SPL Meter 0.4.2: the device picker can build the tool it needs

NA could not list a single audio interface. The module was installed from
the catalog, which ships source only because the capture binary is
gitignored, and the picker shells out to that binary with --list. So it
returned nothing, forever:

  [spl-meter] device list failed: spawn .../spl-capture ENOENT

The missing-binary build existed, but only inside the listener, and the
listener only starts once a device has been picked. No tool meant no device
list, and no device meant no listener to build the tool. Nothing was going
to break that on its own.

The build now lives at module scope and both callers use it: init() asks for
it on mount whether or not a device is configured, and /devices asks again
each time it is called, so opening the admin page is enough to start it. It
is still a plain spawn that never touches the event loop, and health() now
names the situation instead of leaving an empty dropdown unexplained.

Also removed two per-listener build flags left shadowing the module-scope
ones, which would have made the "is a build already running" test always
false and let a second build start under the first.

Tested the way it actually failed: a data directory holding only the six
source files, no binary. The build starts on mount and /devices answers with
the real device list moments later.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

modules/spl-meter/client.js

@@ -17,6 +17,21 @@
 
 const FLOOR = -200;
 
+/**
+ * A dead input reads as a number, and a number on a wall is believed. Every
+ * tile therefore refuses to draw a level while the server says the input is
+ * digitally silent, and says why instead.
+ */
+function silentFor(payload) {
+  return payload && payload.silentSec ? payload.silentSec : 0;
+}
+
+function silentText(sec) {
+  if (sec < 90) return `No audio — ${sec} s`;
+  const m = Math.round(sec / 60);
+  return m < 90 ? `No audio — ${m} min` : `No audio — ${(m / 60).toFixed(1)} hours`;
+}
+
 /** Retention per frame for the RTA's smoothing setting. */
 const SMOOTHING = { off: 0, light: 0.45, medium: 0.72, heavy: 0.9 };
 
@@ -37,6 +52,9 @@ export default function create({ root, moduleApi }) {
       moduleApi.setStatus('error', payload.error);
     } else if (!payload.frame) {
       moduleApi.setStatus('connecting', 'waiting for the first reading');
+    } else if (silentFor(payload)) {
+      moduleApi.setStatus('error',
+        `No audio on the chosen input — digital silence for ${silentText(silentFor(payload)).replace('No audio — ', '')}`);
     } else if (!payload.calibrated) {
       moduleApi.setStatus('ok', 'Measuring, but uncalibrated — these are dBFS, not dB SPL');
     } else {
@@ -233,6 +251,16 @@ function readoutView(root, moduleApi) {
     render(payload) {
       const s = moduleApi.instanceSettings;
       const ch = pickChannel(payload, s);
+      const quiet = silentFor(payload);
+      if (quiet && ch) {
+        num.textContent = '––.–';
+        unit.textContent = '';
+        sub.hidden = false;
+        sub.textContent = silentText(quiet);
+        box.dataset.level = 'dead';
+        fit();
+        return;
+      }
       if (!payload || payload.error || !ch) {
         num.textContent = '––.–';
         sub.textContent = payload && payload.error ? payload.error : '';
@@ -286,6 +314,7 @@ function barsView(root, moduleApi) {
           </div>`).join('');
       }
       const s = moduleApi.instanceSettings;
+      const quiet = silentFor(payload);
       const warn = Number(s.warnAt), alarm = Number(s.alarmAt);
       const showPeak = s.peakHold !== false;
       const lo = payload.calibrated ? 40 : -80;
@@ -295,12 +324,12 @@ function barsView(root, moduleApi) {
         if (!el) continue;
         const value = readValue(c, { averaging: s.averaging });
         const pct = (v) => Math.max(0, Math.min(100, ((v - lo) / (hi - lo)) * 100));
-        el.querySelector('.spl-bar-fill').style.width = `${pct(value)}%`;
+        el.querySelector('.spl-bar-fill').style.width = quiet ? '0%' : `${pct(value)}%`;
         const peak = el.querySelector('.spl-bar-peak');
         peak.style.display = showPeak ? '' : 'none';
         if (showPeak) peak.style.left = `${pct(c.peakC)}%`;
-        el.querySelector('.spl-bar-value').textContent = fmt(value);
-        el.dataset.level = !payload.calibrated ? 'idle'
+        el.querySelector('.spl-bar-value').textContent = quiet ? '––.–' : fmt(value);
+        el.dataset.level = quiet ? 'dead' : !payload.calibrated ? 'idle'
           : value >= alarm ? 'alarm' : value >= warn ? 'warn' : 'ok';
         el.classList.toggle('clip', !!c.clip);
       }
@@ -321,7 +350,18 @@ function spectrumView(root, moduleApi, scrolling) {
   root.innerHTML = '<canvas class="spl-canvas"></canvas>';
   const canvas = root.querySelector('.spl-canvas');
   const ctx = canvas.getContext('2d', { alpha: false });
-  let painted = false;          // spectrogram: has the background been laid down
+  /**
+   * The spectrogram's scrolling history, on its own surface.
+   *
+   * It used to scroll by copying the visible canvas onto itself, which also
+   * copied whatever had been drawn on top of it — so every frame dragged the
+   * frequency labels and gridlines one step further along and left a smear.
+   * Only measured pixels belong on a surface that scrolls; annotations are
+   * drawn fresh over the top of it, every frame, and never into it.
+   */
+  let history = null;
+  let historyCtx = null;
+  let painted = false;          // spectrogram: has the history been cleared yet
   let smoothed = null;          // RTA: displayed values, damped toward the real ones
   let smoothedFor = '';
   let axisBtn = null;
@@ -389,10 +429,12 @@ function spectrumView(root, moduleApi, scrolling) {
       const muted = themeColor(root, '--muted', '#888');
       const border = themeColor(root, '--border', '#333');
 
