A4: Pin QobuzClient download lifecycle behavior

5 tests pin the Qobuz contract: int track_id parsing, UUID
download_id, state-dict schema (parallels Tidal), daemon-thread
worker target with (download_id, track_id, display_name,
original_filename) signature.

tests/downloads/test_qobuz_pinning.py

@@ -0,0 +1,93 @@
+"""Phase A pinning tests for QobuzClient's download lifecycle.
+
+Qobuz hits the Qobuz REST API + downloads HLS-segmented FLAC.
+Same thread-worker + state-dict pattern as Tidal/HiFi — Phase C
+will lift the threading. These tests pin the contract.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import threading
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+
+from core.qobuz_client import QobuzClient
+
+
+def _run_async(coro):
+    loop = asyncio.new_event_loop()
+    try:
+        return loop.run_until_complete(coro)
+    finally:
+        loop.close()
+
+
+@pytest.fixture
+def qobuz_client():
+    client = QobuzClient.__new__(QobuzClient)
+    client.download_path = Path('./test_qobuz_downloads')
+    client.shutdown_check = None
+    client.active_downloads = {}
+    client._download_lock = threading.Lock()
+    return client
+
+
+def test_download_returns_none_for_invalid_filename_format(qobuz_client):
+    """Pinning: filename without `||` → None, not exception."""
+    result = _run_async(qobuz_client.download('qobuz', 'no-separator', 0))
+    assert result is None
+
+
+def test_download_returns_none_for_non_integer_track_id(qobuz_client):
+    """Pinning: Qobuz REST API uses int track IDs. Non-int → None."""
+    result = _run_async(qobuz_client.download('qobuz', 'not-int||title', 0))
+    assert result is None
+
+
+def test_download_returns_uuid_for_valid_filename(qobuz_client):
+    """Pinning: valid `<int>||display` returns UUID download_id."""
+    with patch('core.qobuz_client.threading.Thread') as fake:
+        fake.return_value.start = lambda: None
+        result = _run_async(qobuz_client.download('qobuz', '12345||Some Song', 0))
+    assert result is not None
+    assert len(result) == 36
+
+
+def test_download_populates_active_downloads_with_initial_state(qobuz_client):
+    """Pinning: per-download record schema for engine extraction."""
+    with patch('core.qobuz_client.threading.Thread') as fake:
+        fake.return_value.start = lambda: None
+        download_id = _run_async(qobuz_client.download('qobuz', '999||My Qobuz Song', 0))
+
+    record = qobuz_client.active_downloads[download_id]
+    assert record['id'] == download_id
+    assert record['filename'] == '999||My Qobuz Song'
+    assert record['username'] == 'qobuz'
+    assert record['state'] == 'Initializing'
+    assert record['progress'] == 0.0
+    assert record['track_id'] == 999
+    assert record['display_name'] == 'My Qobuz Song'
+    assert record['file_path'] is None
+
+
+def test_download_spawns_daemon_thread_targeting_worker(qobuz_client):
+    """Pinning: daemon thread → `_download_thread_worker(download_id, track_id, display_name, original_filename)`."""
+    captured_kwargs = {}
+
+    def capture_thread(*args, **kwargs):
+        captured_kwargs.update(kwargs)
+        return type('FakeThread', (), {'start': lambda self: None})()
+
+    with patch('core.qobuz_client.threading.Thread', side_effect=capture_thread):
+        _run_async(qobuz_client.download('qobuz', '777||Title', 0))
+
+    assert captured_kwargs.get('daemon') is True
+    assert captured_kwargs.get('target') == qobuz_client._download_thread_worker
+    args = captured_kwargs.get('args', ())
+    assert len(args) == 4
+    assert args[1] == 777
+    assert args[2] == 'Title'
+    assert args[3] == '777||Title'