[BUG] Desktop file viewer blocks files in permissions.additionalDirectories ("This file is outside the working directory") — regression

Summary

In the Claude desktop app, clicking a file that lives inside one of the
permissions.additionalDirectories paths opens the in-app file tab with:

This file is outside the working directory: It can't be opened here, but it may still exist on disk. {path}

The agent itself can read and edit these files without issue (the
additionalDirectories permission works for tools). Only the in-app file
viewer/sidepane refuses to render them, even though the directory is an
explicitly-granted additional working directory.

This is a regression — opening these files in the viewer worked until
~last week.

Environment

• Claude desktop app: 1.15962.1
• Claude Code: 2.1.158
• macOS: 26.5.1 (build 25F80), Apple Silicon
• permissions.additionalDirectories set in project .claude/settings.json,

e.g.:
``json
{
"permissions": {
"additionalDirectories": ["..", "../sibling-repo-a", "../sibling-repo-b"]
}
}
``

Repro

1. In a project, add a sibling directory to

permissions.additionalDirectories (or launch with --add-dir).

1. Ask the agent to read a file in that additional directory — it succeeds.
2. Click that file (e.g. from a clickable file_path reference, or via the

file tab) to open it in the in-app viewer.

1. Expected: the viewer renders the file, since the directory is a granted

additional working directory the agent can already access.

1. Actual: the viewer shows *"This file is outside the working directory:

It can't be opened here, but it may still exist on disk. {path}"*

Impact

The viewer's access scope is narrower than the agent's. A user can't open /
review the very files the agent is editing in an additional directory, which
breaks the multi-repo workspace workflow (reviewing cross-repo changes in the
app). This worked previously, so it reads as an unintended regression in the
viewer's path-scoping check.

Related (not duplicates)

• #50798 — desktop sidepane blocks plan files in ~/.claude/plans/ ("outside

session folder"). Same viewer-scoping component, different path.

• #57153 / #64300 — about Read/Edit permissions on additionalDirectories,

not the file viewer.