-      if (!payload || !payload.frame || !payload.frame.bands) {
+      const quiet = silentFor(payload);
+      if (quiet || !payload || !payload.frame || !payload.frame.bands) {
         ctx.fillStyle = bg; ctx.fillRect(0, 0, w, h);
         ctx.fillStyle = muted; ctx.font = '12px system-ui'; ctx.textAlign = 'center';
-        ctx.fillText(payload?.error || 'Spectrum analysis is off', w / 2, h / 2);
+        ctx.fillText(quiet ? silentText(quiet)
+                     : (payload?.error || 'Spectrum analysis is off'), w / 2, h / 2);
         painted = false;
         return;
       }
@@ -466,62 +508,99 @@ function spectrumView(root, moduleApi, scrolling) {
       // ── spectrogram ──
       const timeX = axis() === 'x';
       const colW = 2;
-      const gutter = showLabels ? axisPad : 0;
-      // Frequency occupies whichever axis time does not.
-      const freqExtent = timeX ? h - gutter : w - gutter;
-      const timeExtent = timeX ? w : h;
+      // A label along the bottom needs only its line height; one down the
+      // side has to fit "12.5k" beside the plot rather than on top of it.
+      const gutter = (showLabels || grid) ? (timeX ? 30 : axisPad) : 0;
+      // Labels belong beside the frequency axis: down the left when frequency
+      // runs vertically, along the bottom when it runs horizontally.
+      const plotX = timeX ? gutter : 0;
+      const plotW = timeX ? w - gutter : w;
+      const plotH = timeX ? h : h - gutter;
+      const freqExtent = timeX ? plotH : plotW;
+      const timeExtent = timeX ? plotW : plotH;
+      if (plotW < 4 || plotH < 4) return;
 
