale turn-state when clients replace local history post-compaction
- Avoid orphaned function_call items from incremental append on compact transcripts
- Add unit tests for transcript replacement detection and state reset behavior

sdk/api/handlers/openai/openai_responses_websocket.go

@@ -277,6 +277,15 @@ func normalizeResponseSubsequentRequest(rawJSON []byte, lastRequest []byte, last
 		}
 	}
 
+	// Compaction can cause clients to replace local websocket history with a new
+	// compact transcript on the next `response.create`. When the input already
+	// contains historical model output items, treating it as an incremental append
+	// duplicates stale turn-state and can leave late orphaned function_call items.
+	if shouldReplaceWebsocketTranscript(rawJSON, nextInput) {
+		normalized := normalizeResponseTranscriptReplacement(rawJSON, lastRequest)
+		return normalized, bytes.Clone(normalized), nil
+	}
+
 	// Websocket v2 mode uses response.create with previous_response_id + incremental input.
 	// Do not expand it into a full input transcript; upstream expects the incremental payload.
 	if allowIncrementalInputWithPreviousResponseID {
@@ -348,6 +357,54 @@ func normalizeResponseSubsequentRequest(rawJSON []byte, lastRequest []byte, last
 	return normalized, bytes.Clone(normalized), nil
 }
 
+func shouldReplaceWebsocketTranscript(rawJSON []byte, nextInput gjson.Result) bool {
+	if strings.TrimSpace(gjson.GetBytes(rawJSON, "type").String()) != wsRequestTypeCreate {
+		return false
+	}
+	if strings.TrimSpace(gjson.GetBytes(rawJSON, "previous_response_id").String()) != "" {
+		return false
+	}
+	if !nextInput.Exists() || !nextInput.IsArray() {
+		return false
+	}
+
+	for _, item := range nextInput.Array() {
+		switch strings.TrimSpace(item.Get("type").String()) {
+		case "function_call":
+			return true
+		case "message":
+			role := strings.TrimSpace(item.Get("role").String())
+			if role == "assistant" || role == "developer" {
+				return true
+			}
+		}
+	}
+
+	return false
+}
+
+func normalizeResponseTranscriptReplacement(rawJSON []byte, lastRequest []byte) []byte {
+	normalized, errDelete := sjson.DeleteBytes(rawJSON, "type")
+	if errDelete != nil {
+		normalized = bytes.Clone(rawJSON)
+	}
+	normalized, _ = sjson.DeleteBytes(normalized, "previous_response_id")
+	if !gjson.GetBytes(normalized, "model").Exists() {
+		modelName := strings.TrimSpace(gjson.GetBytes(lastRequest, "model").String())
+		if modelName != "" {
+			normalized, _ = sjson.SetBytes(normalized, "model", modelName)
+		}
+	}
+	if !gjson.GetBytes(normalized, "instructions").Exists() {
+		instructions := gjson.GetBytes(lastRequest, "instructions")
+		if instructions.Exists() {
+			normalized, _ = sjson.SetRawBytes(normalized, "instructions", []byte(instructions.Raw))
+		}
+	}
+	normalized, _ = sjson.SetBytes(normalized, "stream", true)
+	return bytes.Clone(normalized)
+}
+
 func websocketUpstreamSupportsIncrementalInput(attributes map[string]string, metadata map[string]any) bool {
 	if len(attributes) > 0 {
 		if raw := strings.TrimSpace(attributes["websockets"]); raw != "" {