fix(mates): restore mention indicator state across view switches and DOM rebuilds

Track active mention mateId server-side and re-send mention_processing on
session switch. Cache mention-active state client-side so renderUserStrip DOM
rebuilds preserve the processing dot and blink animation.

Author: leiyangyou

lib/project-mate-interaction.js

@@ -445,6 +445,7 @@ function attachMateInteraction(ctx) {
     }
 
     session._mentionInProgress = true;
+    session._mentionActiveMateId = msg.mateId;
 
     // Send mention start indicator
     sendToSession(session.localId, {
@@ -478,6 +479,7 @@ function attachMateInteraction(ctx) {
       },
       onDone: function (fullText) {
         session._mentionInProgress = false;
+        session._mentionActiveMateId = null;
 
         // Save mention response to session history
         var mentionResponseEntry = {
@@ -512,6 +514,7 @@ function attachMateInteraction(ctx) {
       },
       onError: function (errMsg) {
         session._mentionInProgress = false;
+        session._mentionActiveMateId = null;
         // Clean up dead session
         if (session._mentionSessions && session._mentionSessions[msg.mateId]) {
           delete session._mentionSessions[msg.mateId];
@@ -610,6 +613,7 @@ function attachMateInteraction(ctx) {
         }
       }).catch(function (err) {
         session._mentionInProgress = false;
+        session._mentionActiveMateId = null;
         console.error("[mention] Failed to create session for mate " + msg.mateId + ":", err.message || err);
         sendToSession(session.localId, { type: "mention_error", mateId: msg.mateId, error: "Failed to create mention session." });
       });

lib/project.js

@@ -624,6 +624,7 @@ function createProjectContext(opts) {
           delete session._mentionSessions[mateId];
         }
         session._mentionInProgress = false;
+        session._mentionActiveMateId = null;
         sendToSession(session.localId, { type: "mention_done", mateId: mateId, stopped: true });
         send({ type: "mention_processing", mateId: mateId, active: false });
       }