[feat](trx-frontend-http): add frequency layers display for virtual channels

Render virtual channels as absolutely-positioned layer strips inside a
shared relative container (#vchan-freq-layers). Layers are sorted by
frequency ascending so higher-frequency channels receive a higher z-index
and sit on top by default. Hovering any layer temporarily assigns it the
maximum z-index to bring it to the front; leaving restores the original
stacking order. Each layer is offset by 11 px vertically so all channels
remain visible as a staggered card stack.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

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

@@ -262,6 +262,7 @@
             <div class="full-row label-below-row" id="vchan-row" style="display:none;">
               <div class="label"><span>Channels</span></div>
               <div class="vchan-picker" id="vchan-picker"></div>
+              <div class="vchan-freq-layers" id="vchan-freq-layers"></div>
             </div>
             <div class="full-row label-below-row">
               <div class="label"><span>Signal</span></div>

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

@@ -49,6 +49,50 @@ function vchanHandleChannels(data) {
   }
 }
 
+function vchanRenderLayers() {
+  const container = document.getElementById("vchan-freq-layers");
+  if (!container) return;
+  container.innerHTML = "";
+
+  if (vchanChannels.length === 0) {
+    container.style.height = "0";
+    return;
+  }
+
+  // Sort by frequency ascending so higher-frequency channels get higher z-index.
+  const sorted = [...vchanChannels].sort((a, b) => a.freq_hz - b.freq_hz);
+
+  const LAYER_H_PX = 32;
+  const STEP_PX = 11; // vertical offset between layers so each peeks below the next
+  const totalH = LAYER_H_PX + (sorted.length - 1) * STEP_PX;
+  container.style.height = totalH + "px";
+
+  sorted.forEach((ch, i) => {
+    const layer = document.createElement("div");
+    layer.className = "vchan-freq-layer";
+    if (ch.id === vchanActiveId) layer.classList.add("active");
+
+    layer.style.top = (i * STEP_PX) + "px";
+    // Higher frequency → higher index → higher z-index (sits on top by default).
+    const defaultZ = i + 1;
+    layer.style.zIndex = defaultZ;
+
+    layer.textContent = `${ch.index}: ${vchanFmtFreq(ch.freq_hz)} ${ch.mode}`;
+    layer.title = `Ch ${ch.index}: ${vchanFmtFreq(ch.freq_hz)} ${ch.mode} · ${ch.subscribers} subscriber${ch.subscribers !== 1 ? "s" : ""}`;
+
+    // Bring hovered layer to the front; restore on leave.
+    const maxZ = sorted.length + 10;
+    layer.addEventListener("mouseenter", () => { layer.style.zIndex = maxZ; });
+    layer.addEventListener("mouseleave", () => { layer.style.zIndex = defaultZ; });
+
+    layer.addEventListener("click", () => {
+      if (ch.id !== vchanActiveId) vchanSubscribe(ch.id);
+    });
+
+    container.appendChild(layer);
+  });
+}
+
 function vchanRender() {
   const picker = document.getElementById("vchan-picker");
   if (!picker) return;
@@ -93,6 +137,7 @@ function vchanRender() {
   addBtn.addEventListener("click", vchanAllocate);
   picker.appendChild(addBtn);
 
+  vchanRenderLayers();
   vchanSyncAccentUI();
 }
 

src/trx-client/trx-frontend/trx-frontend-http/assets/web/style.css

@@ -392,6 +392,44 @@ input.status-input, select.status-input { width: 100%; padding: 0.45rem 0.5rem;
   border-color: var(--vchan-color);
   box-shadow: inset 3px 0 0 var(--vchan-color);
 }
+/* Frequency layers: absolutely-positioned channel strips stacked by frequency */
+.vchan-freq-layers {
+  position: relative;
+  margin-top: 0.5rem;
+  /* height is set dynamically by vchanRenderLayers() */
+}
+.vchan-freq-layer {
+  position: absolute;
+  left: 0;
+  right: 0;
+  height: 2rem;
+  display: flex;
+  align-items: center;
+  padding: 0 0.6rem;
+  border-radius: 6px;
+  background: var(--input-bg);
+  border: 1px solid var(--border-light);
+  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
+  font-size: 0.82rem;
+  color: var(--text-muted);
+  cursor: pointer;
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  transition: border-color 0.12s, box-shadow 0.12s;
+}
+.vchan-freq-layer:hover {
+  border-color: var(--vchan-color);
+  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.35);
+  color: var(--text);
+}
+.vchan-freq-layer.active {
+  background: var(--btn-bg);
+  color: var(--text);
+  font-weight: 600;
+  border-color: var(--vchan-color);
+  box-shadow: inset 3px 0 0 var(--vchan-color);
+}
 /* Applied to #freq and #spectrum-bw-input when on a virtual channel */
 .vchan-ch-active {
   border-color: var(--vchan-color) !important;