fix(status): don't re-send pre-transfer call statuses after a transfer (#1584)

A call transferred between feature servers arrives at the receiving server as a
fresh INVITE, so the session runs through trying, ringing, early-media and
answered again as it accepts the REFER. The application was already told all of
that by the server that first handled the call, so it sees a second round of
events for a call it believes is long since answered.

Skip only the application-facing status callback for those four statuses when
the session is a transferred call. callInfo, the redis call record and
record-all-calls still run exactly as before, so the call record stays accurate
and answering a transferred call still starts recording.

Fixes #1392

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

lib/session/call-session.js

@@ -482,6 +482,24 @@ class CallSession extends Emitter {
     return this.application.transferredCall === true;
   }
 
+  /**
+   * returns true if this status was already reported to the application by the feature
+   * server that handled the call before it was transferred here.
+   *
+   * A transferred call arrives as a fresh INVITE, so this session runs through trying,
+   * ringing and answered again as it accepts the REFER. The application has already seen
+   * all of those from the original server, so sending them a second time looks like
+   * duplicate events for a call it believes is long since answered.
+   */
+  _isStatusAlreadyReportedBeforeTransfer(callStatus) {
+    return this.isTransferredCall && [
+      CallStatus.Trying,
+      CallStatus.Ringing,
+      CallStatus.EarlyMedia,
+      CallStatus.InProgress
+    ].includes(callStatus);
+  }
+
   /**
    * returns true if this session is an inbound call session
    */
@@ -3151,7 +3169,16 @@ Duration=${duration} `
       sipReasonHeader ?? reasonHeaderFromSipMessage(msg));
     if (typeof duration === 'number') this.callInfo.duration = duration;
     if (headers) this.callInfo.sipHeaders = headers;
-    this.executeStatusCallback(callStatus, sipStatus);
+
+    /* callInfo and the redis call record are still updated below; only the
+       application-facing notification is skipped */
+    if (this._isStatusAlreadyReportedBeforeTransfer(callStatus)) {
+      this.logger.debug({callStatus},
+        'CallSession:_notifyCallStatusChange - suppressing status already sent before transfer');
+    }
+    else {
+      this.executeStatusCallback(callStatus, sipStatus);
+    }
 
     // update calls db
     //this.logger.debug(`updating redis with ${JSON.stringify(this.callInfo)}`);