Stop execute agents from decoding files in the sandbox

[baggiiiie]

hey @RhysSullivan , i attempted a fix on the first half of issue #1509 regarding the base64 issue. please have a look and let me know if this fix is desirable :D

fix

The execute skill told agents to decode ToolFile.data and base64 content fields with runtime globals unavailable in QuickJS. Agents attempted atob and Buffer before falling back to the ToolFile path.

• Tell agents to wrap base64 JSON byte fields in a ToolFile and emit them.
• Explicitly prohibit decoding or transcoding with unavailable globals.
• Clarify that Gmail attachments are already ToolFiles: emit them to display them, or pass their data through bodyBase64 to forward them.

Closes #1509

verification

below is a fix verification with the same prompt from original issue:

use `executor` to fetch a text file from any GitHub repo you have access to via `repos.getContent`, show content

stop and report if there's any error during the executor call and show me the code u wrote

same prompt verification	skill read by agent