A4: Pin SoulSyncClient observable behavior

5 tests pin the SoulSync standalone client surface — the
structurally-different one (no auth, no API, no library scan).
is_connected just checks os.path.isdir(transfer_path).
ensure_connection reloads config first so the user changing
the transfer_path takes effect without a process restart.
get_all_album_ids returns a set of MD5-hashed string ids
matching cross-server uniform set semantics.

tests/media_server/test_soulsync_pinning.py

@@ -0,0 +1,90 @@
+"""Phase A pinning tests for SoulSyncClient (standalone library mode).
+
+Pin the OBSERVABLE BEHAVIOR the engine will dispatch through.
+SoulSync standalone is the structurally-different one — no auth /
+no API / no library scan. is_connected just checks `transfer_path`
+is a directory. Filesystem walk happens via _get_cached_scan().
+"""
+
+from __future__ import annotations
+
+import os
+from unittest.mock import patch
+
+import pytest
+
+from core.soulsync_client import SoulSyncClient
+
+
+@pytest.fixture
+def ss_client(tmp_path):
+    """A bare SoulSyncClient pointed at a temp directory."""
+    client = SoulSyncClient.__new__(SoulSyncClient)
+    client._transfer_path = str(tmp_path)
+    client._progress_callback = None
+    client._cache = None
+    client._cache_time = 0
+    client._cache_ttl = 300
+    client._last_scan_time = None
+    return client
+
+
+# ---------------------------------------------------------------------------
+# is_connected / ensure_connection
+# ---------------------------------------------------------------------------
+
+
+def test_is_connected_true_when_transfer_path_exists(ss_client, tmp_path):
+    """Pinning: filesystem-based connectivity. is_connected just
+    checks os.path.isdir(transfer_path)."""
+    assert ss_client.is_connected() is True  # tmp_path exists
+
+
+def test_is_connected_false_when_transfer_path_missing(ss_client):
+    """Pinning: missing transfer_path → False. The standalone case
+    where the user hasn't configured a folder yet."""
+    ss_client._transfer_path = '/nonexistent/path/that/does/not/exist'
+    assert ss_client.is_connected() is False
+
+
+def test_ensure_connection_reloads_config_then_checks_path(ss_client, tmp_path):
+    """Pinning: ensure_connection re-reads config (so the user
+    changing the transfer_path takes effect without a process
+    restart) and then checks the path. Returns True iff the path
+    is a directory."""
+    with patch.object(ss_client, '_reload_config') as fake_reload:
+        result = ss_client.ensure_connection()
+
+    fake_reload.assert_called_once()
+    assert result is True
+
+
+# ---------------------------------------------------------------------------
+# get_all_artists / get_all_album_ids
+# ---------------------------------------------------------------------------
+
+
+def test_get_all_artists_uses_cached_scan(ss_client):
+    """Pinning: get_all_artists delegates to _get_cached_scan which
+    enforces the 5-min TTL. Engine extraction must preserve."""
+    fake_artists = [object(), object(), object()]
+    with patch.object(ss_client, '_get_cached_scan', return_value=fake_artists):
+        result = ss_client.get_all_artists()
+    assert result == fake_artists
+
+
+def test_get_all_album_ids_returns_set(ss_client):
+    """Pinning: returns a set of MD5-hashed string ids. Same uniform
+    set semantics as Plex/Jellyfin/Navidrome."""
+    fake_album = type('FakeAlbum', (), {'ratingKey': 'hash-1'})()
+    fake_album2 = type('FakeAlbum', (), {'ratingKey': 'hash-2'})()
+    # Real SoulSyncArtist exposes albums() method (not _albums attr).
+    fake_artist = type('FakeArtist', (), {
+        'albums': lambda self: [fake_album, fake_album2],
+    })()
+
+    with patch.object(ss_client, '_get_cached_scan', return_value=[fake_artist]):
+        result = ss_client.get_all_album_ids()
+
+    assert isinstance(result, set)
+    assert result == {'hash-1', 'hash-2'}