kustomize localize generates file names that Windows cannot create

/kind bug

Found while working on #4001.

What happened?

kustomize localize turns parts of remote URLs into local file and directory names. Some of these names are not valid on Windows:

• An IPv6 host becomes a directory name with colons. For example, https://[2001:4860:4860::8888]/file.yaml is localized under 2001:4860:4860::8888/, and Windows does not allow : in file names.
• A URL path segment * becomes a file named *. For example, https://host/* is localized to .../host/*.
• A URL path segment ... becomes a directory named .... Windows drops trailing dots from names, so this directory cannot be created.

What did you expect to happen?

Either localize uses names that are valid on every platform (for example, by escaping the characters that Windows rejects), or it fails early with a clear error that names the URL it cannot localize.

How can we reproduce it (as minimally and precisely as possible)?

Run the localizer unit tests on Windows:

cd api
go test ./internal/localizer/ -run 'TestLocFilePathColon|TestLocFilePath_SpecialChar|TestLocFilePath_SpecialFiles|TestLocRootPath_URLComponents'

These tests check that the names returned by locFilePath and locRootPath can be created on disk.

Expected output

The tests pass, as they do on Linux and macOS.

Actual output

On a GitHub Actions windows-latest runner:

--- FAIL: TestLocFilePathColon
    mkdir ...\TestLocFilePathColon...\001\2001:4860:4860::8888: The filename, directory name, or volume label syntax is incorrect.
--- FAIL: TestLocFilePath_SpecialChar
    open ...\TestLocFilePath_SpecialChar...\001\*: The filename, directory name, or volume label syntax is incorrect.
--- FAIL: TestLocFilePath_SpecialFiles/hidden_files
    mkdir ...\TestLocFilePath_SpecialFileshidden_files...\001\...: Cannot create a file when that file already exists.
--- FAIL: TestLocRootPath_URLComponents/IPv6
    mkdir ...\localized-files\2001:4860:4860::8888: The filename, directory name, or volume label syntax is incorrect.

I have not run kustomize localize itself on Windows against URLs like these. These failures come from the unit tests.

Kustomize version

Built from master at 078ab6cf8.

Operating system

Windows (GitHub Actions windows-latest)

Claude Code on behalf of Adriano Machado (@ammachado)

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