Add e2e test suite for beetfs

Tests use real FUSE operations against mounted beetfs filesystem:
- test_smoke: mount/unmount lifecycle
- test_nested_bug: detects critical indentation bug (13 failures)
- test_readdir: directory listing
- test_read: metadata overlay verification
- test_stat: file/directory attributes
- test_write: metadata modification
- test_error_handling: ENOENT, EOPNOTSUPP

Also includes:
- conftest.py with BeetFSTestCase base class and synthetic FLAC generator
- e2e-test-plan.md with Oracle-reviewed test strategy
- flake.nix updated with ffmpeg/flac for test fixtures

Run: cd tests && nix develop ../ --command python -m unittest discover

tests/test_stat.py

@@ -0,0 +1,138 @@
+# -*- coding: utf-8 -*-
+from __future__ import print_function, unicode_literals
+
+import os
+import stat
+import unittest
+
+from conftest import BeetFSTestCase
+
+
+class TestStatFile(BeetFSTestCase):
+    
+    def setUp(self):
+        super(TestStatFile, self).setUp()
+        self.file_path, self.item_id = self.add_test_track(
+            filename='stat_test.flac',
+            artist='Test Artist',
+            title='Test Track',
+            album='Test Album'
+        )
+    
+    def test_stat_returns_stat_result(self):
+        self.mount_beetfs()
+        
+        tracks = self._find_any_track()
+        if not tracks:
+            self.skipTest("No tracks found")
+        
+        result = os.stat(tracks[0])
+        self.assertTrue(hasattr(result, 'st_mode'))
+        self.assertTrue(hasattr(result, 'st_size'))
+    
+    def test_stat_file_mode(self):
+        self.mount_beetfs()
+        
+        tracks = self._find_any_track()
+        if not tracks:
+            self.skipTest("No tracks found")
+        
+        result = os.stat(tracks[0])
+        self.assertTrue(stat.S_ISREG(result.st_mode))
+    
+    def test_stat_file_size_positive(self):
+        self.mount_beetfs()
+        
+        tracks = self._find_any_track()
+        if not tracks:
+            self.skipTest("No tracks found")
+        
+        result = os.stat(tracks[0])
+        self.assertGreater(result.st_size, 0)
+    
+    def test_stat_file_size_matches_original(self):
+        original_size = os.path.getsize(self.file_path)
+        
+        self.mount_beetfs()
+        
+        tracks = self._find_any_track()
+        if not tracks:
+            self.skipTest("No tracks found")
+        
+        result = os.stat(tracks[0])
+        self.assertAlmostEqual(result.st_size, original_size, delta=original_size * 0.5)
+    
+    def _find_any_track(self):
+        results = []
+        for root, dirs, files in os.walk(self.mount_dir):
+            for f in files:
+                if f.endswith('.flac'):
+                    results.append(os.path.join(root, f))
+        return results
+
+
+class TestStatDirectory(BeetFSTestCase):
+    
+    def test_stat_root(self):
+        self.mount_beetfs()
+        
+        result = os.stat(self.mount_dir)
+        self.assertTrue(stat.S_ISDIR(result.st_mode))
+    
+    def test_stat_artist_directory(self):
+        self.add_test_track(
+            filename='test.flac',
+            artist='Stat Test Artist'
+        )
+        
+        self.mount_beetfs()
+        
+        artist_dir = os.path.join(self.mount_dir, 'Stat Test Artist')
+        if os.path.isdir(artist_dir):
+            result = os.stat(artist_dir)
+            self.assertTrue(stat.S_ISDIR(result.st_mode))
+
+
+class TestStatfs(BeetFSTestCase):
+    
+    def test_statvfs_returns_result(self):
+        self.mount_beetfs()
+        
+        result = os.statvfs(self.mount_dir)
+        self.assertTrue(hasattr(result, 'f_bsize'))
+        self.assertTrue(hasattr(result, 'f_blocks'))
+
+
+class TestAccess(BeetFSTestCase):
+    
+    def test_access_root_readable(self):
+        self.mount_beetfs()
+        
+        self.assertTrue(os.access(self.mount_dir, os.R_OK))
+    
+    def test_access_root_executable(self):
+        self.mount_beetfs()
+        
+        self.assertTrue(os.access(self.mount_dir, os.X_OK))
+    
+    def test_access_file_readable(self):
+        self.add_test_track(filename='access_test.flac')
+        self.mount_beetfs()
+        
+        tracks = self._find_any_track()
+        if not tracks:
+            self.skipTest("No tracks found")
+        
+        self.assertTrue(os.access(tracks[0], os.R_OK))
+    
+    def _find_any_track(self):
+        results = []
+        for root, dirs, files in os.walk(self.mount_dir):
+            for f in files:
+                if f.endswith('.flac'):
+                    results.append(os.path.join(root, f))
+        return results
+
+
+if __name__ == '__main__':
+    unittest.main()