VM Freeze on `capsem-pty-agent` Exit

[tholop]

During an Antigravity conversation inside a Capsem VM, agy executed /run/capsem-pty-agent --help. This resulted in the machine freezing, and the only way out was to go back to the dashboard to pause and restart the VM.

I could reproduce the bug manually like this:

• Create a new VM and log into the terminal
• Open tmux, check that the first pane is active (e.g. run pwd)
• Go to the second tmux pane, and type /run/capsem-pty-agent --help.
• The VM immediately hangs.

I attached an AI-generated bug report below. If this is not working as intended, I'm happy to work on a PR, at least for the basic fixes to capsem-pty-agent such as adding argument parsing and locks.

bug-report-pty-agent-freeze.md