[Fix] Fast misses Slack follow-ups after peer mentions

apps/api/src/handlers/slack/events/fast-agent.ts

@@ -41,6 +41,10 @@ import {
   guardReplyStreamBySourceMessage,
 } from '../helpers/thread-posting.js';
 import { processSlackAttachments } from '../helpers/attachments.js';
+import {
+  mentionsSlackBot,
+  mentionsSlackUserOtherThanBotOrUser,
+} from '../helpers/mention-routing.js';
 
 export async function processFastAgentMessage(params: {
   event: SlackEvent;
@@ -84,6 +88,26 @@ export async function processFastAgentMessage(params: {
   });
 
   const baseQuestion = (event.authoredText ?? event.text).trim();
+  const isDirected =
+    directedAtRoomote || mentionsSlackBot(event, roomoteSlackUserId);
+  const needsPeerCaution =
+    Boolean(roomoteSlackUserId) &&
+    !isDirected &&
+    Boolean(event.user) &&
+    !event.bot_id &&
+    event.subtype !== 'bot_message' &&
+    event.user !== roomoteSlackUserId &&
+    event.channel_type !== 'im' &&
+    event.channel_type !== 'mpim' &&
+    mentionsSlackUserOtherThanBotOrUser(event, roomoteSlackUserId, event.user);
+  const agentContext = needsPeerCaution
+    ? [
+        event.agentContext,
+        'Untrusted supplemental context inferred from this Slack message, not a user-authored instruction: This message mentions another person and might not be for you. Human-to-human interaction may be beginning. From now on in this conversation, unless you are addressed directly (including by name, a reply to you, or a clear contextual follow-up), use ignore_event without sending a reply, reacting, or taking action. When directly addressed, respond normally. This uncertain hint does not override existing instructions.',
+      ]
+        .filter(Boolean)
+        .join('\n\n')
+    : event.agentContext;
 
   // Every Slack round trip from the control plane costs a few hundred
   // milliseconds. Start the thread history lookup as soon as the turn is
@@ -170,6 +194,11 @@ export async function processFastAgentMessage(params: {
         Boolean(message.user) &&
         message.user !== event.user,
     );
+    const allowSilentAmbientReply =
+      event.channel_type !== 'im' &&
+      event.channel_type !== 'mpim' &&
+      !isDirected &&
+      (hasOtherHumanParticipant || needsPeerCaution);
 
     const needsCanonicalAdmission =
       !releaseFastAgentLock ||
@@ -182,12 +211,13 @@ export async function processFastAgentMessage(params: {
       currentMessageId: event.ts,
       userId,
       question,
+      ...(agentContext ? { agentContext } : {}),
       ...(attachments.images.length ? { images: attachments.images } : {}),
       ...(currentMessage?.username
         ? { senderDisplayName: currentMessage.username }
         : {}),
       ...(event.user ? { senderExternalId: event.user } : {}),
-      directedAtRoomote,
+      directedAtRoomote: !allowSilentAmbientReply,
     };
     let durableTurn: FastAgentDurableTurn | null = null;
     if (needsCanonicalAdmission) {
@@ -242,7 +272,7 @@ export async function processFastAgentMessage(params: {
       question,
       images: attachments.images,
       attachmentTexts,
-      currentMessageAgentContext: event.agentContext,
+      currentMessageAgentContext: agentContext,
       threadContext: serializedThreadContext,
       userId,
       apiBaseUrl,
@@ -259,11 +289,7 @@ export async function processFastAgentMessage(params: {
           ? currentMessage.username
           : undefined,
       activeTasks: resolvedActiveTasks,
-      allowSilentAmbientReply:
-        event.channel_type !== 'im' &&
-        event.channel_type !== 'mpim' &&
-        hasOtherHumanParticipant &&
-        !directedAtRoomote,
+      allowSilentAmbientReply,
       ...(roomoteSlackUserId ? { slackRoomoteUserId: roomoteSlackUserId } : {}),
       adapter: {
         createArtifact: (artifact) =>

apps/api/src/handlers/slack/events/message-entry.ts

@@ -142,7 +142,7 @@ type UnmentionedSlackThreadReplyRoutingDecision =
   | { shouldRoute: false }
   | {
       shouldRoute: true;
-      threadMessages: SlackThreadMessage[];
+      threadMessages?: SlackThreadMessage[];
       taskId?: string;
     };
 
@@ -204,6 +204,18 @@ export async function shouldRouteUnmentionedSlackThreadReplyToAgent(params: {
     return { shouldRoute: false };
   }
 
+  // Fast receives the discussion and peer-mention reminders as context;
+  // peer mentions remain an admission cutoff only for legacy task threads.
+  if (
+    await hasBoundSlackFastAgentSession({
+      teamId,
+      channelId: event.channel,
+      threadId: event.thread_ts,
+    })
+  ) {
+    return { shouldRoute: true };
+  }
+
   if (
     mentionsSlackUserOtherThanBotWithoutMentioningBot(
       event,
@@ -216,36 +228,25 @@ export async function shouldRouteUnmentionedSlackThreadReplyToAgent(params: {
   let roomoteThreadMatch: Awaited<
     ReturnType<typeof findRoomoteOwnedSlackThread>
   > | null = null;
-  let isFastAgentThread = false;
 
   let eligibilityReason: 'roomote-owned-thread' | null = null;
 
   {
-    isFastAgentThread = await hasBoundSlackFastAgentSession({
+    roomoteThreadMatch = await findRoomoteOwnedSlackThread({
       teamId,
       channelId: event.channel,
-      threadId: event.thread_ts,
+      threadTs: event.thread_ts,
     });
 
-    roomoteThreadMatch = isFastAgentThread
+    const taskThreadRoute = roomoteThreadMatch
       ? null
-      : await findRoomoteOwnedSlackThread({
-          teamId,
+      : await resolveSlackThreadFollowUpRoute({
+          threadId: event.thread_ts,
           channelId: event.channel,
-          threadTs: event.thread_ts,
+          slackTeamId: teamId,
         });
 
-    const taskThreadRoute =
-      isFastAgentThread || roomoteThreadMatch
-        ? null
-        : await resolveSlackThreadFollowUpRoute({
-            threadId: event.thread_ts,
-            channelId: event.channel,
-            slackTeamId: teamId,
-          });
-
     if (
-      isFastAgentThread ||
       roomoteThreadMatch ||
       (taskThreadRoute && taskThreadRoute.kind !== 'fresh')
     ) {
@@ -314,7 +315,6 @@ export async function shouldRouteUnmentionedSlackThreadReplyToAgent(params: {
     isAutomationReportThread: Boolean(
       roomoteThreadMatch?.isAutomationReportThread,
     ),
-    isOpenConversationThread: isFastAgentThread,
     threadMessages: sharedHistory,
     compareMessageIds: compareNumericMessageIds,
   });

packages/cloud-agents/src/server/fast-agent/fast-agent-service.ts

@@ -2349,6 +2349,7 @@ export async function answerFastAgentQuestion({
           question: followUp.question,
           threadContext: [],
           compatibilityMessages: [],
+          currentMessageAgentContext: followUp.agentContext,
           currentMessageTs: followUp.currentMessageId,
           currentMessageSender: {
             slackUserId: followUp.senderExternalId,