-      if (!painted) { ctx.fillStyle = bg; ctx.fillRect(0, 0, w, h); painted = true; }
-
-      // Source rect in device pixels, destination in CSS pixels: the context
-      // carries a devicePixelRatio transform but the canvas as an image
-      // source does not, and letting drawImage infer them scales the picture
-      // up and pushes every column off the canvas.
-      if (timeX) {
-        ctx.drawImage(canvas, 0, 0, canvas.width, canvas.height, -colW, 0, w, h);
-      } else {
-        ctx.drawImage(canvas, 0, 0, canvas.width, canvas.height, 0, -colW, w, h);
+      // The history surface is sized to the plot, in device pixels, and is
+      // thrown away whenever that geometry changes — a scroll buffer means
+      // nothing once it is being stretched into a different shape.
+      const dpr = window.devicePixelRatio || 1;
+      const needW = Math.max(1, Math.round(plotW * dpr));
+      const needH = Math.max(1, Math.round(plotH * dpr));
+      if (!history || history.width !== needW || history.height !== needH) {
+        history = document.createElement('canvas');
+        history.width = needW;
+        history.height = needH;
+        historyCtx = history.getContext('2d', { alpha: false });
+        historyCtx.setTransform(dpr, 0, 0, dpr, 0, 0);
+        painted = false;
       }
+      if (!painted) {
+        historyCtx.fillStyle = bg;
+        historyCtx.fillRect(0, 0, plotW, plotH);
+        painted = true;
+      }
+
+      // Scroll the history, then add the newest column. The source rectangle
+      // is in device pixels and the destination in CSS pixels, because the
+      // context carries the dpr transform but the canvas as an image source
+      // does not.
+      historyCtx.drawImage(history, 0, 0, history.width, history.height,
+                           timeX ? -colW : 0, timeX ? 0 : -colW, plotW, plotH);
 
       const bandExtent = freqExtent / values.length;
       for (let i = 0; i < values.length; i++) {
-        ctx.fillStyle = heat(norm(values[i], payload.calibrated));
+        historyCtx.fillStyle = heat(norm(values[i], payload.calibrated));
         if (timeX) {
           // Low frequencies at the bottom, as every spectrogram has them.
-          ctx.fillRect(timeExtent - colW, freqExtent - (i + 1) * bandExtent,
-                       colW, Math.ceil(bandExtent) + 1);
+          historyCtx.fillRect(timeExtent - colW, freqExtent - (i + 1) * bandExtent,
+                              colW, Math.ceil(bandExtent) + 1);
         } else {
           // Low frequencies at the left.
-          ctx.fillRect(gutter + i * bandExtent, timeExtent - colW,
-                       Math.ceil(bandExtent) + 1, colW);
+          historyCtx.fillRect(i * bandExtent, timeExtent - colW,
+                              Math.ceil(bandExtent) + 1, colW);
         }
       }
 
-      if (grid || showLabels) {
-        const posOf = (f) => {
-          const t = Math.log2(f / freqs[0]) / Math.log2(freqs[freqs.length - 1] / freqs[0]);
-          return timeX ? freqExtent - t * freqExtent : gutter + t * freqExtent;
-        };
-        const labels = chooseLabels(freqs, posOf, timeX ? freqExtent : w, timeX ? 16 : 34);
-        ctx.fillStyle = bg;
-        if (timeX) ctx.fillRect(0, h - gutter, w, gutter);
-        else ctx.fillRect(0, 0, gutter, h);
-        ctx.fillStyle = muted; ctx.font = '9px system-ui';
-        ctx.strokeStyle = border; ctx.globalAlpha = grid ? 0.35 : 0; ctx.beginPath();
+      // Repaint the visible canvas from scratch every frame: history first,
+      // annotations over it. Nothing drawn here can ever reach the scroll.
+      ctx.fillStyle = bg; ctx.fillRect(0, 0, w, h);
+      ctx.drawImage(history, 0, 0, history.width, history.height,
+                    plotX, 0, plotW, plotH);
+
+      if (!grid && !showLabels) return;
+
+      const span = Math.log2(freqs[freqs.length - 1] / freqs[0]);
+      const posOf = (f) => {
+        const t = Math.log2(f / freqs[0]) / span;
+        return timeX ? plotH - t * plotH : plotX + t * plotW;
+      };
+      const labels = chooseLabels(freqs, posOf, timeX ? plotH : w, timeX ? 14 : 34);
+
+      if (grid) {
+        ctx.strokeStyle = border; ctx.lineWidth = 1; ctx.globalAlpha = 0.35;
+        ctx.beginPath();
         for (const l of labels) {
           if (timeX) {
             const y = Math.round(l.pos) + 0.5;
-            ctx.moveTo(0, y); ctx.lineTo(w, y);
+            ctx.moveTo(plotX, y); ctx.lineTo(w, y);
           } else {
             const x = Math.round(l.pos) + 0.5;
-            ctx.moveTo(x, 0); ctx.lineTo(x, h);
+            ctx.moveTo(x, 0); ctx.lineTo(x, plotH);
           }
         }
         ctx.stroke(); ctx.globalAlpha = 1;
-        ctx.textAlign = timeX ? 'left' : 'center';
-        for (const l of showLabels ? labels : []) {
-          if (timeX) ctx.fillText(hzLabel(l.f), 2, Math.min(h - gutter - 2, l.pos + 3));
-          else ctx.fillText(hzLabel(l.f), l.pos, h - 3);
+      }
+
+      if (showLabels) {
+        ctx.fillStyle = muted; ctx.font = '9px system-ui';
+        ctx.textAlign = timeX ? 'right' : 'center';
+        for (const l of labels) {
+          if (timeX) {
+            ctx.fillText(hzLabel(l.f), gutter - 2,
+                         Math.max(7, Math.min(h - 2, l.pos + 3)));
+          } else {
+            ctx.fillText(hzLabel(l.f), l.pos, h - 3);
+          }
         }
       }
     },

