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_readdir.py

@@ -0,0 +1,179 @@
+# -*- coding: utf-8 -*-
+"""Tests for directory listing operations."""
+from __future__ import print_function, unicode_literals
+
+import os
+import unittest
+
+from conftest import BeetFSTestCase
+
+
+class TestReaddirEmpty(BeetFSTestCase):
+    
+    def test_list_empty_root(self):
+        self.mount_beetfs()
+        
+        entries = os.listdir(self.mount_dir)
+        self.assertEqual(entries, [])
+    
+    def test_list_root_returns_list(self):
+        self.mount_beetfs()
+        
+        entries = os.listdir(self.mount_dir)
+        self.assertIsInstance(entries, list)
+
+
+class TestReaddirWithContent(BeetFSTestCase):
+    
+    def setUp(self):
+        super(TestReaddirWithContent, self).setUp()
+        
+        self.add_test_track(
+            filename='track01.flac',
+            artist='Pink Floyd',
+            title='Comfortably Numb',
+            album='The Wall',
+            year='1979',
+            track='01'
+        )
+        self.add_test_track(
+            filename='track02.flac',
+            artist='Pink Floyd',
+            title='Another Brick in the Wall',
+            album='The Wall',
+            year='1979',
+            track='02'
+        )
+        self.add_test_track(
+            filename='track03.flac',
+            artist='Led Zeppelin',
+            title='Stairway to Heaven',
+            album='Led Zeppelin IV',
+            year='1971',
+            track='01'
+        )
+    
+    def test_list_root_shows_artists(self):
+        self.mount_beetfs()
+        
+        entries = os.listdir(self.mount_dir)
+        
+        self.assertIn('Pink Floyd', entries)
+        self.assertIn('Led Zeppelin', entries)
+    
+    def test_list_artist_shows_albums(self):
+        self.mount_beetfs()
+        
+        artist_dir = os.path.join(self.mount_dir, 'Pink Floyd')
+        entries = os.listdir(artist_dir)
+        
+        self.assertTrue(any('The Wall' in e for e in entries))
+    
+    def test_list_album_shows_tracks(self):
+        self.mount_beetfs()
+        
+        artist_dir = os.path.join(self.mount_dir, 'Pink Floyd')
+        albums = os.listdir(artist_dir)
+        wall_album = [a for a in albums if 'The Wall' in a][0]
+        
+        album_dir = os.path.join(artist_dir, wall_album)
+        tracks = os.listdir(album_dir)
+        
+        self.assertEqual(len(tracks), 2)
+    
+    def test_path_format_includes_year(self):
+        self.mount_beetfs()
+        
+        artist_dir = os.path.join(self.mount_dir, 'Pink Floyd')
+        albums = os.listdir(artist_dir)
+        
+        wall_album = [a for a in albums if 'The Wall' in a][0]
+        self.assertIn('1979', wall_album)
+    
+    def test_path_format_includes_format(self):
+        self.mount_beetfs()
+        
+        artist_dir = os.path.join(self.mount_dir, 'Pink Floyd')
+        albums = os.listdir(artist_dir)
+        
+        wall_album = [a for a in albums if 'The Wall' in a][0]
+        self.assertIn('FLAC', wall_album.upper())
+    
+    def test_track_filename_includes_number(self):
+        self.mount_beetfs()
+        
+        artist_dir = os.path.join(self.mount_dir, 'Pink Floyd')
+        albums = os.listdir(artist_dir)
+        wall_album = [a for a in albums if 'The Wall' in a][0]
+        album_dir = os.path.join(artist_dir, wall_album)
+        
+        tracks = os.listdir(album_dir)
+        
+        self.assertTrue(any(t.startswith('01') or t.startswith('1') for t in tracks))
+
+
+class TestReaddirUnicode(BeetFSTestCase):
+    
+    def test_unicode_artist_name(self):
+        self.add_test_track(
+            filename='bjork.flac',
+            artist='Björk',
+            title='Hyperballad',
+            album='Post'
+        )
+        
+        self.mount_beetfs()
+        entries = os.listdir(self.mount_dir)
+        
+        self.assertTrue(
+            any('Bj' in e for e in entries),
+            "Unicode artist name should appear in listing"
+        )
+    
+    def test_unicode_album_name(self):
+        self.add_test_track(
+            filename='sigur.flac',
+            artist='Sigur Ros',
+            title='Hoppipolla',
+            album='Takk...'
+        )
+        
+        self.mount_beetfs()
+        artist_dir = os.path.join(self.mount_dir, 'Sigur Ros')
+        
+        if os.path.isdir(artist_dir):
+            albums = os.listdir(artist_dir)
+            self.assertTrue(len(albums) > 0)
+
+
+class TestReaddirSpecialChars(BeetFSTestCase):
+    
+    def test_artist_with_ampersand(self):
+        self.add_test_track(
+            filename='guns.flac',
+            artist="Guns N' Roses",
+            title='Welcome to the Jungle',
+            album='Appetite for Destruction'
+        )
+        
+        self.mount_beetfs()
+        entries = os.listdir(self.mount_dir)
+        
+        self.assertTrue(len(entries) > 0)
+    
+    def test_title_with_question_mark(self):
+        self.add_test_track(
+            filename='who.flac',
+            artist='The Who',
+            title='Who Are You?',
+            album='Who Are You'
+        )
+        
+        self.mount_beetfs()
+        entries = os.listdir(self.mount_dir)
+        
+        self.assertIn('The Who', entries)
+
+
+if __name__ == '__main__':
+    unittest.main()