refactor: auto-discover channels via pkgutil, eliminate hardcoded registry

nanobot/channels/registry.py

@@ -0,0 +1,35 @@
+"""Auto-discovery for channel modules — no hardcoded registry."""
+
+from __future__ import annotations
+
+import importlib
+import pkgutil
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from nanobot.channels.base import BaseChannel
+
+_INTERNAL = frozenset({"base", "manager", "registry"})
+
+
+def discover_channel_names() -> list[str]:
+    """Return all channel module names by scanning the package (zero imports)."""
+    import nanobot.channels as pkg
+
+    return [
+        name
+        for _, name, ispkg in pkgutil.iter_modules(pkg.__path__)
+        if name not in _INTERNAL and not ispkg
+    ]
+
+
+def load_channel_class(module_name: str) -> type[BaseChannel]:
+    """Import *module_name* and return the first BaseChannel subclass found."""
+    from nanobot.channels.base import BaseChannel as _Base
+
+    mod = importlib.import_module(f"nanobot.channels.{module_name}")
+    for attr in dir(mod):
+        obj = getattr(mod, attr)
+        if isinstance(obj, type) and issubclass(obj, _Base) and obj is not _Base:
+            return obj
+    raise ImportError(f"No BaseChannel subclass in nanobot.channels.{module_name}")