fix: pass accountId to resolveAgentRoute for multi-account routing

The handler was calling resolveAgentRoute without accountId, causing
all Matrix messages to route to the default agent regardless of which
account received them.

Changes:
- Add accountId to MatrixMonitorHandlerParams type
- Extract accountId in createMatrixRoomMessageHandler
- Pass accountId to resolveAgentRoute call
- Pass accountId from monitorMatrixProvider to handler

src/matrix/monitor/handler.ts

@@ -79,6 +79,8 @@ export type MatrixMonitorHandlerParams = {
   };
   getRoomInfo: (roomId: string) => Promise<{ name?: string; canonicalAlias?: string; altAliases: string[] }>;
   getMemberDisplayName: (roomId: string, userId: string) => Promise<string>;
+  /** Account ID for multi-account routing */
+  accountId?: string | null;
 };
 
 export function createMatrixRoomMessageHandler(params: MatrixMonitorHandlerParams) {
@@ -104,6 +106,7 @@ export function createMatrixRoomMessageHandler(params: MatrixMonitorHandlerParam
     directTracker,
     getRoomInfo,
     getMemberDisplayName,
+    accountId,
   } = params;
 
   return async (roomId: string, event: MatrixRawEvent) => {
@@ -442,6 +445,7 @@ export function createMatrixRoomMessageHandler(params: MatrixMonitorHandlerParam
       const route = core.channel.routing.resolveAgentRoute({
         cfg,
         channel: "matrix",
+        accountId: accountId ?? undefined,
         peer: {
           kind: isDirectMessage ? "dm" : "channel",
           id: isDirectMessage ? senderId : roomId,

src/matrix/monitor/index.ts

@@ -223,6 +223,7 @@ export async function monitorMatrixProvider(opts: MonitorMatrixOpts = {}): Promi
     directTracker,
     getRoomInfo,
     getMemberDisplayName,
+    accountId: opts.accountId,
   });
 
   registerMatrixMonitorEvents({