feat: expand YouTube playlists into individual queue tracks

_resolve_title replaced with _resolve_tracks using --flat-playlist to
enumerate playlist entries. cmd_play enqueues each track individually,
with truncation when the queue is nearly full. Single-video behavior
unchanged.

tests/test_music.py

@@ -125,7 +125,8 @@ class TestPlayCommand:
     def test_play_queues_track(self):
         bot = _FakeBot()
         msg = _Msg(text="!play https://example.com/track")
-        with patch.object(_mod, "_resolve_title", return_value="Test Track"):
+        tracks = [("https://example.com/track", "Test Track")]
+        with patch.object(_mod, "_resolve_tracks", return_value=tracks):
             with patch.object(_mod, "_ensure_loop"):
                 asyncio.run(_mod.cmd_play(bot, msg))
         assert any("Playing" in r for r in bot.replied)
@@ -140,7 +141,8 @@ class TestPlayCommand:
             url="x", title="Current", requester="Bob",
         )
         msg = _Msg(text="!play https://example.com/next")
-        with patch.object(_mod, "_resolve_title", return_value="Next Track"):
+        tracks = [("https://example.com/next", "Next Track")]
+        with patch.object(_mod, "_resolve_tracks", return_value=tracks):
             asyncio.run(_mod.cmd_play(bot, msg))
         assert any("Queued" in r for r in bot.replied)
 
@@ -152,8 +154,7 @@ class TestPlayCommand:
             for _ in range(_mod._MAX_QUEUE)
         ]
         msg = _Msg(text="!play https://example.com/overflow")
-        with patch.object(_mod, "_resolve_title", return_value="Overflow"):
-            asyncio.run(_mod.cmd_play(bot, msg))
+        asyncio.run(_mod.cmd_play(bot, msg))
         assert any("full" in r.lower() for r in bot.replied)
 
 
@@ -241,7 +242,8 @@ class TestQueueCommand:
     def test_queue_with_url_delegates(self):
         bot = _FakeBot()
         msg = _Msg(text="!queue https://example.com/track")
-        with patch.object(_mod, "_resolve_title", return_value="Title"):
+        tracks = [("https://example.com/track", "Title")]
+        with patch.object(_mod, "_resolve_tracks", return_value=tracks):
             with patch.object(_mod, "_ensure_loop"):
                 asyncio.run(_mod.cmd_queue(bot, msg))
         # Should have called cmd_play logic
@@ -351,3 +353,107 @@ class TestMusicHelpers:
         result = _mod._truncate(long)
         assert len(result) == 80
         assert result.endswith("...")
+
+
+# ---------------------------------------------------------------------------
+# TestPlaylistExpansion
+# ---------------------------------------------------------------------------
+
+
+class TestPlaylistExpansion:
+    def test_enqueue_multiple_tracks(self):
+        bot = _FakeBot()
+        msg = _Msg(text="!play https://example.com/playlist")
+        tracks = [
+            ("https://example.com/1", "Track 1"),
+            ("https://example.com/2", "Track 2"),
+            ("https://example.com/3", "Track 3"),
+        ]
+        with patch.object(_mod, "_resolve_tracks", return_value=tracks):
+            with patch.object(_mod, "_ensure_loop"):
+                asyncio.run(_mod.cmd_play(bot, msg))
+        ps = _mod._ps(bot)
+        assert len(ps["queue"]) == 3
+        assert any("Queued 3 tracks" in r for r in bot.replied)
+
+    def test_truncate_at_queue_limit(self):
+        bot = _FakeBot()
+        ps = _mod._ps(bot)
+        ps["current"] = _mod._Track(url="x", title="Playing", requester="a")
+        # Fill queue to 2 slots remaining
+        ps["queue"] = [
+            _mod._Track(url="x", title="t", requester="a")
+            for _ in range(_mod._MAX_QUEUE - 2)
+        ]
+        msg = _Msg(text="!play https://example.com/playlist")
+        tracks = [
+            ("https://example.com/1", "Track 1"),
+            ("https://example.com/2", "Track 2"),
+            ("https://example.com/3", "Track 3"),
+            ("https://example.com/4", "Track 4"),
+        ]
+        with patch.object(_mod, "_resolve_tracks", return_value=tracks):
+            asyncio.run(_mod.cmd_play(bot, msg))
+        assert len(ps["queue"]) == _mod._MAX_QUEUE
+        assert any("2 of 4" in r for r in bot.replied)
+
+    def test_start_loop_when_idle(self):
+        bot = _FakeBot()
+        msg = _Msg(text="!play https://example.com/playlist")
+        tracks = [
+            ("https://example.com/1", "Track 1"),
+            ("https://example.com/2", "Track 2"),
+        ]
+        with patch.object(_mod, "_resolve_tracks", return_value=tracks):
+            with patch.object(_mod, "_ensure_loop") as mock_loop:
+                asyncio.run(_mod.cmd_play(bot, msg))
+                mock_loop.assert_called_once()
+
+    def test_no_loop_start_when_busy(self):
+        bot = _FakeBot()
+        ps = _mod._ps(bot)
+        ps["current"] = _mod._Track(url="x", title="Current", requester="a")
+        msg = _Msg(text="!play https://example.com/playlist")
+        tracks = [
+            ("https://example.com/1", "Track 1"),
+            ("https://example.com/2", "Track 2"),
+        ]
+        with patch.object(_mod, "_resolve_tracks", return_value=tracks):
+            with patch.object(_mod, "_ensure_loop") as mock_loop:
+                asyncio.run(_mod.cmd_play(bot, msg))
+                mock_loop.assert_not_called()
+
+    def test_resolve_tracks_single_video(self):
+        """Subprocess returning a single url+title pair."""
+        result = MagicMock()
+        result.stdout = "https://example.com/v1\nSingle Video\n"
+        with patch("subprocess.run", return_value=result):
+            tracks = _mod._resolve_tracks("https://example.com/v1")
+        assert tracks == [("https://example.com/v1", "Single Video")]
+
+    def test_resolve_tracks_playlist(self):
+        """Subprocess returning multiple url+title pairs."""
+        result = MagicMock()
+        result.stdout = (
+            "https://example.com/1\nFirst\n"
+            "https://example.com/2\nSecond\n"
+        )
+        with patch("subprocess.run", return_value=result):
+            tracks = _mod._resolve_tracks("https://example.com/pl")
+        assert len(tracks) == 2
+        assert tracks[0] == ("https://example.com/1", "First")
+        assert tracks[1] == ("https://example.com/2", "Second")
+
+    def test_resolve_tracks_error_fallback(self):
+        """On error, returns [(url, url)]."""
+        with patch("subprocess.run", side_effect=Exception("fail")):
+            tracks = _mod._resolve_tracks("https://example.com/bad")
+        assert tracks == [("https://example.com/bad", "https://example.com/bad")]
+
+    def test_resolve_tracks_empty_output(self):
+        """Empty stdout returns fallback."""
+        result = MagicMock()
+        result.stdout = ""
+        with patch("subprocess.run", return_value=result):
+            tracks = _mod._resolve_tracks("https://example.com/empty")
+        assert tracks == [("https://example.com/empty", "https://example.com/empty")]