feat: channel plugin architecture with decoupled configs

- Add plugin discovery via Python entry_points (group: nanobot.channels)
- Move 11 channel Config classes from schema.py into their own channel modules
- ChannelsConfig now only keeps send_progress + send_tool_hints (extra=allow)
- Each built-in channel parses dict->Pydantic in __init__, zero internal changes
- All channels implement default_config() for onboard auto-population
- nanobot onboard injects defaults for all discovered channels (built-in + plugins)
- Add nanobot plugins list CLI command
- Add Channel Plugin Guide (docs/CHANNEL_PLUGIN_GUIDE.md)
- Fully backward compatible: existing config.json and sessions work as-is
- 340 tests pass, zero regressions

tests/test_channel_plugins.py

@@ -0,0 +1,225 @@
+"""Tests for channel plugin discovery, merging, and config compatibility."""
+
+from __future__ import annotations
+
+from types import SimpleNamespace
+from unittest.mock import patch
+
+import pytest
+
+from nanobot.bus.events import OutboundMessage
+from nanobot.bus.queue import MessageBus
+from nanobot.channels.base import BaseChannel
+from nanobot.channels.manager import ChannelManager
+from nanobot.config.schema import ChannelsConfig
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+class _FakePlugin(BaseChannel):
+    name = "fakeplugin"
+    display_name = "Fake Plugin"
+
+    async def start(self) -> None:
+        pass
+
+    async def stop(self) -> None:
+        pass
+
+    async def send(self, msg: OutboundMessage) -> None:
+        pass
+
+
+class _FakeTelegram(BaseChannel):
+    """Plugin that tries to shadow built-in telegram."""
+    name = "telegram"
+    display_name = "Fake Telegram"
+
+    async def start(self) -> None:
+        pass
+
+    async def stop(self) -> None:
+        pass
+
+    async def send(self, msg: OutboundMessage) -> None:
+        pass
+
+
+def _make_entry_point(name: str, cls: type):
+    """Create a mock entry point that returns *cls* on load()."""
+    ep = SimpleNamespace(name=name, load=lambda _cls=cls: _cls)
+    return ep
+
+
+# ---------------------------------------------------------------------------
+# ChannelsConfig extra="allow"
+# ---------------------------------------------------------------------------
+
+def test_channels_config_accepts_unknown_keys():
+    cfg = ChannelsConfig.model_validate({
+        "myplugin": {"enabled": True, "token": "abc"},
+    })
+    extra = cfg.model_extra
+    assert extra is not None
+    assert extra["myplugin"]["enabled"] is True
+    assert extra["myplugin"]["token"] == "abc"
+
+
+def test_channels_config_getattr_returns_extra():
+    cfg = ChannelsConfig.model_validate({"myplugin": {"enabled": True}})
+    section = getattr(cfg, "myplugin", None)
+    assert isinstance(section, dict)
+    assert section["enabled"] is True
+
+
+def test_channels_config_builtin_fields_removed():
+    """After decoupling, ChannelsConfig has no explicit channel fields."""
+    cfg = ChannelsConfig()
+    assert not hasattr(cfg, "telegram")
+    assert cfg.send_progress is True
+    assert cfg.send_tool_hints is False
+
+
+# ---------------------------------------------------------------------------
+# discover_plugins
+# ---------------------------------------------------------------------------
+
+_EP_TARGET = "importlib.metadata.entry_points"
+
+
+def test_discover_plugins_loads_entry_points():
+    from nanobot.channels.registry import discover_plugins
+
+    ep = _make_entry_point("line", _FakePlugin)
+    with patch(_EP_TARGET, return_value=[ep]):
+        result = discover_plugins()
+
+    assert "line" in result
+    assert result["line"] is _FakePlugin
+
+
+def test_discover_plugins_handles_load_error():
+    from nanobot.channels.registry import discover_plugins
+
+    def _boom():
+        raise RuntimeError("broken")
+
+    ep = SimpleNamespace(name="broken", load=_boom)
+    with patch(_EP_TARGET, return_value=[ep]):
+        result = discover_plugins()
