[FEATURE] Support @ references for files in /add-dir directories

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

I often need to reference code from other local repositories, but Claude Code doesn't support using @ to reference files in directories added via /add-dir.
The current workflow requires me to manually type full absolute paths or read files first before I can reference them, which is tedious and error-prone.

Proposed Solution

I would like to be able to reference files from added directories using a prefix syntax like @workspace:alias/<filepath>, while keeping @ for the current workspace. For example:

/add-dir /path/to/other-project as other
@workspace:other/src/utils.ts // reference from other project
@src/utils.ts // reference from current project

This prefix approach avoids conflicts with files in the current directory and clearly indicates the file is from another workspace.

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

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Additional Context

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