modules/spl-meter/module.json

@@ -1,7 +1,7 @@
 {
   "id": "spl-meter",
   "name": "SPL Meter",
-  "version": "0.3.1",
+  "version": "0.4.2",
   "proddash": ">=1.5.0",
   "description": "Calibrated sound level, Leq and RTA from an audio input on this machine",
   "permissions": [

modules/spl-meter/server.js

@@ -20,7 +20,7 @@
  */
 
 const path = require('path');
-const { createSplListener } = require('./spl-listener');
+const { createSplListener, ensureCaptureBinary } = require('./spl-listener');
 
 /** Reference level of a sound level calibrator. Effectively always 94 dB. */
 const CALIBRATOR_DB = 94;
@@ -30,6 +30,19 @@ const MEASURE_MS = 3000;
 /** SSE comment ping — keeps idle connections alive through sleepy Wi-Fi. */
 const PING_MS = 15000;
 
+/**
+ * Below this, unweighted, the input is not quiet — it is not there.
+ *
+ * A real input always carries something: a microphone in a silent room still
+ * reads about -83 dBFS, and even a muted converter dithers around -120. Only
+ * a stream of actual zeros reaches the capture tool's -200 floor, and that
+ * means the device handed us nothing at all.
+ */
+const SILENCE_DBFS = -150;
+/** How long that has to hold before saying so, so a gap between buffers or a
+    device changing sample rate mid-stream doesn't cry wolf. */
+const SILENCE_GRACE_MS = 5000;
+
 /** Set by init(), read by routes() — both are rebuilt together on re-init. */
 let state = null;
 
@@ -100,11 +113,20 @@ module.exports = {
       meta: null,
       error: '',
       streams: new Set(),
+      silentSince: null,
+      toolMissing: '',
       listener: null,
       lastSent: '',
       pinger: null,
     };
 
