What
The sandbox is the restricted area Claude Code can run commands in, so they cannot touch files outside the places they are allowed to. On Linux, when a write goes through a symlink (a file that points to another file or folder), the sandbox now follows the chain of links to see where the write would actually end up.
If it cannot work that out, it shows a warning saying where the write would land cannot be settled, and it blocks the link instead of allowing it.
Files opened inside the sandbox can now also be written to. A write with a negative or fractional offset, length or position is refused with an error.
Why
This makes the Linux sandbox handle folder layouts that use symlinks, both when the sandbox starts up and when files are written.