feat: add !resume to continue playback from last interruption

Tracks playback position via frame counting in stream_audio().
On stop/skip, saves URL + elapsed time to bot.state (SQLite).
!resume reloads the track and seeks to the saved position via
ffmpeg -ss. State persists across bot restarts.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_music.py

@@ -499,3 +499,119 @@ class TestPlaylistExpansion:
         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")]
+
+
+# ---------------------------------------------------------------------------
+# TestResumeState
+# ---------------------------------------------------------------------------
+
+
+class TestResumeState:
+    def test_save_load_roundtrip(self):
+        bot = _FakeBot()
+        track = _mod._Track(url="https://example.com/a", title="Song", requester="Alice")
+        _mod._save_resume(bot, track, 125.5)
+        data = _mod._load_resume(bot)
+        assert data is not None
+        assert data["url"] == "https://example.com/a"
+        assert data["title"] == "Song"
+        assert data["requester"] == "Alice"
+        assert data["elapsed"] == 125.5
+
+    def test_clear_removes_state(self):
+        bot = _FakeBot()
+        track = _mod._Track(url="https://example.com/a", title="Song", requester="Alice")
+        _mod._save_resume(bot, track, 60.0)
+        _mod._clear_resume(bot)
+        assert _mod._load_resume(bot) is None
+
+    def test_load_returns_none_when_empty(self):
+        bot = _FakeBot()
+        assert _mod._load_resume(bot) is None
+
+    def test_load_returns_none_on_corrupt_json(self):
+        bot = _FakeBot()
+        bot.state.set("music", "resume", "not-json{{{")
+        assert _mod._load_resume(bot) is None
+
+    def test_load_returns_none_on_missing_url(self):
+        bot = _FakeBot()
+        bot.state.set("music", "resume", '{"title": "x"}')
+        assert _mod._load_resume(bot) is None
+
+
+# ---------------------------------------------------------------------------
+# TestResumeCommand
+# ---------------------------------------------------------------------------
+
+
+class TestResumeCommand:
+    def test_nothing_saved(self):
+        bot = _FakeBot()
+        msg = _Msg(text="!resume")
+        asyncio.run(_mod.cmd_resume(bot, msg))
+        assert any("Nothing to resume" in r for r in bot.replied)
+
+    def test_already_playing(self):
+        bot = _FakeBot()
+        ps = _mod._ps(bot)
+        ps["current"] = _mod._Track(url="x", title="Playing", requester="a")
+        msg = _Msg(text="!resume")
+        asyncio.run(_mod.cmd_resume(bot, msg))
+        assert any("Already playing" in r for r in bot.replied)
+
+    def test_non_mumble(self):
+        bot = _FakeBot(mumble=False)
+        msg = _Msg(text="!resume")
+        asyncio.run(_mod.cmd_resume(bot, msg))
+        assert any("Mumble-only" in r for r in bot.replied)
+
+    def test_loads_track_and_seeks(self):
+        bot = _FakeBot()
+        track = _mod._Track(url="https://example.com/a", title="Song", requester="Alice")
+        _mod._save_resume(bot, track, 225.0)
+        msg = _Msg(text="!resume")
+        with patch.object(_mod, "_ensure_loop") as mock_loop:
+            asyncio.run(_mod.cmd_resume(bot, msg))
+            mock_loop.assert_called_once_with(bot, seek=225.0)
+        ps = _mod._ps(bot)
+        assert len(ps["queue"]) == 1
+        assert ps["queue"][0].url == "https://example.com/a"
+        assert any("Resuming" in r for r in bot.replied)
+
+    def test_time_format_in_reply(self):
+        bot = _FakeBot()
+        track = _mod._Track(url="https://example.com/a", title="Song", requester="Alice")
+        _mod._save_resume(bot, track, 225.0)
+        msg = _Msg(text="!resume")
+        with patch.object(_mod, "_ensure_loop"):
+            asyncio.run(_mod.cmd_resume(bot, msg))
+        assert any("3:45" in r for r in bot.replied)
+
+    def test_clears_resume_state_after_loading(self):
+        bot = _FakeBot()
+        track = _mod._Track(url="https://example.com/a", title="Song", requester="Alice")
+        _mod._save_resume(bot, track, 60.0)
+        msg = _Msg(text="!resume")
+        with patch.object(_mod, "_ensure_loop"):
+            asyncio.run(_mod.cmd_resume(bot, msg))
+        assert _mod._load_resume(bot) is None
+
+
+# ---------------------------------------------------------------------------
+# TestFmtTime
+# ---------------------------------------------------------------------------
+
+
+class TestFmtTime:
+    def test_zero(self):
+        assert _mod._fmt_time(0) == "0:00"
+
+    def test_seconds_only(self):
+        assert _mod._fmt_time(45) == "0:45"
+
+    def test_minutes_and_seconds(self):
+        assert _mod._fmt_time(225) == "3:45"
+
+    def test_large_value(self):
+        assert _mod._fmt_time(3661) == "61:01"