Linux: 'Show in File Explorer' displays macOS Security dialog instead of opening file manager #28652

Description

On Linux, clicking "Show in File Explorer" in the Keybase GUI Files section displays a macOS-specific dialog asking to "Open your macOS Security & Privacy Settings" instead of opening the native file manager.

Steps to Reproduce

1. Open Keybase GUI on Linux
2. Navigate to Files section
3. Click "Yes, enable" on the "Enable Keybase in File Explorer?" prompt
4. Or click on "Show in File Explorer" icon next to any folder

Expected Behavior

The native Linux file manager (Nautilus, Dolphin, etc.) should open at the selected KBFS path.

Actual Behavior

A dialog appears with macOS-specific instructions:

• Title: "You need to change your system security preferences."
• Text: "Open your macOS Security & Privacy Settings and follow these steps."
• Shows macOS Security preferences UI
• Has link "Open Security & Privacy Settings"

This is clearly platform-inappropriate for Linux systems.

Environment

• OS: Pop!_OS 22.04 LTS (Ubuntu-based)
• Kernel: 6.17.x
• Keybase Version: 6.5.1
• Desktop Environment: GNOME
• File Manager: Nautilus

Workaround

nautilus /keybase
# or
xdg-open /keybase/private/username

Related Issues

• Client will not open my local file explorer to browser kbfs files #13238 - Client will not open my local file explorer to browse kbfs files (open, 2018)
• Unable to show Files in File Explorer option on Linux #17098 - Unable to show Files in File Explorer option on Linux (closed as regression, 2019)

This appears to be a regression where the Linux code path now incorrectly falls through to macOS-specific UI.

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