feat(voice): Pas 4 — _discord_voice_adapter.py thin layer + contract test

Adapter layer peste vendored discord-ext-voice-recv. Re-exports:
VoiceReceiveClient, AudioSink, VoiceData, plus async helper
connect_voice(channel). Discord voice protocol e fragil, upstream e
hobby fork — dacă pică, swap la py-cord = doar acest fișier rescris.

Contract test (22 assertions) prinde drift la upgrade vendor:
- VoiceReceiveClient methods: connect/disconnect/listen/stop_listening/
  is_listening/stop/cleanup
- listen(sink, *, after=None) signature
- sink property (read/write)
- AudioSink methods: write/cleanup/wants_opus + write(self, user, data) arity
- VoiceData slots (packet/source/pcm) + .opus property

Critical pentru Lane PIPE downstream: write() e called from audio thread
(NOT asyncio loop) — threading primitives mandatory pentru EchoVoiceSink.

22/22 tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_voice_adapter_contract.py

@@ -0,0 +1,171 @@
+# -*- coding: utf-8 -*-
+"""Contract test for `src/voice/_discord_voice_adapter.py`.
+
+Purpose: catch drift when the vendored `discord-ext-voice-recv` is upgraded.
+If upstream renames/removes a method we depend on, this test fails LOUDLY
+before any downstream code breaks at runtime in a Discord voice call.
+
+Per VENDOR_INFO.md: this test MUST PASS after every vendor upgrade.
+
+Plain `import` + `hasattr` / `callable` checks — no mocks. We're verifying
+the SHAPE of the API surface, not behavior.
+"""
+
+from __future__ import annotations
+
+import inspect
+
+import pytest
+
+
+# --- Adapter re-exports import cleanly --------------------------------------
+
+
+def test_adapter_exports_voice_receive_client():
+    from src.voice._discord_voice_adapter import VoiceReceiveClient
+
+    assert VoiceReceiveClient is not None
+    assert inspect.isclass(VoiceReceiveClient)
+
+
+def test_adapter_exports_audio_sink():
+    from src.voice._discord_voice_adapter import AudioSink
+
+    assert AudioSink is not None
+    assert inspect.isclass(AudioSink)
+
+
+def test_adapter_exports_voice_data():
+    from src.voice._discord_voice_adapter import VoiceData
+
+    assert VoiceData is not None
+    assert inspect.isclass(VoiceData)
+
+
+def test_adapter_exports_connect_helper():
+    from src.voice._discord_voice_adapter import connect_voice
+
+    assert callable(connect_voice)
+    assert inspect.iscoroutinefunction(connect_voice)
+
+
+# --- Re-exports point at the real vendored classes (no accidental shadowing) -
+
+
+def test_voice_receive_client_is_voice_recv_client():
+    from discord.ext import voice_recv
+
+    from src.voice._discord_voice_adapter import VoiceReceiveClient
+
+    assert VoiceReceiveClient is voice_recv.VoiceRecvClient
+
+
+def test_audio_sink_is_voice_recv_audio_sink():
+    from discord.ext import voice_recv
+
+    from src.voice._discord_voice_adapter import AudioSink
+
+    assert AudioSink is voice_recv.AudioSink
+
+
+def test_voice_data_is_voice_recv_voice_data():
+    from discord.ext import voice_recv
+
+    from src.voice._discord_voice_adapter import VoiceData
+
+    assert VoiceData is voice_recv.VoiceData
+
+
+# --- VoiceReceiveClient API surface used by the pipeline --------------------
+
+
+@pytest.mark.parametrize(
+    "method_name",
+    [
+        "connect",          # inherited from discord.VoiceClient
+        "disconnect",       # inherited from discord.VoiceClient
+        "listen",           # voice_recv extension
+        "stop_listening",   # voice_recv extension
+        "is_listening",     # voice_recv extension
+        "stop",             # voice_recv extension (stops play+listen)
+        "cleanup",          # voice_recv extension
+    ],
+)
+def test_voice_receive_client_has_method(method_name):
+    from src.voice._discord_voice_adapter import VoiceReceiveClient
+
+    attr = getattr(VoiceReceiveClient, method_name, None)
+    assert attr is not None, f"VoiceReceiveClient is missing `.{method_name}()`"
+    assert callable(attr), f"VoiceReceiveClient.{method_name} is not callable"
+
+
+def test_voice_receive_client_listen_accepts_sink_and_after():
+    """`.listen(sink, *, after=None)` is the canonical call shape."""
+    from src.voice._discord_voice_adapter import VoiceReceiveClient
+
+    sig = inspect.signature(VoiceReceiveClient.listen)
+    params = sig.parameters
+    assert "sink" in params, f"VoiceReceiveClient.listen missing `sink` param; got {list(params)}"
+    assert "after" in params, f"VoiceReceiveClient.listen missing `after` kwarg; got {list(params)}"
+
+
+def test_voice_receive_client_has_sink_property():
+    """`.sink` is read/write so we can swap sinks in place."""
+    from src.voice._discord_voice_adapter import VoiceReceiveClient
+
+    sink_attr = inspect.getattr_static(VoiceReceiveClient, "sink", None)
+    assert isinstance(sink_attr, property), "VoiceReceiveClient.sink must be a property"
+    assert sink_attr.fget is not None, "VoiceReceiveClient.sink property missing getter"
+    assert sink_attr.fset is not None, "VoiceReceiveClient.sink property missing setter"
+
+
+# --- AudioSink API surface --------------------------------------------------
+
+
+@pytest.mark.parametrize(
+    "method_name",
+    [
+        "write",         # write(user, voice_data) — the hot path
+        "cleanup",
+        "wants_opus",    # bool: opus bytes vs decoded PCM
+    ],
+)
+def test_audio_sink_has_method(method_name):
+    from src.voice._discord_voice_adapter import AudioSink
+
+    attr = getattr(AudioSink, method_name, None)
+    assert attr is not None, f"AudioSink is missing `.{method_name}()`"
+    assert callable(attr), f"AudioSink.{method_name} is not callable"
+
+
+def test_audio_sink_write_signature():
+    """`.write(self, user, data)` — user is the speaker (Optional), data is VoiceData."""
+    from src.voice._discord_voice_adapter import AudioSink
+
+    sig = inspect.signature(AudioSink.write)
+    params = list(sig.parameters)
+    # self, user, data
+    assert len(params) >= 3, f"AudioSink.write expected (self, user, data), got {params}"
+
+
+# --- VoiceData attributes ---------------------------------------------------
+
+
+def test_voice_data_slots():
+    """VoiceData uses __slots__ for per-packet allocation. Pipeline reads these."""
+    from src.voice._discord_voice_adapter import VoiceData
+
+    assert hasattr(VoiceData, "__slots__"), "VoiceData lost __slots__ — perf regression risk"
+    slots = set(VoiceData.__slots__)
+    # Documented attributes the pipeline depends on.
+    assert "packet" in slots, f"VoiceData missing `packet` slot; got {slots}"
+    assert "source" in slots, f"VoiceData missing `source` slot (speaker user); got {slots}"
+    assert "pcm" in slots, f"VoiceData missing `pcm` slot (decoded audio); got {slots}"
+
+
+def test_voice_data_has_opus_property():
+    """`.opus` exposes the raw opus bytes from the underlying RTP packet."""
+    from src.voice._discord_voice_adapter import VoiceData
+
+    opus_attr = inspect.getattr_static(VoiceData, "opus", None)
+    assert isinstance(opus_attr, property), "VoiceData.opus must be a property"