+    // Before anything else: the device picker shells out to this tool, so a
+    // machine that installed the module from the catalog (source only — the
+    // binary is gitignored) needs the build kicked off here. Waiting for a
+    // listener would never happen: no tool means no device list, and no
+    // device means no listener.
+    state.toolMissing = ensureCaptureBinary({ moduleDir, log });
+
     if (!config.enabled) {
       state.error = 'Sound level measurement is off — turn it on in ProdDash settings';
       return { stop() { teardown(); }, health: () => ({ status: 'error', message: state.error }) };
@@ -143,6 +165,12 @@ module.exports = {
         state.error = '';
         state.frame = update.frame;
         state.meta = update.meta;
+        // Digital silence on every channel is a dead input, not a reading.
+        // Saying "ok" through this is what made a stopped Dante device look
+        // like a frozen module for a day and a half.
+        const dead = update.frame.ch.every(
+          (c) => !Number.isFinite(c.dbfs) || c.dbfs <= SILENCE_DBFS);
+        state.silentSince = dead ? (state.silentSince || Date.now()) : null;
         broadcast();
       },
     });
@@ -157,8 +185,16 @@ module.exports = {
     return {
       stop() { teardown(); },
       health() {
+        if (state.toolMissing && !fsExists(path.join(moduleDir, 'spl-capture'))) {
+          return { status: 'error', message: state.toolMissing };
+        }
         if (state.error) return { status: 'error', message: state.error };
         if (!state.frame) return { status: 'connecting', message: 'waiting for the first reading' };
+        const quiet = silentMs();
+        if (quiet > SILENCE_GRACE_MS) {
+          return { status: 'error',
+                   message: `No audio from ${config.device} — digital silence for ${describe(quiet)}` };
+        }
         const n = state.channels.length;
         const what = `${n} channel${n === 1 ? '' : 's'} on ${config.device}`;
         return state.calibrated
@@ -275,6 +311,13 @@ module.exports = {
       /** Device list for the admin page. Runs the capture tool's --list,
           which is the only thing that knows what CoreAudio can see. */
       'GET /devices': async (req, res) => {
+        const missing = ensureCaptureBinary({ moduleDir: __dirname, log });
+        if (missing) {
+          if (state) state.toolMissing = missing;
+          log(`device list unavailable — ${missing}`);
+          json(res, 200, { options: [] });
+          return;
+        }
         try {
           const devices = await listDevices();
           json(res, 200, {
@@ -351,10 +394,26 @@ module.exports = {
 
 /* ── helpers ────────────────────────────────────────────────────────── */
 
+/** How long every channel has been at digital silence, in ms. */
+function silentMs() {
+  return state && state.silentSince ? Date.now() - state.silentSince : 0;
+}
+
+function describe(ms) {
+  const s = Math.round(ms / 1000);
+  if (s < 90) return `${s} s`;
+  const m = Math.round(s / 60);
+  return m < 90 ? `${m} min` : `${(m / 60).toFixed(1)} hours`;
+}
+
 function snapshot() {
-  if (!state) return { error: 'not measuring', calibrated: false, channels: [], frame: null };
+  if (!state) return { error: 'not measuring', calibrated: false, channels: [], frame: null, silentSec: 0 };
+  // Seconds, not milliseconds: this goes on the wire 20×/s and a value that
+  // changed every frame would make the fan-out's change check useless.
+  const quiet = silentMs();
   return {
     error: state.error,
+    silentSec: quiet > SILENCE_GRACE_MS ? Math.round(quiet / 1000) : 0,
     calibrated: state.calibrated,
     channels: state.channels,
     weighting: state.meta ? state.meta.weighting : '',
@@ -397,6 +456,10 @@ function listDevices() {
   });
 }
 
+function fsExists(p) {
+  try { return require('fs').existsSync(p); } catch { return false; }
+}
+
 function json(res, code, body) {
   const text = JSON.stringify(body);
   res.writeHead(code, {

modules/spl-meter/spl-listener.js

@@ -17,7 +17,8 @@
  * module's ltc-capture. It normally arrives already built — compiled beside
  * the app, or copied from any Mac of the same architecture. When it is
  * missing this will build it, but in the background and never on the event
- * loop: see ensureBinary for what that cost the first time it was wrong.
+ * loop, and from module scope so the device picker can trigger it too — see
+ * ensureCaptureBinary for what both of those cost the first time round.
  *
  * The same macOS gotcha applies as for LTC, and is worth repeating because
  * it costs an afternoon every time: a ProdDash launched over SSH or from a
@@ -30,6 +31,74 @@ const path = require('path');
 const fs = require('fs');
 const { spawn } = require('child_process');
 
