Reuse and clean up temporary thumbnail files

[LostOne1000]

Priority

Medium

Summary

The plug-in creates uniquely named temporary JPEG files but never deletes them.

The current workflow also exports the selected photo more than once:

1. When the dialog opens.
2. Every time Generate is clicked.

Repeated use leaves orphaned files in the system temporary directory.

Relevant code

lightroom-llama.lrplugin/LrLlama.lua

local tempPath =
    LrFileUtils.chooseUniqueFileName(
        LrPathUtils.getStandardFilePath("temp")
            .. "/thumbnail.jpg"
    )

The dialog stores one thumbnail:

local thumbnailPath = exportThumbnail(selectedPhoto)

The Ollama request generates another:

local encodedImage =
    base64EncodeImage(exportThumbnail(photo))

Expected behavior

One generated thumbnail should be reused for the preview and Ollama request, then removed when the dialog context ends.

Implementation notes

• Generate the thumbnail once.
• Pass the path or JPEG data into sendDataToApi().
• Register cleanup through the Lightroom function context.
• Remove the temporary file when:
  • The dialog is saved.
  • The dialog is canceled.
  • An error occurs.
• Log cleanup failures without interrupting the user workflow.

Acceptance criteria

• Opening the dialog creates no more than one temporary thumbnail.
• Repeated Generate operations reuse the existing thumbnail.
• The temporary file is removed when the dialog closes.
• The temporary file is removed following recoverable failures.
• Cleanup errors do not cause metadata loss or dialog failure.