[feat](trx-frontend-http): add LNA gain control UI and API

Add POST /set_sdr_lna_gain endpoint. Add an LNA Gain input+Set button
to the SDR settings row, styled identically to RF Gain. The control is
hidden until the server reports a sdr_lna_gain_db value (i.e. devices
that expose an LNA gain element). AGC disables it alongside RF Gain.

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

@@ -2719,6 +2719,11 @@ function render(update) {
     ) {
       sdrGainEl.value = String(Math.round(update.filter.sdr_gain_db));
     }
+    if (sdrLnaGainEl && typeof update.filter.sdr_lna_gain_db === "number"
+      && document.activeElement !== sdrLnaGainEl) {
+      sdrLnaGainEl.value = String(Math.round(update.filter.sdr_lna_gain_db));
+      if (sdrLnaGainControlsEl) sdrLnaGainControlsEl.style.display = "";
+    }
     if (wfmDeemphasisEl && typeof update.filter.wfm_deemphasis_us === "number") {
       wfmDeemphasisEl.value = String(update.filter.wfm_deemphasis_us);
     }
@@ -6720,6 +6725,9 @@ const sdrSettingsRowEl = document.getElementById("sdr-settings-row");
 const sdrGainControlsEl = document.getElementById("sdr-gain-controls");
 const sdrGainEl = document.getElementById("sdr-gain-db");
 const sdrGainSetBtn = document.getElementById("sdr-gain-set");
+const sdrLnaGainControlsEl = document.getElementById("sdr-lna-gain-controls");
+const sdrLnaGainEl = document.getElementById("sdr-lna-gain-db");
+const sdrLnaGainSetBtn = document.getElementById("sdr-lna-gain-set");
 const sdrAgcEl = document.getElementById("sdr-agc-enabled");
 const wfmStFlagEl = document.getElementById("wfm-st-flag");
 const sdrSquelchWrapEl = document.getElementById("sdr-squelch-wrap");
@@ -6896,10 +6904,12 @@ function submitSdrGain() {
   postPath(`/set_sdr_gain?db=${encodeURIComponent(parsed)}`).catch(() => {});
 }
 function updateSdrGainInputState() {
-  if (!sdrAgcEl || !sdrGainEl || !sdrGainSetBtn) return;
+  if (!sdrAgcEl) return;
   const agcOn = sdrAgcEl.checked;
-  sdrGainEl.disabled = agcOn;
+  if (sdrGainEl) sdrGainEl.disabled = agcOn;
-  sdrGainSetBtn.disabled = agcOn;
+  if (sdrGainSetBtn) sdrGainSetBtn.disabled = agcOn;
+  if (sdrLnaGainEl) sdrLnaGainEl.disabled = agcOn;
+  if (sdrLnaGainSetBtn) sdrLnaGainSetBtn.disabled = agcOn;
 }
 if (sdrAgcEl) {
   sdrAgcEl.addEventListener("change", () => {
@@ -6918,6 +6928,23 @@ if (sdrGainEl) {
     }
   });
 }
+function submitSdrLnaGain() {
+  if (!sdrLnaGainEl) return;
+  const parsed = Number.parseFloat(sdrLnaGainEl.value);
+  if (!Number.isFinite(parsed) || parsed < 0) return;
+  postPath(`/set_sdr_lna_gain?db=${encodeURIComponent(parsed)}`).catch(() => {});
+}
+if (sdrLnaGainSetBtn) {
+  sdrLnaGainSetBtn.addEventListener("click", submitSdrLnaGain);
+}
+if (sdrLnaGainEl) {
+  sdrLnaGainEl.addEventListener("keydown", (ev) => {
+    if (ev.key === "Enter") {
+      ev.preventDefault();
+      submitSdrLnaGain();
+    }
+  });
+}
 function updateWfmControls() {
   if (!wfmControlsCol) return;
   const mode = (modeEl && modeEl.value ? modeEl.value : "").toUpperCase();

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

@@ -268,6 +268,13 @@
                   </label>
                   <button id="sdr-gain-set" type="button" class="wfm-inline-btn">Set</button>
                 </div>
+                <div class="wfm-gain-group" id="sdr-lna-gain-controls">
+                  <label class="wfm-control">
+                    <span class="wfm-control-label">LNA Gain</span>
+                    <input id="sdr-lna-gain-db" class="status-input" type="number" min="0" max="60" step="1" inputmode="decimal">
+                  </label>
+                  <button id="sdr-lna-gain-set" type="button" class="wfm-inline-btn">Set</button>
+                </div>
               </div>
             </div>
             <div class="full-row label-below-row" id="vchan-row">

src/trx-client/trx-frontend/trx-frontend-http/src/api.rs

@@ -873,6 +873,19 @@ pub async fn set_sdr_gain(
     send_command(&rig_tx, RigCommand::SetSdrGain(query.db)).await
 }
 
+#[derive(serde::Deserialize)]
+pub struct SdrLnaGainQuery {
+    pub db: f64,
+}
+
+#[post("/set_sdr_lna_gain")]
+pub async fn set_sdr_lna_gain(
+    query: web::Query<SdrLnaGainQuery>,
+    rig_tx: web::Data<mpsc::Sender<RigRequest>>,
+) -> Result<HttpResponse, Error> {
+    send_command(&rig_tx, RigCommand::SetSdrLnaGain(query.db)).await
+}
+
 #[derive(serde::Deserialize)]
 pub struct SdrAgcQuery {
     pub enabled: bool,
@@ -1546,6 +1559,7 @@ pub fn configure(cfg: &mut web::ServiceConfig) {
         .service(set_bandwidth)
         .service(set_fir_taps)
         .service(set_sdr_gain)
+        .service(set_sdr_lna_gain)
         .service(set_sdr_agc)
         .service(set_sdr_squelch)
         .service(set_wfm_deemphasis)