[P6] MLX download failure & 'Malformed URL format' — needs reproduction on rebuilt app

[erickgrau]

What: User reported two runtime errors: "failed to download mlx model" and a "Malformed URL format" message displayed alongside the string "Atomic Chat_1.1.71_aarch64.dmg".

Audit findings:

• The "failed to download mlx model" almost certainly stemmed from the mlx-extension not being installed at all (extensions were never built/bundled — fixed this session). Worth re-testing on the rebuilt app.
• The model-download path was audited: extensions/mlx-extension/src/index.ts builds download items with explicit url/save_path; extensions/download-extension delegates to the Rust core; src-tauri/src/core/downloads/helpers.rs parses URLs defensively (Url::parse with error handling, no naive unwrap on untrusted input). No defect found in a focused review.
• "Malformed URL format" is NOT a string present anywhere in the repo source — likely originates from a dependency or the Tauri layer. It could not be reproduced. The association with the .dmg filename (which contains spaces) suggests something passed a file path/name into a URL parser, possibly via drag-and-drop onto the window (dragDropEnabled is true).

Status: NEEDS REPRODUCTION. Re-test model download on the rebuilt app. If "Malformed URL format" recurs, capture the exact preceding action and the devtools stack trace.

Files: extensions/mlx-extension/src/index.ts, extensions/download-extension/src/index.ts, src-tauri/src/core/downloads/helpers.rs