diff --git a/core/deezer_download_client.py b/core/deezer_download_client.py
index f08f1175..81b0840b 100644
--- a/core/deezer_download_client.py
+++ b/core/deezer_download_client.py
@@ -79,7 +79,10 @@ def _decrypt_chunk(chunk: bytes, key: bytes) -> bytes:
             ) from exc
 
 
-class DeezerDownloadClient:
+from core.download_plugins.base import DownloadSourcePlugin
+
+
+class DeezerDownloadClient(DownloadSourcePlugin):
     """Deezer download client using ARL token authentication."""
 
     def __init__(self, download_path: str = None):
diff --git a/core/download_plugins/__init__.py b/core/download_plugins/__init__.py
index bbe3b8df..ed6a79b6 100644
--- a/core/download_plugins/__init__.py
+++ b/core/download_plugins/__init__.py
@@ -17,9 +17,18 @@ See `core/download_plugins/base.py` for the protocol contract and
 """
 
 from core.download_plugins.base import DownloadSourcePlugin
-from core.download_plugins.registry import DownloadPluginRegistry
+
+# NOTE: DownloadPluginRegistry is intentionally NOT re-exported here.
+# Importing the registry triggers eager imports of every client class
+# (see registry.py for why eager — test fixtures inject mock modules
+# at collection time and we need real bindings before that). Clients
+# inherit from DownloadSourcePlugin (Cin's review feedback — visible
+# contract conformance), so importing the package via ``from
+# core.download_plugins import DownloadSourcePlugin`` from a client
+# file would create a circular import if registry came along for the
+# ride. Callers that need the registry import it directly:
+#     from core.download_plugins.registry import DownloadPluginRegistry
 
 __all__ = [
     "DownloadSourcePlugin",
-    "DownloadPluginRegistry",
 ]
diff --git a/core/download_plugins/base.py b/core/download_plugins/base.py
index f1c7fc0c..5523beeb 100644
--- a/core/download_plugins/base.py
+++ b/core/download_plugins/base.py
@@ -27,12 +27,17 @@ makes the implicit contract explicit so:
 
 from __future__ import annotations
 
-from typing import List, Optional, Protocol, Tuple, runtime_checkable
+from typing import TYPE_CHECKING, List, Optional, Protocol, Tuple, runtime_checkable
 
-# Soulseek client owns the canonical TrackResult / AlbumResult / DownloadStatus
-# dataclasses — every other source already imports from there. Keep it that way
-# until a future PR lifts those into a neutral location.
-from core.soulseek_client import AlbumResult, DownloadStatus, TrackResult
+# Soulseek client owns the canonical TrackResult / AlbumResult /
+# DownloadStatus dataclasses — every other source already imports
+# from there. We only need them for type annotations on this
+# protocol; using TYPE_CHECKING avoids a circular import once the
+# clients themselves inherit from DownloadSourcePlugin (Cin's
+# review feedback — clients explicitly declare conformance instead
+# of relying on structural typing).
+if TYPE_CHECKING:
+    from core.soulseek_client import AlbumResult, DownloadStatus, TrackResult
 
 
 @runtime_checkable
diff --git a/core/hifi_client.py b/core/hifi_client.py
index ea9876de..9a7dfe4c 100644
--- a/core/hifi_client.py
+++ b/core/hifi_client.py
@@ -86,7 +86,10 @@ DEFAULT_INSTANCES = [
 ]
 
 
-class HiFiClient:
+from core.download_plugins.base import DownloadSourcePlugin
+
+
+class HiFiClient(DownloadSourcePlugin):
     """
     HiFi API client for searching and downloading lossless music.
     Uses public hifi-api instances (Tidal backend) — no auth required.
diff --git a/core/lidarr_download_client.py b/core/lidarr_download_client.py
index 8a71b179..0d92cdd9 100644
--- a/core/lidarr_download_client.py
+++ b/core/lidarr_download_client.py
@@ -33,7 +33,10 @@ from core.soulseek_client import TrackResult, AlbumResult, DownloadStatus
 logger = get_logger("lidarr_client")
 
 
-class LidarrDownloadClient:
+from core.download_plugins.base import DownloadSourcePlugin
+
+
+class LidarrDownloadClient(DownloadSourcePlugin):
     """Lidarr download client — uses Lidarr as a download source for Usenet/torrent content.
 
     Implements the same interface as SoulseekClient, QobuzClient, TidalDownloadClient
diff --git a/core/qobuz_client.py b/core/qobuz_client.py
index a06a9031..983dce69 100644
--- a/core/qobuz_client.py
+++ b/core/qobuz_client.py
@@ -104,7 +104,10 @@ QOBUZ_QUALITY_MAP = {
 }
 
 
-class QobuzClient:
+from core.download_plugins.base import DownloadSourcePlugin
+
+
+class QobuzClient(DownloadSourcePlugin):
     """
     Qobuz download client using Qobuz REST API.
     Provides search, matching, and download capabilities as a drop-in alternative to Soulseek/YouTube/Tidal.
diff --git a/core/soulseek_client.py b/core/soulseek_client.py
index e69c9439..bd76b4f9 100644
--- a/core/soulseek_client.py
+++ b/core/soulseek_client.py
@@ -188,7 +188,10 @@ class DownloadStatus:
     time_remaining: Optional[int] = None
     file_path: Optional[str] = None
 
-class SoulseekClient:
+from core.download_plugins.base import DownloadSourcePlugin
+
+
+class SoulseekClient(DownloadSourcePlugin):
     def __init__(self):
         self.base_url: Optional[str] = None
         self.api_key: Optional[str] = None
diff --git a/core/soundcloud_client.py b/core/soundcloud_client.py
index c0362859..0d640985 100644
--- a/core/soundcloud_client.py
+++ b/core/soundcloud_client.py
@@ -82,7 +82,10 @@ def _sanitize_filename(name: str) -> str:
     return cleaned or 'soundcloud_track'
 
 
-class SoundcloudClient:
+from core.download_plugins.base import DownloadSourcePlugin
+
+
+class SoundcloudClient(DownloadSourcePlugin):
     """SoundCloud download client built on yt-dlp's SoundCloud extractor.
 
     Mirrors the public surface of TidalDownloadClient / QobuzClient so the
diff --git a/core/tidal_download_client.py b/core/tidal_download_client.py
index 725a6bee..c2ac6760 100644
--- a/core/tidal_download_client.py
+++ b/core/tidal_download_client.py
@@ -92,7 +92,10 @@ HLS_QUALITY_MAP = {
 HLS_MAP_TAG_RE = re.compile(r'#EXT-X-MAP:.*URI="([^"]+)"')
 
 
-class TidalDownloadClient:
+from core.download_plugins.base import DownloadSourcePlugin
+
+
+class TidalDownloadClient(DownloadSourcePlugin):
     """
     Tidal download client using tidalapi.
     Provides search, matching, and download capabilities as a drop-in alternative to YouTube/Soulseek.
diff --git a/core/youtube_client.py b/core/youtube_client.py
index 3bf0bbe7..b3cd7270 100644
--- a/core/youtube_client.py
+++ b/core/youtube_client.py
@@ -91,7 +91,10 @@ class YouTubeSearchResult:
         self.parsed_artist = self.channel
 
 
-class YouTubeClient:
+from core.download_plugins.base import DownloadSourcePlugin
+
+
+class YouTubeClient(DownloadSourcePlugin):
     """
     YouTube download client using yt-dlp.
     Provides search, matching, and download capabilities with full Spotify metadata integration.