feat(core,backends,frontends,storage): conversations, inject queue, session pool, gateway mcp tools, api frontend

src/beaver_gateway/core/bus.py

@@ -0,0 +1,69 @@
+"""In-process event bus: what the gateway does, as a stream frontends can tap.
+
+Events are plain dicts ``{"type", "seq", "ts", ...}``. Publishers never
+block; a subscriber that falls behind loses its oldest events rather than
+stalling the turn that produced them. ``/api/events`` serialises the
+stream as SSE, the panel builds its subagent tree from ``stream`` events
+carrying ``parent_tool_use_id``.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import contextlib
+import itertools
+from datetime import UTC, datetime
+from typing import TYPE_CHECKING, Any
+
+if TYPE_CHECKING:
+    from collections.abc import AsyncIterator
+
+__all__ = ["Event", "EventBus"]
+
+Event = dict[str, Any]
+
+
+class EventBus:
+    def __init__(self, *, maxsize: int = 2000) -> None:
+        self._maxsize = maxsize
+        self._subscribers: set[asyncio.Queue[Event]] = set()
+        self._seq = itertools.count(1)
+
+    def publish(self, type_: str, **data: Any) -> Event:
+        event: Event = {
+            "type": type_,
+            "seq": next(self._seq),
+            "ts": datetime.now(UTC).isoformat(timespec="milliseconds"),
+            **data,
+        }
+        for queue in list(self._subscribers):
+            if queue.full():
+                with contextlib.suppress(asyncio.QueueEmpty):
+                    queue.get_nowait()
+            queue.put_nowait(event)
+        return event
+
+    @contextlib.asynccontextmanager
+    async def subscribe(self) -> AsyncIterator[asyncio.Queue[Event]]:
+        queue: asyncio.Queue[Event] = asyncio.Queue(maxsize=self._maxsize)
+        self._subscribers.add(queue)
+        try:
+            yield queue
+        finally:
+            self._subscribers.discard(queue)
+
+    async def stream(
+        self, *, conversation_id: str | None = None
+    ) -> AsyncIterator[Event]:
+        async with self.subscribe() as queue:
+            while True:
+                event = await queue.get()
+                if (
+                    conversation_id is None
+                    or event.get("conversation_id") == conversation_id
+                ):
+                    yield event
+
+    @property
+    def subscribers(self) -> int:
+        return len(self._subscribers)