After writing a file, Claude Code now stat()s the result and compares the on-disk size against the expected byte count. If they differ, it throws immediately rather than silently leaving a truncated file.
This catches a class of failure that commonly occurs on network drives, NFS mounts, and cloud-sync folders (Dropbox, OneDrive, etc.) where the OS kernel reports write success even though the backing store silently truncated the data.
Error text: "Write verification failed: <path> is <N> bytes on disk, expected <M>. The filesystem may have silently truncated the write (network drive / cloud sync)."
Post-write check (search for "writeTextContent: on-disk size mismatch after write") — YSe() at line ~55365
Strings lifted out of the shipped bundle, so the claim above can be checked against them.