prefixfs

Makes an underlying filesystem accessible only under a prefix path. The inverse of fs.Sub.

Design

• New(fsys, prefix) panics if the cleaned prefix is not a valid, non-root fs.ValidPath
• Opening "." or any ancestor of the prefix returns a synthetic dir that lists only the next path component
• Opening exactly the prefix returns the underlying FS root (".")
• Opening a path under the prefix strips the prefix and delegates to the underlying FS

Key Types

• dir: synthetic read-only directory returned for paths above the prefix boundary
• dirEntry / dirInfo: minimal fs.DirEntry / fs.FileInfo for synthetic directories

Relationships

• Pure io/fs package — does not depend on ihfs types; usable with any fs.FS

Coverage

Aim for high coverage, but do not write messy or low-value tests just to hit 100%. If a branch requires complex setup with little benefit, skip it.