This pull request introduces a robust offline file handling mechanism for the desktop app, allowing files to be stored and accessed locally when offline, while continuing to use signed URLs for online scenarios. The changes span both the frontend and backend, including new APIs, local file post-processing, and a temporary file database. Additionally, there are minor improvements to code style and dependency management.

Offline File Handling and Temporary File Storage:

• Added offline support to the fileToUrl method in HelperState, allowing files to be stored in the app cache and accessed via a local URL when offline. This includes post-processing the file, renaming it by hash, and storing metadata in a new temporaryFilesDb Dexie database. [1] [2] [3]
• Implemented a new Tauri backend command post_process_local_file to hash, rename, and canonicalize locally stored files, ensuring consistent file access and deduplication. [1] [2] [3]

Frontend Integration:

• Updated chat interface and attachment handling to pass and respect the offline flag, ensuring file uploads and attachments work seamlessly in both online and offline modes. [1] [2] [3] [4]

Backend and Utility Improvements:

• Added support for the HTTP HEAD method in the storage backend to enhance interaction with remote storage services.
• Minor code style improvements in several utility files for readability and consistency. [1] [2] [3] [4] [5] [6]

Dependency Updates:

• Added new dependencies (urlencoding, tracing) to the catalog package to support improved logging and URL handling.