+const BUILD_HELP = 'Sound level capture tool missing — build it on any Apple Silicon Mac with '
+  + '`swiftc -O -o modules/spl-meter/spl-capture modules/spl-meter/spl-capture.swift` '
+  + 'and copy it next to spl-capture.swift';
+const BUILDING = 'Building the capture tool — this takes a minute or two';
+
+/**
+ * Build the capture tool if it is missing, WITHOUT blocking, and shared by
+ * everything that needs it.
+ *
+ * This lives at module scope rather than inside a listener because of a trap
+ * the first version walked into: the admin page's device picker runs the tool
+ * with --list, but the build only ran when a listener started, and a listener
+ * only starts once a device has been picked. On a machine that got the module
+ * from the catalog — source only, the binary being gitignored — the picker
+ * was empty, and nothing would ever fill it.
+ *
+ * It also must never block. It was a spawnSync once, copied from the LTC
+ * listener where the source is a third the size and builds in seconds. Here
+ * it took nearly two minutes on the production Mac and held the Node event
+ * loop for all of it, freezing every other module, then did it again on the
+ * next retry.
+ *
+ * The binary should normally already be there: built beside the app, or
+ * copied from any Mac of the same architecture. This is the fallback.
+ *
+ * @returns {string} '' when the tool is ready, otherwise what to say.
+ */
+let building = false;
+let buildFailed = false;
+
+function ensureCaptureBinary({ moduleDir, log, onReady }) {
+  const bin = path.join(moduleDir, 'spl-capture');
+  if (fs.existsSync(bin)) return '';
+  const src = bin + '.swift';
+  if (!fs.existsSync(src)) return 'spl-capture.swift is missing from the module folder';
+  if (building) return BUILDING;
+  if (buildFailed) return BUILD_HELP;
+
+  building = true;
+  log('spl-capture binary missing — building it in the background');
+  const build = spawn('swiftc', ['-O', '-o', bin, src], { stdio: ['ignore', 'ignore', 'pipe'] });
+  let buildErr = '';
+  build.stderr.setEncoding('utf8');
+  build.stderr.on('data', (t) => { buildErr = (buildErr + t).slice(-800); });
+  const giveUp = setTimeout(() => {
+    try { build.kill('SIGKILL'); } catch { /* already gone */ }
+  }, 300000);
+  build.on('error', (err) => {
+    clearTimeout(giveUp);
+    building = false; buildFailed = true;
+    log(`swiftc could not be run: ${err.message}`);
+  });
+  build.on('exit', (code) => {
+    clearTimeout(giveUp);
+    building = false;
+    if (code === 0 && fs.existsSync(bin)) {
+      log('spl-capture built');
+      buildFailed = false;
+      if (typeof onReady === 'function') onReady();
+      return;
+    }
+    buildFailed = true;
+    log(`spl-capture build failed (exit ${code})`
+      + (buildErr ? `: ${buildErr.trim().split('\n').pop()}` : ''));
+  });
+  return BUILDING;
+}
+
 const RESTART_MS = 5000;
 /** An immediate exit is config-shaped (bad device, channel out of range) —
     retrying every 5 s would only fill the log with the same sentence. */
@@ -53,64 +122,13 @@ function createSplListener(opts) {
   let stallTimer = null;
   let startedAt = 0;
   let meta = null;
-  let building = false;
-  let buildFailed = false;
   let lastFrameWall = 0;
 
