[BUG] Agent editor incorrectly resolves file paths when editing agents

Description:
When attempting to edit an agent's MCP server access through the Claude UI (/agents → select agent → Edit
agent → Edit tools → Advanced options), the system fails to locate the agent definition file.

Steps to Reproduce:

1. Create an agent in ~/.claude/agents/haskell-refactoring.md
2. Start Claude in any directory (e.g., /home/user/Documents/DemoProj/)
3. Run /agents command
4. Select the agent and choose "Edit agent"
5. Select "Edit tools" then "Advanced options"
6. Attempt to modify MCP server access

Expected Behavior:
Claude should locate and edit the agent file at ~/.claude/agents/haskell-refactoring.md

Actual Behavior:
Claude throws an error looking for the file at an incorrect doubled path:

• When in project directory: ENOENT: no such file or directory, open

'/home/user/Documents/DemoProj/.claude/agents/haskell-refactoring.md'

• When attempting to edit from home: ENOENT: no such file or directory, open

'/home/user/.claude/agents/.claude/agents/haskell-refactoring.md'

Environment:

• Platform: Linux
• OS Version: Linux 6.1.0-38-arm64

Workaround:
Manually edit the agent file directly instead of using the Claude UI.

Impact:
Users cannot modify agent configurations through the intended UI workflow, forcing them to manually edit
configuration files.