Fix qrexec transport reconnect: blocking waitpid for old child, sync nsigner_client.c with reconnect logic

nostr_core/nsigner_transport.c

@@ -402,10 +402,11 @@ static int nsigner_fd_reconnect_qrexec(nsigner_fd_transport_ctx_t* ctx) {
         return -1;
     }
 
-    /* Reap any previous child */
+    /* Reap any previous child — blocking wait. The parent nsigner_fd_reconnect
+     * already closed the old fds, so the child should have exited. */
     if (ctx->qrexec_pid > 0) {
         int status;
-        (void)waitpid(ctx->qrexec_pid, &status, WNOHANG);
+        (void)waitpid(ctx->qrexec_pid, &status, 0);
         ctx->qrexec_pid = 0;
     }
 
@@ -471,6 +472,7 @@ static int nsigner_fd_reconnect(nsigner_transport_t* t) {
         return -1;
     }
 
+
     ctx = (nsigner_fd_transport_ctx_t*)t->ctx;
 
     /* Close any existing fds first. */