-  const BUILD_HELP = 'Sound level capture tool missing — build it on any Apple Silicon Mac with '
-    + '`swiftc -O -o modules/spl-meter/spl-capture modules/spl-meter/spl-capture.swift` '
-    + 'and copy it next to spl-capture.swift';
-
-  /**
-   * Build the capture tool if it is missing, WITHOUT blocking.
-   *
-   * This used to be a spawnSync, copied from the LTC listener where the
-   * source is a third the size and builds in a few seconds. Here it took
-   * nearly two minutes on the production Mac and froze the entire ProdDash
-   * server for every second of it — one module's optional helper took the
-   * whole dashboard down, then did it again on every retry. Nothing that
-   * runs while a service might be on is allowed to hold the event loop.
-   *
-   * The build is a fallback for a module installed from the catalog on a
-   * machine with a Swift toolchain. The normal path is a binary built
-   * alongside the app, or copied from any same-architecture Mac.
-   *
-   * @returns {string} '' when the binary is ready, otherwise what to say.
-   */
+  /** '' when the tool is ready, otherwise what to say about it. */
   function ensureBinary() {
-    if (fs.existsSync(bin)) return '';
-    const src = bin + '.swift';
-    if (!fs.existsSync(src)) return 'spl-capture.swift is missing from the module folder';
-    if (building) return 'Building the capture tool — this takes a minute or two';
-    if (buildFailed) return BUILD_HELP;
-
-    building = true;
-    log('spl-capture binary missing — building it in the background');
-    const build = spawn('swiftc', ['-O', '-o', bin, src], { stdio: ['ignore', 'ignore', 'pipe'] });
-    let buildErr = '';
-    build.stderr.setEncoding('utf8');
-    build.stderr.on('data', (t) => { buildErr = (buildErr + t).slice(-800); });
-    const giveUp = setTimeout(() => {
-      try { build.kill('SIGKILL'); } catch { /* already gone */ }
-    }, 300000);
-    build.on('error', (err) => {
-      clearTimeout(giveUp);
-      building = false; buildFailed = true;
-      log(`swiftc could not be run: ${err.message}`);
-    });
-    build.on('exit', (code) => {
-      clearTimeout(giveUp);
-      building = false;
-      if (code === 0 && fs.existsSync(bin)) {
-        log('spl-capture built');
-        buildFailed = false;
-        if (!stopped) { clearTimeout(restartTimer); restartTimer = null; start(); }
-        return;
-      }
-      buildFailed = true;
-      log(`spl-capture build failed (exit ${code})` + (buildErr ? `: ${buildErr.trim().split('\n').pop()}` : ''));
-    });
-    return 'Building the capture tool — this takes a minute or two';
+    return ensureCaptureBinary({ moduleDir, log, onReady() {
+      if (!stopped) { clearTimeout(restartTimer); restartTimer = null; start(); }
+    } });
   }
 
   function scheduleRestart(ms) {
@@ -137,7 +155,7 @@ function createSplListener(opts) {
       onUpdate({ error: missing });
       // A build in flight calls start() itself when it lands; anything else
       // is config-shaped and should back off hard rather than spin.
-      if (!building) scheduleRestart(BAD_CONFIG_RETRY_MS);
+      if (missing !== BUILDING) scheduleRestart(BAD_CONFIG_RETRY_MS);
       return;
     }
 
@@ -236,4 +254,4 @@ function createSplListener(opts) {
   };
 }
 
-module.exports = { createSplListener };
+module.exports = { createSplListener, ensureCaptureBinary };

modules/spl-meter/style.css

@@ -57,6 +57,11 @@
 [data-module="spl-meter"] .spl-readout[data-level="alarm"] .spl-num { color: var(--danger); }
 [data-module="spl-meter"] .spl-readout[data-level="idle"] .spl-num { color: var(--muted); }
 
+/* A dead input reads danger, not muted: silence that is a fault should not
+   look like silence that is a quiet room. */
+[data-module="spl-meter"] .spl-readout[data-level="dead"] .spl-num { color: var(--danger); }
+[data-module="spl-meter"] .spl-readout[data-level="dead"] .spl-sub { color: var(--danger); }
+
 /* ── level bars ───────────────────────────────────────────────────── */
 
 [data-module="spl-meter"] .spl-bars {
@@ -100,6 +105,7 @@
 [data-module="spl-meter"] .spl-bar[data-level="warn"] .spl-bar-fill { background: var(--warn); }
 [data-module="spl-meter"] .spl-bar[data-level="alarm"] .spl-bar-fill { background: var(--danger); }
 [data-module="spl-meter"] .spl-bar[data-level="idle"] .spl-bar-fill { background: var(--muted); }
+[data-module="spl-meter"] .spl-bar[data-level="dead"] .spl-bar-value { color: var(--danger); }
 
 /* Peak hold sits on the track rather than inside the fill, so it stays
    visible when the bar falls away underneath it. */