fix: increase scanner buffer limit and track stream errors in tape (babysit)

- scanMaxID: increase bufio.Scanner buffer to 10MB to handle large
  tool outputs that exceed the default 64KB token limit
- OnEndWithStreamOutput: track stream read errors and emit run event
  with "error" status instead of always reporting "ok"

Author: STRRL

pkg/tape/eino_handler.go

@@ -230,13 +230,15 @@ func (h *EinoHandler) OnEndWithStreamOutput(ctx context.Context, info *callbacks
 			output.Close()
 		}()
 		var chunks []callbacks.CallbackOutput
+		var streamErr error
 		for {
 			ch, err := output.Recv()
 			if errors.Is(err, io.EOF) {
 				break
 			}
 			if err != nil {
 				log.Printf("tape stream output recv: %v", err)
+				streamErr = err
 				break
 			}
 			chunks = append(chunks, ch)
@@ -250,7 +252,11 @@ func (h *EinoHandler) OnEndWithStreamOutput(ctx context.Context, info *callbacks
 		if msg != nil {
 			h.write(Message(messageToMap(msg), h.baseMeta()))
 		}
-		runData := map[string]any{"status": "ok"}
+		status := "ok"
+		if streamErr != nil {
+			status = "error"
+		}
+		runData := map[string]any{"status": status}
 		if usage != nil {
 			runData["usage"] = map[string]any{
 				"prompt_tokens":     usage.PromptTokens,

pkg/tape/jsonl.go

@@ -44,6 +44,8 @@ func scanMaxID(path string) (int64, error) {
 
 	var maxID int64
 	sc := bufio.NewScanner(f)
+	// Allow entries up to 10 MB to handle large tool outputs in tape lines.
+	sc.Buffer(make([]byte, 0, 64*1024), 10*1024*1024)
 	for sc.Scan() {
 		var row struct {
 			ID int64 `json:"id"`