feat: implement raycast backend

src/beaver_gateway/frontends/base.py

@@ -1,24 +1,46 @@
-"""Frontend ABC.
+"""Frontend ABC + the runtime context handed to ``configure``.
 
 A frontend is anything that listens on a port and routes inbound traffic
-into the agent/MCP registries. ``configure`` is called once after the
-``Gateway`` is built; ``serve`` runs the listening loop.
+into the gateway. ``GatewayRuntime`` carries everything a frontend may
+need that isn't user-config: built registries, per-agent backends, and
+the in-memory token store. The user's ``/config/config.py`` defines a
+``Gateway`` (lists); ``cli.main`` turns that into a ``GatewayRuntime``
+and hands it to each frontend's ``configure``.
 """
 
 from __future__ import annotations
 
 from abc import ABC, abstractmethod
+from dataclasses import dataclass
 from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
-    from beaver_gateway.core.registry import Gateway
+    from beaver_gateway.backends.base import Backend
+    from beaver_gateway.core.auth import TokenStore
+    from beaver_gateway.core.registry import AgentRegistry, McpRegistry
+
+
+@dataclass(frozen=True, slots=True)
+class GatewayRuntime:
+    """Post-build state of the gateway, shared with every frontend.
+
+    Backends are keyed by **agent name**, not type — one ``RaycastBackend``
+    instance can serve many ``RaycastAgent`` instances, but the lookup
+    site (an inbound request with ``model=<agent.name>``) already has
+    the name in hand, so the indirection lives one step earlier.
+    """
+
+    agents: AgentRegistry
+    mcps: McpRegistry
+    backends: dict[str, Backend]
+    token_store: TokenStore
 
 
 class Frontend(ABC):
     """Listens on a port, dispatches into the gateway."""
 
     @abstractmethod
-    def configure(self, gateway: Gateway) -> None: ...
+    def configure(self, runtime: GatewayRuntime) -> None: ...
 
     @abstractmethod
     async def serve(self) -> None: ...