+
+    assert "broken" not in result
+
+
+# ---------------------------------------------------------------------------
+# discover_all — merge & priority
+# ---------------------------------------------------------------------------
+
+def test_discover_all_includes_builtins():
+    from nanobot.channels.registry import discover_all, discover_channel_names
+
+    with patch(_EP_TARGET, return_value=[]):
+        result = discover_all()
+
+    for name in discover_channel_names():
+        assert name in result
+
+
+def test_discover_all_includes_external_plugin():
+    from nanobot.channels.registry import discover_all
+
+    ep = _make_entry_point("line", _FakePlugin)
+    with patch(_EP_TARGET, return_value=[ep]):
+        result = discover_all()
+
+    assert "line" in result
+    assert result["line"] is _FakePlugin
+
+
+def test_discover_all_builtin_shadows_plugin():
+    from nanobot.channels.registry import discover_all
+
+    ep = _make_entry_point("telegram", _FakeTelegram)
+    with patch(_EP_TARGET, return_value=[ep]):
+        result = discover_all()
+
+    assert "telegram" in result
+    assert result["telegram"] is not _FakeTelegram
+
+
+# ---------------------------------------------------------------------------
+# Manager _init_channels with dict config (plugin scenario)
+# ---------------------------------------------------------------------------
+
+@pytest.mark.asyncio
+async def test_manager_loads_plugin_from_dict_config():
+    """ChannelManager should instantiate a plugin channel from a raw dict config."""
+    from nanobot.channels.manager import ChannelManager
+
+    fake_config = SimpleNamespace(
+        channels=ChannelsConfig.model_validate({
+            "fakeplugin": {"enabled": True, "allowFrom": ["*"]},
+        }),
+        providers=SimpleNamespace(groq=SimpleNamespace(api_key="")),
+    )
+
+    with patch(
+        "nanobot.channels.registry.discover_all",
+        return_value={"fakeplugin": _FakePlugin},
+    ):
+        mgr = ChannelManager.__new__(ChannelManager)
+        mgr.config = fake_config
+        mgr.bus = MessageBus()
+        mgr.channels = {}
+        mgr._dispatch_task = None
+        mgr._init_channels()
+
+    assert "fakeplugin" in mgr.channels
+    assert isinstance(mgr.channels["fakeplugin"], _FakePlugin)
+
+
+@pytest.mark.asyncio
+async def test_manager_skips_disabled_plugin():
+    fake_config = SimpleNamespace(
+        channels=ChannelsConfig.model_validate({
+            "fakeplugin": {"enabled": False},
+        }),
+        providers=SimpleNamespace(groq=SimpleNamespace(api_key="")),
+    )
+
+    with patch(
+        "nanobot.channels.registry.discover_all",
+        return_value={"fakeplugin": _FakePlugin},
+    ):
+        mgr = ChannelManager.__new__(ChannelManager)
+        mgr.config = fake_config
+        mgr.bus = MessageBus()
+        mgr.channels = {}
+        mgr._dispatch_task = None
+        mgr._init_channels()
+
+    assert "fakeplugin" not in mgr.channels
+
+
+# ---------------------------------------------------------------------------
+# Built-in channel default_config() and dict->Pydantic conversion
+# ---------------------------------------------------------------------------
+
+def test_builtin_channel_default_config():
+    """Built-in channels expose default_config() returning a dict with 'enabled': False."""
+    from nanobot.channels.telegram import TelegramChannel
+    cfg = TelegramChannel.default_config()
+    assert isinstance(cfg, dict)
+    assert cfg["enabled"] is False
+    assert "token" in cfg
+
+
+def test_builtin_channel_init_from_dict():
+    """Built-in channels accept a raw dict and convert to Pydantic internally."""
+    from nanobot.channels.telegram import TelegramChannel
+    bus = MessageBus()
+    ch = TelegramChannel({"enabled": False, "token": "test-tok", "allowFrom": ["*"]}, bus)
+    assert ch.config.token == "test-tok"
+    assert ch.config.allow_from == ["*"]