Fix wording, docs and style inconsistencies per audit of 0139564

internal/agents/codex.go

@@ -3,6 +3,7 @@ package agents
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"log/slog"
 	"os"
@@ -239,7 +240,7 @@ func codexToolResult(item codex.ThreadItem) (any, bool, error) {
 			}
 			mime, data, ok := strings.Cut(strings.TrimPrefix(c.ImageURL, "data:"), ";base64,")
 			if !ok {
-				return nil, false, fmt.Errorf("dynamic tool image is not a base64 data url")
+				return nil, false, errors.New("dynamic tool image is not a base64 data url")
 			}
 			blocks = append(blocks, imageBlock(mime, data))
 		}