[BUG] In Claude Desktop's third-party inference mode, files other than `SKILL.md` are ignored when importing Agent Skills

### Preflight Checklist

- [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) and this hasn't been reported yet
- [x] This is a single bug report (please file separate reports for different bugs)
- [x] I am using the latest version of Claude Code

### What's Wrong?

In third-party inference mode (such as AWS Bedrock) of Claude Desktop, when importing an Agent Skill that contains files other than `SKILL.md` (such as `references/*.md`) via "Settings" -> "Skills" -> "Add" -> "Upload a skill", all files other than `SKILL.md` are ignored.

### What Should Happen?

Files other than SKILL.md, such as `references/*` and `assets/*`, are also imported.

### Error Messages/Logs

```shell
No error messages or logs.
```

### Steps to Reproduce

1. Create a zip archive containing `SKILL.md` and `references/*.md`
2. Configure third-party inference in Claude Desktop
3. Import the zip archive via "Settings" -> "Skills" -> "Add" -> "Upload a skill"
4. Only `SKILL.md` is copied to the skill directory

### Claude Model

None

### Is this a regression?

I don't know

### Last Working Version

_No response_

### Claude Code Version

1.32885.1

### Platform

AWS Bedrock

### Operating System

macOS

### Terminal/Shell

Terminal.app (macOS)

### Additional Information

This issue reproduces in the same way on both Windows and macOS.

The issue names no repository files or tests. First reproduce the upload flow in Claude Desktop with third-party inference enabled and an archive containing SKILL.md, references, and assets; trace where the skill archive is unpacked. Done means files beyond SKILL.md are preserved in the skill directory on both macOS and Windows.

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