[BUG] `/export` does not resolve absolute paths or expand tilde in filename argument

Preflight Checklist

• [x] I have searched existing issues 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?

The /export command treats absolute paths and ~ as literal strings, prepending the current working directory instead of resolving them. This makes it impossible to export to a specific directory using an absolute path.

What Should Happen?

1. Paths starting with / should be used as absolute paths.
2. ~ should expand to the user's home directory.

Error Messages/Logs

> /export /Users/rps/Desktop/test
  Failed to export conversation: ENOENT: no such file or directory, open '/Users/rps/Desktop/old-github/claude-code/Users/rps/Desktop/test.txt'                                                                    
                                                                                                                                                                                                                     
> /export ~/Desktop/test                                                                                                                                                                                           
  Failed to export conversation: ENOENT: no such file or directory, open '/Users/rps/Desktop/old-github/claude-code/~/Desktop/test.txt'

Steps to Reproduce

1. Open Claude Code in any project directory
2. Run /export /Users/<you>/Desktop/test
3. Observe the error shows cwd prepended to the absolute path
4. Run /export ~/Desktop/test
5. Observe ~ is treated as a literal character in the path

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.92 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

The /export command appears to support relative paths with extensions (e.g., /export ../../test.txt correctly resolves the path), but this is undocumented. /help export provides no information about supported arguments, path syntax, or expected behavior.

The presence or absence of a file extension in the first argument fundamentally changes how the command parses input:

• With extension: only first arg used as filename, relative paths resolve, destination arg silently ignored
• Without extension: all args concatenated as filename, relative paths mangled

This suggests the path resolution logic exists but is gated behind extension detection, and the no-extension code path has a different (broken) implementation.

Tested on macOS with both Opus 4.5 and Opus 4.6 — identical behavior.