Renaming or moving a path inside the jail

When to use

• Renaming in place inside the same parent directory.
• Moving across directories within the jail.
• Atomic publish of a generated file from a temp name to its final location.

Notes

• Both src and dst are absolute and must be inside the same jail.
• Implementation is rename(2) with a fallback to copy + unlink when src and dst cross filesystems. The fallback is not atomic on its own; a crash after the copy and before the unlink leaves both copies on disk.
• Without overwrite: true the call refuses if dst exists and returns the trigger Err.
• This is mv for one path. There is no batch or glob form; loop in the caller.
• Same jail and denylist rules as shell::fs::ls for both src and dst.