[sep2]

Fixes #23986.

Use path.win32.normalize() for paths beginning with //, then convert the result to forward slashes. This preserves Windows device and UNC roots, including node:vfs mount points. Other paths keep the existing POSIX normalization.

Regression tests cover device/UNC paths, relative segments, trailing separators, idempotence, native Windows separators, POSIX filenames, and reading a mounted node:vfs file through its normalized path.

Validation

• pnpm build
• pnpm --filter vite typecheck
• Full unit suite on macOS with Node 24.19.0, 26.5.0, and 26.13.0
• Windows Node 26.13.0 verification: the upstream implementation reproduces the VFS ENOENT; the fixed implementation passes all 1,124 unit tests
• Oxfmt and Oxlint checks on both changed files

AI assistance

A coding agent prepared the implementation and tests and ran the checks above. The approach delegates namespace handling to Node rather than reconstructing path prefixes manually; the before/after Windows run verifies that normalized paths still address the same mounted memory files.