feat(sse): implement CodexSSEScanner for improved event data handling

Closes: #6575

internal/runtime/executor/codex_executor_execute.go

@@ -137,11 +137,12 @@ func (e *CodexExecutor) Execute(ctx context.Context, auth *cliproxyauth.Auth, re
 	data, errRead := io.ReadAll(httpResp.Body)
 	helps.AppendAPIResponseChunk(ctx, e.cfg, data)
 
-	lines := bytes.Split(data, []byte("\n"))
+	events := helps.NewCodexSSEScanner(ctx, bytes.NewReader(data), len(data)+1)
 	outputItemsByIndex := make(map[int64][]byte)
 	var outputItemsFallback [][]byte
 	sawOutputDelta := false
-	for _, line := range lines {
+	for events.Scan() {
+		line := events.Bytes()
 		if !bytes.HasPrefix(line, dataTag) {
 			continue
 		}