Updates to fix fallout from #19502.

We need to allow messages on inactive sessions to reach the exchange manager,
because such sessions need to be able to deliver an MRP ack to an exchange
waiting for one.

We also don't want to crash on an attempt to transition from Inactive to Defunct
state; the transition should just be ignored.  This way if we start trying to
transitionin to Defunct on MRP delivery failures we will not start crashing if
such a failure happens on an Inactive session.

src/messaging/ExchangeMgr.cpp

@@ -236,7 +236,13 @@ void ExchangeManager::OnMessageReceived(const PacketHeader & packetHeader, const
                         packetHeader.GetDestinationGroupId().Value());
     }
 
-    // Do not handle unsolicited messages on a inactive session.
+    // Do not handle messages that don't match an existing exchange on a
+    // inactive session, since we should not be creating new exchanges there.
+    if (!session->IsActiveSession()) {
+        ChipLogProgress(ExchangeManager, "Dropping message on inactive session that does not match an existing exchange");
+        return;
+    }
+
     // If it's not a duplicate message, search for an unsolicited message handler if it is marked as being sent by an initiator.
     // Since we didn't find an existing exchange that matches the message, it must be an unsolicited message. However all
     // unsolicited messages must be marked as being from an initiator.

src/transport/SecureSession.cpp

@@ -46,6 +46,10 @@ const char * SecureSession::StateToString(State state) const
         return "kPendingEviction";
         break;
 
+    case State::kInactive:
+        return "kInactive";
+        break;
+
     default:
         return "???";
         break;
@@ -89,9 +93,12 @@ void SecureSession::MarkAsDefunct()
 
     case State::kInactive:
         //
-        // Once a session is marked Inactive, we CANNOT bring it back to either being active or defunct.
+        // Once a session is marked Inactive, we CANNOT bring it back to either
+        // being active or defunct.  But consumers may not really know this
+        // session is already inactive.  Just ignore the call and stay in
+        // kInactive state.
         //
-        FALLTHROUGH;
+        return;
     case State::kPendingEviction:
         //
         // Once a session is headed for eviction, we CANNOT bring it back to either being active or defunct.

src/transport/SecureSession.h

@@ -144,6 +144,7 @@ class SecureSession : public Session, public ReferenceCounted<SecureSession, Sec
     bool IsEstablishing() const { return mState == State::kEstablishing; }
     bool IsPendingEviction() const { return mState == State::kPendingEviction; }
     bool IsDefunct() const { return mState == State::kDefunct; }
+    bool IsInactive() const { return mState == State::kInactive; }
     const char * GetStateStr() const { return StateToString(mState); }
 
     /*

src/transport/SessionManager.cpp

@@ -532,7 +532,7 @@ void SessionManager::SecureUnicastMessageDispatch(const PacketHeader & packetHea
 
     Transport::SecureSession * secureSession = session.Value()->AsSecureSession();
 
-    if (!secureSession->IsDefunct() && !secureSession->IsActiveSession())
+    if (!secureSession->IsDefunct() && !secureSession->IsActiveSession() && !secureSession->IsInactive())
     {
         ChipLogError(Inet, "Secure transport received message on a session in an invalid state (state = '%s')",
                      secureSession->GetStateStr());