fix: defer sandbox cleanup until stream completes

[sweetmantech]

Summary

• Root cause: The finally block in /api/agent/route.ts called sandbox.stop() immediately when createAgentUIStreamResponse returned the Response object — before the client started consuming the stream. This destroyed the Vercel Sandbox before the agent could execute any bash tool calls, causing every command to fail with [Tool Error] Tool execution error.
• Fix: Replaced the finally block with a TransformStream wrapper that pipes the response body through and calls sandbox.stop() in the .finally() callback of pipeTo(), ensuring cleanup happens only after the stream completes (or errors/disconnects).
• Not an ENV error: The issue was a sandbox lifecycle bug, not a missing environment variable.

Test plan

• Run agent "What is just-bash?" and verify bash commands execute successfully
• Verify multi-turn agent conversations work (agent "list the files" then agent "show me the README")
• Verify sandbox cleanup still happens after stream ends (no sandbox leaks)
• Verify error handling: if sandbox creation fails, the error propagates correctly

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated (UTC)
just-bash	Ready	Preview	Feb 9, 2026 2:25pm

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch sweetmantech/myc-4186-bash-agent-commands-failing-is-this-an-env-error

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