feat(csm): bootstrap discussion callback flow

plugin/hooks/before-message-write.ts

@@ -25,6 +25,10 @@ type BeforeMessageWriteDeps = {
     content: string,
     logger: { info: (m: string) => void; warn: (m: string) => void },
   ) => Promise<void>;
+  discussionService?: {
+    maybeSendIdleReminder: (channelId: string) => Promise<void>;
+    getDiscussion: (channelId: string) => { status: string } | undefined;
+  };
 };
 
 export function registerBeforeMessageWriteHook(deps: BeforeMessageWriteDeps): void {
@@ -41,6 +45,7 @@ export function registerBeforeMessageWriteHook(deps: BeforeMessageWriteDeps): vo
     ensureTurnOrder,
     resolveDiscordUserId,
     sendModeratorMessage,
+    discussionService,
   } = deps;
 
   api.on("before_message_write", (event, ctx) => {
@@ -164,6 +169,11 @@ export function registerBeforeMessageWriteHook(deps: BeforeMessageWriteDeps): vo
         );
 
         if (!nextSpeaker) {
+          if (discussionService?.getDiscussion(channelId)?.status === "active") {
+            void discussionService.maybeSendIdleReminder(channelId).catch((err) => {
+              api.logger.warn(`dirigent: idle reminder failed: ${String(err)}`);
+            });
+          }
           if (shouldDebugLog(live, channelId)) {
             api.logger.info(`dirigent: before_message_write all agents no-reply, going dormant - no handoff`);
           }