Update yt-dlp to 2026.07.04 and refresh the bundled macOS runtime plus engine locks.
Route every non-media download through aria2 by removing the native HTTP fallback path, native GID handling, and the old direct-download harness.
Retry transient aria2 startup/RPC failures before failing, then show the real last error in the download row and Properties modal so Windows failures are diagnosable instead of silent.
Refresh docs and tests around the aria2-only file-download contract, and advance the Firefox extension submodule to its published wording cleanup.
Add aria2 control epochs so delayed resume workers cannot unpause a transfer after a newer pause, remove, or reconfigure command wins.
Thread captured cookies into yt-dlp media runs, sanitize yt-dlp config values, reject malformed media headers, and preserve resumable media artifacts across transient retry backoff.
Cover the new queue epoch and media helper behavior with focused regression tests.
Treat max_tries as the configured retry count instead of total attempts across native, media, aria2, and fallback paths.
Route queue slot acquisition through retirement-aware permit handling so shrinking concurrency does not dispatch new work while active transfers still meet the smaller limit.
Update retry-budget and queue-manager tests to cover the corrected attempt counts and paused aria2 resume behavior.
This commit replaces the frontend-imperative download dispatcher with a centralized backend `QueueManager`. It acts as the sole concurrency gatekeeper using a single `tokio::sync::Semaphore` across all download paths (aria2 RPC, native HTTP, yt-dlp media).
Backend Changes:
- **queue**: Added `QueueManager` to manage an ordered `VecDeque` of tasks, semaphore permits, and retirement debt (CAS resize).
- **commands**: Replaced direct start commands with `enqueue_download`, `enqueue_many`, `move_in_queue`, and `remove_from_queue`.
- **ipc**: Exported `DownloadStateEvent` and `QueueDirection` to the frontend.
- **tests**: Added 11 integration tests covering idle-parking, idempotent releases, CAS underflow prevention, and gid-completion races.
Frontend Changes:
- **store**: Made `useDownloadStore` reactive to the backend via the `download-state` event.
- **store**: Removed `processQueue` and introduced `pendingOrder` to track the accurate sequence of queued items.
- **ui**: Updated `DownloadItem` with queue visuals (clock icon, position badge).
- **ui**: Added Move Up/Down controls to interact with the backend queue reordering API.
NimBold