feat: add Pydantic models and EventEmitter for v2 core

- models.py: ProviderConfig, RoleConfig, DiscussionConfig, ScenarioConfig,
  Message, ToolCallRecord, Session — compatible with config.yaml format
- events.py: Event constants, Event dataclass, EventEmitter with on/off/emit
- 67 tests passing (37 models + 30 events)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

meeting_room/events.py

@@ -0,0 +1,129 @@
+"""EventEmitter and event types for the Meeting Room discussion engine.
+
+Synchronous event bus. In Phase 2, an AsyncEventBridge will forward
+events to WebSocket clients.
+"""
+
+from __future__ import annotations
+
+import logging
+from dataclasses import dataclass, field
+from datetime import datetime
+from typing import Any, Callable
+
+logger = logging.getLogger(__name__)
+
+# ---------------------------------------------------------------------------
+# Event type constants
+# ---------------------------------------------------------------------------
+
+DISCUSSION_START = "discussion_start"
+ROUND_START = "round_start"
+AGENT_TURN_START = "agent_turn_start"
+AGENT_MESSAGE = "agent_message"
+TOOL_CALL = "tool_call"
+TOOL_RESULT = "tool_result"
+AGENT_ERROR = "agent_error"
+ROUND_END = "round_end"
+DISCUSSION_END = "discussion_end"
+BOSS_TURN = "boss_turn"
+
+# ---------------------------------------------------------------------------
+# Event dataclass
+# ---------------------------------------------------------------------------
+
+
+@dataclass
+class Event:
+    """A single event emitted by the discussion engine."""
+
+    type: str
+    data: dict[str, Any] = field(default_factory=dict)
+    timestamp: datetime = field(default_factory=datetime.now)
+
+
+# ---------------------------------------------------------------------------
+# EventEmitter
+# ---------------------------------------------------------------------------
+
+# Type alias for handler callbacks
+Handler = Callable[[Event], None]
+
+
+class EventEmitter:
+    """Synchronous pub/sub event bus.
+
+    Usage::
+
+        bus = EventEmitter()
+
+        def on_message(event: Event):
+            print(event.data)
+
+        bus.on(AGENT_MESSAGE, on_message)
+        bus.emit(AGENT_MESSAGE, text="Hello", agent="Alice")
+        bus.off(AGENT_MESSAGE, on_message)
+    """
+
+    def __init__(self) -> None:
+        self._handlers: dict[str, list[Handler]] = {}
+
+    # -- subscription --------------------------------------------------------
+
+    def on(self, event_type: str, handler: Handler) -> Handler:
+        """Subscribe *handler* to *event_type*.
+
+        Returns the handler so callers can use ``off`` with the same
+        reference, or chain calls.
+        """
+        self._handlers.setdefault(event_type, []).append(handler)
+        return handler
+
+    def off(self, event_type: str, handler: Handler) -> None:
+        """Unsubscribe *handler* from *event_type*.
+
+        Silently ignores unknown event types or missing handlers.
+        """
+        handlers = self._handlers.get(event_type)
+        if handlers is None:
+            return
+        try:
+            handlers.remove(handler)
+        except ValueError:
+            pass
+        # Clean up empty lists to avoid unbounded growth
+        if not handlers:
+            del self._handlers[event_type]
+
+    # -- emission ------------------------------------------------------------
+
+    def emit(self, event_type: str, **data: Any) -> Event:
+        """Create an Event and call every subscribed handler synchronously.
+
+        Handlers that raise exceptions are caught and logged; the emitter
+        never crashes due to a bad handler.
+
+        Returns the Event that was emitted (useful for testing).
+        """
+        event = Event(type=event_type, data=data)
+        handlers = self._handlers.get(event_type, [])
+        for handler in handlers:
+            try:
+                handler(event)
+            except Exception:
+                logger.exception(
+                    "Handler %r raised for event %s",
+                    handler,
+                    event_type,
+                )
+        return event
+
+    # -- introspection -------------------------------------------------------
+
+    def handlers(self, event_type: str) -> list[Handler]:
+        """Return a *copy* of the handler list for *event_type*."""
+        return list(self._handlers.get(event_type, []))
+
+    def clear(self) -> None:
+        """Remove all subscriptions."""
+        self._handlers.clear()