Enhance Downloads Functionality

[ovsky]

This pull request introduces significant improvements to the DownloadManager to enhance reliability, user experience, and persistence of download history. The most notable changes include implementing a robust internal ID mapping system to prevent collisions, adding persistent download history with disk-backed storage, and improving UI logic so completed and failed downloads remain visible until the user clears them. Additionally, new utility methods have been added for encoding/decoding fields and managing history snapshots.

Download ID Management Improvements

• Added an internal ID mapping system (external_to_internal_id_ and related logic) to prevent collisions and ensure downloads are tracked consistently, even if external IDs are reused by Ultralight. This affects download request, begin, finish, fail, and cleanup logic. [1] [2] [3] [4] [5] [6]

Persistent Download History

• Implemented persistent download history: history is loaded from disk on startup (LoadHistoryFromDisk), updated and trimmed on changes, and saved back to disk. This ensures download records are retained across sessions and only a maximum number of entries are kept. [1] [2] [3] [4]

UI and User Experience Enhancements

• Modified UI logic so that completed and failed downloads remain visible until the user explicitly clears them, improving discoverability and allowing users to inspect or retry failed downloads. [1] [2] [3]
• Changed overlay dismissal behavior: the downloads overlay is no longer auto-closed on mouse down outside the overlay, requiring explicit user action to dismiss.

Utility Methods for History Encoding/Decoding

• Added utility methods for encoding and decoding history fields, converting status strings, and handling time points, enabling robust serialization and deserialization of download records. [1] [2]

General Codebase Enhancements

• Added necessary includes (<vector>, <cstdio>) for new functionality.
• Improved thread safety and notification logic by ensuring history is trimmed and updated only when necessary, and the UI is notified of changes appropriately. [1] [2]

Let me know if you want to dive deeper into any specific change!