refactor: add markdown frontend

src/beaver_gateway/frontends/base.py

@@ -15,13 +15,16 @@ from dataclasses import dataclass, field
 from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
-    from collections.abc import Mapping, Sequence
+    from collections.abc import Awaitable, Callable, Mapping, Sequence
 
     from beaver_gateway.backends.base import Backend
     from beaver_gateway.core.auth import TokenStore
     from beaver_gateway.core.registry import AgentRegistry, McpRegistry
+    from beaver_gateway.core.turn_record import TurnRecord
     from beaver_gateway.storage import Database
 
+    TurnLogHandler = Callable[[TurnRecord], Awaitable[None]]
+
 
 @dataclass(frozen=True, slots=True)
 class GatewayRuntime:
@@ -62,6 +65,18 @@ class GatewayRuntime:
     # the dashboard so the operator can copy ready-to-use links / curl
     # snippets. Other frontends ignore it.
     frontends: Sequence[Frontend] = field(default_factory=tuple)
+    # Frontends that finish a turn (Anthropic Messages, Markdown) iterate
+    # this list and ``await`` each handler with a ``TurnRecord``. Handlers
+    # are appended during ``configure()`` by frontends that want a
+    # cross-frontend chat archive — currently the markdown frontend's
+    # ``log_all_chats`` mode. Handler exceptions are caught at the call
+    # site; they never block the user-visible response.
+    #
+    # The field is typed as ``list[Any]`` rather than the precise
+    # ``list[TurnLogHandler]`` because the alias lives under TYPE_CHECKING
+    # to keep ``anthropic.types`` out of the runtime import graph for
+    # this base module.
+    turn_log_handlers: list[TurnLogHandler] = field(default_factory=list)
 
 
 class Frontend(ABC):