Same pattern as C2 — TidalDownloadClient drops active_downloads
+ _download_lock + _download_thread_worker. download() delegates
to engine.worker.dispatch with _download_sync as the impl.
Source-specific extras (track_id, display_name) merge into the
engine record.
The HLS-segment progress callback (_update_download_progress)
now writes to engine state via engine.update_record instead of
mutating the per-client dict in-place.
Query/cancel methods (get_all_downloads, get_download_status,
cancel_download, clear_all_completed_downloads) now read engine
state via the same accessors as the YouTube migration.
Pinning tests updated to assert engine state. Suite still green
(313 download tests). Behavior preserved end-to-end.
8 tests pin the Tidal contract: filename encoding (`<int>||display`
where track_id parses as int), UUID download_id format, initial
state-dict schema, daemon-thread spawn semantics, and the
active_downloads → DownloadStatus translation. is_authenticated
false on no-session AND on tidalapi.check_login() exceptions
(orchestrator skip behavior depends on this).
