echoserver: keep the EOF reply owed across a rekey

wolfSSH_ChannelIdRead() has no rekey guard, so a drained channel still
reports zero mid-rekey and the drain loop calls the reply in. That send
returns WS_REKEYING before it prepares a packet, so nothing is queued.

- take the send's status instead of discarding it
- latch eofAnswered and ChildRunning on every status but WS_REKEYING, so
  the reply is retried on a later pass; the KEX traffic wakes it
- a short send is left latching: it bundled the EOF and set eofTxd, so a
  retry queues nothing and the loop would stall in an untimed select
  waiting on a peer that has already half-closed
- same change in the Espressif copy

examples/echoserver/echoserver.c

@@ -1067,9 +1067,16 @@ static int ssh_worker(thread_ctx_t* threadCtx)
                         /* Only an emptied channel earns the EOF; anything
                          * else is retried on a later pass. */
                         if (eofDrained) {
-                            wolfSSH_ChannelSendEof(eofChannel);
-                            eofAnswered = 1;
-                            ChildRunning = 0;
+                            int eofRet;
+
+                            eofRet = wolfSSH_ChannelSendEof(eofChannel);
+                            /* A rekey queues nothing, so the reply is still
+                             * owed and the KEX traffic wakes the next pass.
+                             * A short send already bundled it. */
+                            if (eofRet != WS_REKEYING) {
+                                eofAnswered = 1;
+                                ChildRunning = 0;
+                            }
                         }
                     }
                 }

ide/Espressif/ESP-IDF/examples/wolfssh_echoserver/main/echoserver.c

@@ -1051,9 +1051,16 @@ static int ssh_worker(thread_ctx_t* threadCtx)
                         /* Only an emptied channel earns the EOF; anything
                          * else is retried on a later pass. */
                         if (eofDrained) {
-                            wolfSSH_ChannelSendEof(eofChannel);
-                            eofAnswered = 1;
-                            ChildRunning = 0;
+                            int eofRet;
+
+                            eofRet = wolfSSH_ChannelSendEof(eofChannel);
+                            /* A rekey queues nothing, so the reply is still
+                             * owed and the KEX traffic wakes the next pass.
+                             * A short send already bundled it. */
+                            if (eofRet != WS_REKEYING) {
+                                eofAnswered = 1;
+                                ChildRunning = 0;
+                            }
                         }
                     }
                 }