Fix: cross execution environment file transfer

[declanjackson]

Fix: Skills directory not transferring to sub-agents

Problem

When a supervisor agent with a skills_dir delegated tasks to sub-agents, the skills directory was not being
transferred to the sub-agent's execution environment for cross-environment transfers.

Root Cause

The upload_files method in CodeExecToolProvider only supported single file transfers for cross-environment
operations (e.g., E2B sandbox to E2B sandbox). When the agent tried to transfer the skills directory:

await state.exec_env.upload_files("skills", source_env=parent_state.exec_env)

The code would call read_file_bytes("skills") which fails because you can't read a directory as bytes. The
transfer silently failed, leaving sub-agents without access to skills.

Additionally, files were being placed in the wrong location (data_analysis/SKILL.md instead of skills/data_analysis/SKILL.md) because the source directory name wasn't being preserved.

Solution

Added two new abstract methods to CodeExecToolProvider:

• is_directory(path) - Check if a path is a directory in the execution environment
• list_files(path) - Recursively list all files in a directory

Updated upload_files to handle directories in cross-environment transfers:

1. Check if the source path is a directory
2. If so, list all files recursively and transfer each one
3. Preserve the source directory name when dest_dir is not specified

Other

This PR also updates the tasks in the following examples:

• examples/browser_use_example.py
• examples/open_responses_example.py