What happened?

A custom theme loaded from a JSON file path can appear in the /theme picker, but selecting/highlighting it by its display name fails with Theme "<name>" not found.

Observed with Catppuccin Mocha on Windows using Gemini CLI 0.39.1.

Initial settings:

{
  "ui": {
    "theme": "C:\\Users\\Admin\\.gemini\\themes\\catppuccin-mocha.json"
  }
}

Theme file contains:

{
  "name": "Catppuccin Mocha",
  "type": "custom",
  "Background": "#1e1e2e",
  "Foreground": "#cdd6f4",
  "LightBlue": "#89dceb",
  "AccentBlue": "#89b4fa",
  "AccentPurple": "#cba6f7",
  "AccentCyan": "#94e2d5",
  "AccentGreen": "#a6e3a1",
  "AccentYellow": "#f9e2af",
  "AccentRed": "#f38ba8",
  "Comment": "#9399b2",
  "Gray": "#7f849c",
  "DiffAdded": "#546d5c",
  "DiffRemoved": "#734a5f",
  "GradientColors": ["#89b4fa", "#cba6f7", "#f38ba8"]
}

Steps to reproduce:

1. Put the theme JSON above at C:\Users\Admin\.gemini\themes\catppuccin-mocha.json.
2. Set ui.theme to the JSON file path.
3. Start Gemini CLI.
4. Open /theme.
5. Highlight/select Catppuccin Mocha.

Result: the picker lists Catppuccin Mocha as a custom theme, but Gemini shows Theme "Catppuccin Mocha" not found.

From inspecting the bundled JS, startup calls themeManager.setActiveTheme(settings.merged.ui.theme), and findThemeByName() loads file themes when the configured value is a path. However, the /theme dialog later calls applyTheme(themeName) with the display/internal name (Catppuccin Mocha). findThemeByName() does not appear to resolve file-loaded themes by their internal name, only by path/canonical path or settings/extension theme keys.

What did you expect to happen?

If a custom theme loaded from a JSON file path is shown in /theme using its internal name, selecting/highlighting that item should activate the theme successfully.

Alternatively, /theme should use the original file path as the value passed to setActiveTheme() for file-loaded themes.

Client information

Platform: Windows, PowerShell Gemini CLI version: 0.39.1 Install path: C:\Users\Admin\.bun\bin\gemini.exe

I did not include /about output because it may contain account/email information.

Login information

Google account OAuth (oauth-personal).

Anything else we need to know?

Workaround: inline the theme under ui.customThemes and set ui.theme to the same key/name:

{
  "ui": {
    "theme": "Catppuccin Mocha",
    "customThemes": {
      "Catppuccin Mocha": {
        "name": "Catppuccin Mocha",
        "type": "custom"
      }
    }
  }
}

With the full color object in ui.customThemes, startup no longer warns and the theme name lookup works.