fix SDES issue for prodigal

lib/call-session.js

@@ -549,6 +549,46 @@ class CallSession extends Emitter {
             localSdpA: async(sdp, res) => {
               this.rtpEngineOpts.uac.tag = res.getParsedHeader('To').params.tag;
 
+              /* HACK (rtcp-mux): some far ends answer an m-line WITHOUT a=rtcp-mux even though
+                 we offered it, advertising a separate RTCP port + a 2nd ICE component they never
+                 service. That dead RTCP component blocks ICE completion and therefore DTLS on that
+                 stream (no SRTP keys -> "no crypto suite negotiated", no audio). Force rtcp-mux back
+                 on every audio m-line and drop the standalone a=rtcp port / component-2 candidates
+                 so rtpengine keeps a single muxed component. */
+              const forceRtcpMux = (sdpStr) => {
+                if (!sdpStr || !sdpStr.includes('m=')) return sdpStr;
+                const eol = sdpStr.includes('\r\n') ? '\r\n' : '\n';
+                const lines = sdpStr.split(/\r?\n/);
+                const result = [];
+                let section = [];
+                let isAudio = false;
+                const flush = () => {
+                  if (!section.length) return;
+                  if (isAudio) {
+                    const hasMux = section.some((l) => l.startsWith('a=rtcp-mux'));
+                    let kept = section.filter((l) => {
+                      if (/^a=rtcp:\d+/.test(l)) return false;            // separate RTCP port
+                      const m = /^a=candidate:\S+\s+(\d+)\s+/.exec(l);     // component 2 == RTCP
+                      if (m && m[1] === '2') return false;
+                      return true;
+                    });
+                    if (!hasMux) kept = [kept[0], 'a=rtcp-mux', ...kept.slice(1)];
+                    result.push(...kept);
+                  } else {
+                    result.push(...section);
+                  }
+                  section = [];
+                };
+                for (const l of lines) {
+                  if (l.startsWith('m=')) { flush(); section = [l]; isAudio = l.startsWith('m=audio'); }
+                  else if (section.length) section.push(l);
+                  else result.push(l);
+                }
+                flush();
+                return result.join(eol);
+              };
+              sdp = forceRtcpMux(sdp);
+
               const opts = {
                 ...this.rtpEngineOpts.common,
                 ...this.rtpEngineOpts.uas.mediaOpts,