[BUG] Managed Agents bash tool crashes with tmux timeout in cloud container

Description

When creating a Managed Agents session with agent_toolset_20260401 (built-in bash tool) and networking: { type: 'unrestricted' }, every bash command crashes or times out with tmux/temp-file errors. The execution environment is non-functional.

Reproduction

1. Create an agent with agent_toolset_20260401
2. Create a cloud environment with networking: { type: 'unrestricted' }
3. Start a session and send a message that triggers bash usage
4. Observe: bash commands crash with tmux command timed out after 295s and /bin/sh: cannot open /tmp/ale-XXXXXX.out: No such file

Session Details

• Session ID: sesn_011Ca3nSaVc4aW6Xkouzh96c
• Created: 2026-04-14T14:00:12Z
• Status: idle (ended after 4 hours of retrying)
• 285 events, mostly failed bash attempts

Error Output

tmux command timed out after 295s
/bin/sh: 12: cannot open /tmp/ale-XXXXXX.out: No such file

Every bash command — including basic pwd — fails with this error. The agent correctly diagnosed it as a system-level issue.

Context

This session was created programmatically from a CCR scheduled trigger via launch-remote.ts. The goal is to run a daily newsletter pipeline that needs outbound HTTP access to external services (Supabase, PubMed, Brave Search, ReSend). The CCR sandbox egress proxy blocks these services, so we need the CMA environment's unrestricted networking.

Expected Behavior

Bash commands should execute normally in the managed agent container with unrestricted networking.

Environment

• SDK: @anthropic-ai/sdk ^0.87.0
• Beta header: managed-agents-2026-04-01
• Model: claude-sonnet-4-6
• OS: Created from CCR trigger (macOS client)