Improve Exit Error Handling for failures in PASE pairing requests (pr…

…oject-chip#36160)

* Improve Error Handling for failures in PASE pairing requests

* Integrating comments

* clarifying Pair API contract regarding the delegate

* integrating comment on API

src/protocols/secure_channel/PASESession.cpp

@@ -232,7 +232,15 @@ CHIP_ERROR PASESession::Pair(SessionManager & sessionManager, uint32_t peerSetUp
 exit:
     if (err != CHIP_NO_ERROR)
     {
+        // If a failure happens before we have placed the incoming exchange into `mExchangeCtxt`, we need to make
+        // sure to close the exchange to fulfill our API contract.
+        if (!mExchangeCtxt.HasValue())
+        {
+            exchangeCtxt->Close();
+        }
         Clear();
+        ChipLogError(SecureChannel, "Failed during PASE session pairing request: %" CHIP_ERROR_FORMAT, err.Format());
+        MATTER_TRACE_COUNTER("PASEFail");
     }
     return err;
 }

src/protocols/secure_channel/PASESession.h

@@ -99,6 +99,8 @@ class DLL_EXPORT PASESession : public Messaging::UnsolicitedMessageHandler,
      *                            ownership of the exchangeCtxt to PASESession object. PASESession
      *                            will close the exchange on (successful/failed) handshake completion.
      * @param delegate            Callback object
+     *                            The delegate will be notified if and only if Pair() returns success. Errors occurring after Pair()
+     *                            returns success will be reported via the delegate.
      *
      * @return CHIP_ERROR      The result of initialization
      */