Build dtls with records-can-span so the memory BIO example works

Author: aidangarske

.github/examples-manifest.yml

@@ -112,7 +112,7 @@ profiles:
       --enable-static --enable-shared
     # No configure flag for this one; dtls/README.md says to define it so
     # server-dtls13-earlydata can call wolfSSL_dtls13_no_hrr_on_resume().
-    cflags: "-DWOLFSSL_DTLS13_NO_HRR_ON_RESUME"
+    cflags: "-DWOLFSSL_DTLS13_NO_HRR_ON_RESUME -DWOLFSSL_DTLS_RECORDS_CAN_SPAN_DATAGRAMS"
 
   psk:
     flags: "--enable-psk --enable-opensslextra --enable-tls13 --enable-static --enable-shared"
@@ -871,6 +871,9 @@ examples:
       # No dtls server honours any in-band terminator -- "shutdown" does not
       # exist in this dir. Every server loops until SIGINT, so all pairs are
       # server_exit: killed.
+      # BIO_s_mem is a byte stream, so a DTLS record can end mid-read; without
+      # RECORDS_CAN_SPAN_DATAGRAMS (set in the profile) wolfSSL treats that as a
+      # truncated datagram and drops it, and nothing retransmits.
       - exec: [./memory-bio-dtls]
       # A complete DTLS server rather than a self-contained demo: bare exec just
       # blocks in poll() until the step times out. It has no dedicated client.