[feat](trx-frontend-http): add connection-lost overlay for trx-client and trx-server failures

Show a full-screen blurred overlay (reusing decode-history-overlay styles)
when the SSE connection to trx-client drops or when trx-server is reported
unreachable via server_connected=false.  The overlay distinguishes the two
failure modes with separate titles and sub-text.  It is dismissed on
es.onopen (trx-client back) or when a message with server_connected!=false
arrives (trx-server back), and cleared on explicit disconnect/logout.

Co-authored-by: Claude Sonnet 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

@@ -334,6 +334,9 @@ const loadingSub = document.getElementById("loading-sub");
 const decodeHistoryOverlayEl = document.getElementById("decode-history-overlay");
 const decodeHistoryOverlayTitleEl = document.getElementById("decode-history-overlay-title");
 const decodeHistoryOverlaySubEl = document.getElementById("decode-history-overlay-sub");
+const connLostOverlayEl = document.getElementById("conn-lost-overlay");
+const connLostOverlayTitleEl = document.getElementById("conn-lost-overlay-title");
+const connLostOverlaySubEl = document.getElementById("conn-lost-overlay-sub");
 const overviewCanvas = document.getElementById("overview-canvas");
 const signalOverlayCanvas = document.getElementById("signal-overlay-canvas");
 const overviewGl = typeof createTrxWebGlRenderer === "function"
@@ -401,6 +404,13 @@ function setDecodeHistoryOverlayVisible(visible, title = "", sub = "") {
   if (decodeHistoryOverlaySubEl) decodeHistoryOverlaySubEl.textContent = sub || "";
   decodeHistoryOverlayEl.classList.toggle("is-hidden", !visible);
 }
+
+function setConnLostOverlay(visible, title = "Connection lost", sub = "Retrying\u2026") {
+  if (!connLostOverlayEl) return;
+  if (connLostOverlayTitleEl) connLostOverlayTitleEl.textContent = title;
+  if (connLostOverlaySubEl) connLostOverlaySubEl.textContent = sub;
+  connLostOverlayEl.classList.toggle("is-hidden", !visible);
+}
 const decodeHistoryTextDecoder = typeof TextDecoder === "function" ? new TextDecoder() : null;
 let decodeHistoryReplayActive = false;
 let decodeMapSyncPending = false;
@@ -3093,6 +3103,7 @@ function connect() {
   es = new EventSource("/events");
   lastEventAt = Date.now();
   es.onopen = () => {
+    setConnLostOverlay(false);
     pollFreshSnapshot();
     refreshRigList();
   };
@@ -3105,8 +3116,10 @@ function connect() {
       lastEventAt = Date.now();
       if (data.server_connected === false) {
         powerHint.textContent = "trx-server connection lost";
-      } else if (data.initialized) {
+        setConnLostOverlay(true, "trx-server connection lost", "trx-client is running but cannot reach the radio server");
-        powerHint.textContent = readyText();
+      } else {
+        setConnLostOverlay(false);
+        if (data.initialized) powerHint.textContent = readyText();
       }
     } catch (e) {
       console.error("Bad event data", e);
@@ -3125,6 +3138,7 @@ function connect() {
     // Check if this is an auth error by looking at readyState
     if (es.readyState === EventSource.CLOSED) {
       powerHint.textContent = "trx-client connection lost, retrying\u2026";
+      setConnLostOverlay(true, "trx-client connection lost", "Retrying\u2026");
       es.close();
       pollFreshSnapshot();
       scheduleReconnect(1000);
@@ -3135,6 +3149,7 @@ function connect() {
     const now = Date.now();
     if (now - lastEventAt > 15000) {
       powerHint.textContent = "trx-client connection lost, retrying\u2026";
+      setConnLostOverlay(true, "trx-client connection lost", "Retrying\u2026");
       es.close();
       pollFreshSnapshot();
       scheduleReconnect(250);
@@ -3163,6 +3178,7 @@ function disconnect() {
     reconnectTimer = null;
   }
   setDecodeHistoryOverlayVisible(false);
+  setConnLostOverlay(false);
 }
 
 // Yield the main thread so the browser can paint before heavy async work.

src/trx-client/trx-frontend/trx-frontend-http/assets/web/index.html

@@ -980,6 +980,12 @@
       <div id="decode-history-overlay-sub" class="decode-history-overlay-sub">Preparing recent decodes for the UI</div>
     </div>
   </div>
+  <div id="conn-lost-overlay" class="decode-history-overlay is-hidden" aria-live="assertive" aria-atomic="true">
+    <div class="decode-history-overlay-card">
+      <div id="conn-lost-overlay-title" class="decode-history-overlay-title">Connection lost</div>
+      <div id="conn-lost-overlay-sub" class="decode-history-overlay-sub">Retrying…</div>
+    </div>
+  </div>
   <script src="/webgl-renderer.js"></script>
   <script src="/app.js"></script>
   <script src="/ais.js"></script>