In the latest Bamboo versions (5.x) we added the AgentHome/xml-data/build-dir/logs directory to store the build logs on the remote agent, but it seems like there are some issues:

1) For Windows remote agents the log files show as 0KB for size, and when one tries to open the logs files in a text editor, there is a process holding the file (some editors show the content and start adding time stamp text, others fail to open the files). For Mac agents, the files are empty.
2) When running a build expiry, Bamboo doesn't delete the log files from here (from the remote agent).