[feat](trx-frontend-http): consume server-side APRS/CW decode via SSE

Add /decode SSE endpoint streaming decoded messages from the server.
Add decode channel OnceLock with set/subscribe pattern.

In the browser, connect to /decode EventSource and dispatch to
onServerAprs/onServerCw handlers.  APRS and CW plugins now receive
server-decoded data automatically while keeping browser-side decoding
as a fallback.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js

@@ -1122,6 +1122,30 @@ volWheel(txVolSlider, txVolPct, () => txGainNode, "txVol");
 
 document.getElementById("copyright-year").textContent = new Date().getFullYear();
 
+// --- Server-side decode SSE ---
+let decodeSource = null;
+let decodeConnected = false;
+function connectDecode() {
+  if (decodeSource) { decodeSource.close(); }
+  decodeSource = new EventSource("/decode");
+  decodeSource.onopen = () => { decodeConnected = true; };
+  decodeSource.onmessage = (evt) => {
+    try {
+      const msg = JSON.parse(evt.data);
+      if (msg.type === "aprs" && window.onServerAprs) window.onServerAprs(msg);
+      if (msg.type === "cw" && window.onServerCw) window.onServerCw(msg);
+    } catch (e) {
+      // ignore parse errors
+    }
+  };
+  decodeSource.onerror = () => {
+    decodeSource.close();
+    decodeConnected = false;
+    setTimeout(connectDecode, 5000);
+  };
+}
+connectDecode();
+
 // Release PTT on page unload to prevent stuck transmit
 window.addEventListener("beforeunload", () => {
   if (txActive) {

src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/aprs.js

@@ -643,7 +643,34 @@ for (let i = aprsPacketHistory.length - 1; i >= 0; i--) {
   }
 }
 
-// Auto-start APRS if it was running before page refresh
+// --- Server-side APRS decode handler ---
+window.onServerAprs = function(pkt) {
+  addAprsPacket({
+    srcCall: pkt.src_call,
+    destCall: pkt.dest_call,
+    path: pkt.path,
+    info: pkt.info,
+    type: pkt.packet_type,
+    crcOk: pkt.crc_ok,
+    lat: pkt.lat,
+    lon: pkt.lon,
+    symbolTable: pkt.symbol_table,
+    symbolCode: pkt.symbol_code,
+  });
+};
+
+// Update status display based on server decode availability
+function updateAprsStatus() {
+  if (typeof decodeConnected !== "undefined" && decodeConnected) {
+    if (!aprsActive) {
+      aprsStatus.textContent = "Server decode active";
+      aprsToggleBtn.textContent = "Start APRS (browser)";
+    }
+  }
+}
+setInterval(updateAprsStatus, 2000);
+
+// Auto-start APRS if it was running before page refresh (browser fallback)
 if (loadSetting("aprsRunning", false) && hasWebCodecs) {
   startAprs();
 }

src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/cw.js

@@ -457,3 +457,40 @@ cwToggleBtn.addEventListener("click", startCw);
 document.getElementById("cw-clear-btn").addEventListener("click", () => {
   cwOutputEl.innerHTML = "";
 });
+
+// --- Server-side CW decode handler ---
+let cwLastAppendTime = 0;
+window.onServerCw = function(evt) {
+  if (evt.text) {
+    // Append decoded text to output
+    const now = Date.now();
+    if (!cwOutputEl.lastElementChild || now - cwLastAppendTime > 10000 || evt.text === "\n") {
+      const line = document.createElement("div");
+      line.className = "cw-line";
+      cwOutputEl.appendChild(line);
+    }
+    cwLastAppendTime = now;
+    const lastLine = cwOutputEl.lastElementChild;
+    if (lastLine) {
+      lastLine.textContent += evt.text;
+    }
+    while (cwOutputEl.children.length > CW_MAX_LINES) {
+      cwOutputEl.removeChild(cwOutputEl.firstChild);
+    }
+    cwOutputEl.scrollTop = cwOutputEl.scrollHeight;
+  }
+  cwSignalIndicator.className = evt.signal_on ? "cw-signal-on" : "cw-signal-off";
+  cwWpmInput.value = evt.wpm;
+  cwToneInput.value = evt.tone_hz;
+};
+
+// Update status display based on server decode availability
+function updateCwStatus() {
+  if (typeof decodeConnected !== "undefined" && decodeConnected) {
+    if (!cwActive) {
+      cwStatusEl.textContent = "Server decode active";
+      cwToggleBtn.textContent = "Start CW (browser)";
+    }
+  }
+}
+setInterval(updateCwStatus, 2000);