feat(deploy): per-agent base_url and workspace_path routing

- AgentDefinition gains base_url and workspace_path fields (optional)
- load_agent_registry parses them from matrix-agents.yaml
- _build_platform_from_env uses agent.base_url per agent (falls back to AGENT_BASE_URL)
- _agent_workspace_root() resolves workspace per agent from registry
- _materialize_incoming_attachments saves files to agent workspace_path/incoming/
- send_outgoing accepts workspace_root param; reads outgoing files from agent workspace_path
- dispatch loop computes workspace_root from room agent_id and passes to _send_all
- config/matrix-agents.yaml and example updated with base_url and workspace_path

adapter/matrix/bot.py

@@ -146,10 +146,11 @@ def _build_platform_from_env(*, store: StateStore, chat_mgr: ChatManager) -> Pla
         prototype_state = PrototypeStateStore()
         registry = _load_agent_registry_from_env(required=True)
         assert registry is not None
+        global_base_url = _agent_base_url_from_env()
         delegates = {
             agent.agent_id: RealPlatformClient(
                 agent_id=agent.agent_id,
-                agent_base_url=_agent_base_url_from_env(),
+                agent_base_url=agent.base_url or global_base_url,
                 prototype_state=prototype_state,
                 platform="matrix",
             )
@@ -300,6 +301,8 @@ class MatrixBot:
                 sender,
                 incoming,
             )
+        agent_id = (room_meta or {}).get("agent_id")
+        workspace_root = self._agent_workspace_root(agent_id)
         try:
             outgoing = await self.runtime.dispatcher.dispatch(incoming)
         except PlatformError as exc:
@@ -319,7 +322,7 @@ class MatrixBot:
         else:
             if clear_staged_after_dispatch:
                 await clear_staged_attachments(self.runtime.store, room.room_id, sender)
-        await self._send_all(room.room_id, outgoing)
+        await self._send_all(room.room_id, outgoing, workspace_root=workspace_root)
 
     def _is_file_only_event(
         self, event: RoomMessage, incoming: IncomingMessage | IncomingCommand
@@ -439,13 +442,27 @@ class MatrixBot:
             True,
         )
 
+    def _agent_workspace_root(self, agent_id: str | None) -> Path:
+        default = Path(os.environ.get("SURFACES_WORKSPACE_DIR", "/workspace"))
+        if agent_id is None or self.runtime.registry is None:
+            return default
+        try:
+            agent = self.runtime.registry.get(agent_id)
+            if agent.workspace_path:
+                return Path(agent.workspace_path)
+        except Exception:
+            pass
+        return default
+
     async def _materialize_incoming_attachments(
         self,
         room_id: str,
         matrix_user_id: str,
         incoming: IncomingMessage,
     ) -> IncomingMessage:
-        workspace_root = Path(os.environ.get("SURFACES_WORKSPACE_DIR", "/workspace"))
+        room_meta = await get_room_meta(self.runtime.store, room_id)
+        agent_id = (room_meta or {}).get("agent_id")
+        workspace_root = self._agent_workspace_root(agent_id)
         materialized = []
         for attachment in incoming.attachments:
             materialized.append(
@@ -596,9 +613,20 @@ class MatrixBot:
                 self.runtime.registry,
             )
 
-    async def _send_all(self, room_id: str, outgoing: list[OutgoingEvent]) -> None:
+    async def _send_all(
+        self,
+        room_id: str,
+        outgoing: list[OutgoingEvent],
+        workspace_root: Path | None = None,
+    ) -> None:
         for event in outgoing:
-            await send_outgoing(self.client, room_id, event, store=self.runtime.store)
+            await send_outgoing(
+                self.client,
+                room_id,
+                event,
+                store=self.runtime.store,
+                workspace_root=workspace_root,
+            )
 
 
 async def prepare_live_sync(client: AsyncClient) -> str | None:
@@ -613,6 +641,7 @@ async def send_outgoing(
     room_id: str,
     event: OutgoingEvent,
     store: StateStore | None = None,
+    workspace_root: Path | None = None,
 ) -> None:
     if isinstance(event, OutgoingTyping):
         await client.room_typing(room_id, event.is_typing, timeout=25000)
@@ -627,7 +656,9 @@ async def send_outgoing(
                 room_id, "m.room.message", {"msgtype": "m.text", "body": event.text}
             )
         if event.attachments:
-            workspace_root = Path(os.environ.get("SURFACES_WORKSPACE_DIR", "/workspace"))
+            workspace_root = workspace_root or Path(
+                os.environ.get("SURFACES_WORKSPACE_DIR", "/workspace")
+            )
             for attachment in event.attachments:
                 if not attachment.workspace_path:
                     continue