feat: support relative volume adjustment (+N/-N)

!volume +10 increases by 10, !volume -5 decreases by 5.
Out-of-range results (below 0 or above 100) are rejected.

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

plugins/music.py

@@ -405,13 +405,14 @@ async def cmd_testtone(bot, message):
     await bot.reply(message, "Test tone complete")
 
 
-@command("volume", help="Music: !volume [0-100]")
+@command("volume", help="Music: !volume [0-100|+N|-N]")
 async def cmd_volume(bot, message):
     """Get or set playback volume.
 
     Usage:
         !volume         Show current volume
         !volume <0-100> Set volume (takes effect immediately)
+        !volume +N/-N   Adjust volume relatively
     """
     if not _is_mumble(bot):
         return
@@ -422,12 +423,18 @@ async def cmd_volume(bot, message):
         await bot.reply(message, f"Volume: {ps['volume']}%")
         return
 
+    arg = parts[1].strip()
+    relative = arg.startswith("+") or (arg.startswith("-") and arg != "-")
+
     try:
-        val = int(parts[1])
+        val = int(arg)
     except ValueError:
-        await bot.reply(message, "Usage: !volume <0-100>")
+        await bot.reply(message, "Usage: !volume <0-100|+N|-N>")
         return
 
+    if relative:
+        val = ps["volume"] + val
+
     if val < 0 or val > 100:
         await bot.reply(message, "Volume must be 0-100")
         return

tests/test_music.py

@@ -319,8 +319,41 @@ class TestVolumeCommand:
         asyncio.run(_mod.cmd_volume(bot, msg))
         assert any("0-100" in r for r in bot.replied)
 
-    def test_volume_negative(self):
+    def test_volume_negative_absolute(self):
+        """Bare negative that underflows clamps at 0-100 error."""
         bot = _FakeBot()
+        _mod._ps(bot)["volume"] = 5
+        msg = _Msg(text="!volume -10")
+        asyncio.run(_mod.cmd_volume(bot, msg))
+        assert any("0-100" in r for r in bot.replied)
+
+    def test_volume_relative_up(self):
+        bot = _FakeBot()
+        msg = _Msg(text="!volume +15")
+        asyncio.run(_mod.cmd_volume(bot, msg))
+        ps = _mod._ps(bot)
+        assert ps["volume"] == 65
+        assert any("65%" in r for r in bot.replied)
+
+    def test_volume_relative_down(self):
+        bot = _FakeBot()
+        _mod._ps(bot)["volume"] = 80
+        msg = _Msg(text="!volume -20")
+        asyncio.run(_mod.cmd_volume(bot, msg))
+        ps = _mod._ps(bot)
+        assert ps["volume"] == 60
+        assert any("60%" in r for r in bot.replied)
+
+    def test_volume_relative_clamp_over(self):
+        bot = _FakeBot()
+        _mod._ps(bot)["volume"] = 95
+        msg = _Msg(text="!volume +10")
+        asyncio.run(_mod.cmd_volume(bot, msg))
+        assert any("0-100" in r for r in bot.replied)
+
+    def test_volume_relative_clamp_under(self):
+        bot = _FakeBot()
+        _mod._ps(bot)["volume"] = 5
         msg = _Msg(text="!volume -10")
         asyncio.run(_mod.cmd_volume(bot, msg))
         assert any("0-100" in r for r in bot.replied)