diff --git a/core/discovery/quality_scanner.py b/core/discovery/quality_scanner.py
index ebde647c..5a1e424b 100644
--- a/core/discovery/quality_scanner.py
+++ b/core/discovery/quality_scanner.py
@@ -77,6 +77,10 @@ class QualityScannerDeps:
     # so the scan checks against the SAME ranked-target core as the download
     # quality guard — not just the file extension. Injected for testability.
     probe_audio_quality: Callable = None
+    # Resolve a DB-stored (often RELATIVE, e.g. "Artist/Album/Track.flac") path
+    # to an absolute on-disk file by checking the transfer/download/library
+    # dirs. Without this the probe opens a relative path and fails.
+    resolve_library_file_path: Callable = None
 
 
 def _extract_lookup_value(value: Any, *names: str, default: Any = None) -> Any:
@@ -438,14 +442,21 @@ def run_quality_scanner(scope='watchlist', profile_id=1, deps: QualityScannerDep
 
                 # Probe the REAL audio quality (bit depth / sample rate / bitrate)
                 # and check it against the ranked targets — same core as the
-                # download guard. The library path may be a Windows/host path that
-                # needs Docker resolution before mutagen can open it.
-                resolved_path = file_path
-                try:
-                    from core.imports.paths import docker_resolve_path
-                    resolved_path = docker_resolve_path(file_path) if file_path else file_path
-                except Exception:
-                    resolved_path = file_path
+                # download guard. The DB stores paths RELATIVE to the library root
+                # (e.g. "Artist/Album/Track.flac"), so resolve to an absolute
+                # on-disk path first or mutagen can't open the file.
+                resolved_path = None
+                if deps.resolve_library_file_path:
+                    try:
+                        resolved_path = deps.resolve_library_file_path(file_path)
+                    except Exception:
+                        resolved_path = None
+                if not resolved_path:
+                    try:
+                        from core.imports.paths import docker_resolve_path
+                        resolved_path = docker_resolve_path(file_path) if file_path else file_path
+                    except Exception:
+                        resolved_path = file_path
 
                 aq = deps.probe_audio_quality(resolved_path) if deps.probe_audio_quality else None
                 if aq is not None:
diff --git a/tests/discovery/test_discovery_quality_scanner.py b/tests/discovery/test_discovery_quality_scanner.py
index bec7fa49..0841fec8 100644
--- a/tests/discovery/test_discovery_quality_scanner.py
+++ b/tests/discovery/test_discovery_quality_scanner.py
@@ -175,6 +175,7 @@ def _build_deps(
         get_quality_tier_from_extension=lambda fp: quality_tier_result,
         add_activity_item=lambda *a, **kw: None,
         probe_audio_quality=probe_fn or _default_probe,
+        resolve_library_file_path=lambda fp: fp,  # identity — tests use direct paths
     )
     return deps
 
@@ -263,6 +264,30 @@ def test_high_quality_tracks_skipped(mock_db_and_wishlist):
     assert state['low_quality'] == 0
 
 
+def test_scanner_resolves_relative_path_before_probing(mock_db_and_wishlist):
+    """DB stores RELATIVE paths (Artist/Album/Track.flac); the scanner must
+    resolve them to absolute via resolve_library_file_path before probing,
+    otherwise mutagen can't open the file and the whole library passes."""
+    from core.quality.model import AudioQuality
+
+    db, _ = mock_db_and_wishlist
+    db._watchlist_artists = [_WatchlistArtist('A')]
+    db._tracks = [_track_row(file_path='Artist/Album/Track.flac')]
+    state = {}
+    probed = []
+
+    def _probe(fp):
+        probed.append(fp)
+        return AudioQuality('flac', bit_depth=16, sample_rate=44100)
+
+    deps = _build_deps(state=state, probe_fn=_probe)
+    deps.resolve_library_file_path = lambda fp: '/music/' + fp
+
+    qs.run_quality_scanner('watchlist', 1, deps)
+
+    assert probed == ['/music/Artist/Album/Track.flac']
+
+
 def test_low_quality_tracks_attempted(mock_db_and_wishlist):
     """Low-quality tracks (tier_num > min) trigger a metadata search."""
     db, _ = mock_db_and_wishlist
diff --git a/web_server.py b/web_server.py
index 620114a8..f68277ee 100644
--- a/web_server.py
+++ b/web_server.py
@@ -17662,6 +17662,7 @@ def _build_quality_scanner_deps():
         get_quality_tier_from_extension=_get_quality_tier_from_extension,
         add_activity_item=add_activity_item,
         probe_audio_quality=_probe_audio_quality,
+        resolve_library_file_path=_resolve_library_file_path,
     )