fix: waterfall monitor audio delay and unresponsive stop button

- _waitForPlayback now only succeeds on playing/timeupdate events, not
  loadeddata/canplay which fire from just the WAV header before real
  audio arrives
- stopMonitor() pauses audio and updates UI immediately instead of
  blocking on the backend stop request (1+ second delay)
- Reduced backend audio stop sleep from 1.0s to 0.15s; the start
  retry loop already handles USB contention

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,8 @@ All notable changes to iNTERCEPT will be documented in this file.
 ### Fixed
 - Waterfall control panel rendered as unstyled text for up to 20 seconds on first visit — CSS is now loaded eagerly with the rest of the page assets
 - WebSDR globe failed to render on first page load — initialization now waits for a layout frame before mounting the WebGL renderer, ensuring the container has non-zero dimensions
+- Waterfall monitor audio took minutes to start — `_waitForPlayback` now only reports success on actual audio playback (`playing`/`timeupdate`), not from the WAV header alone (`loadeddata`/`canplay`)
+- Waterfall monitor could not be stopped — `stopMonitor()` now pauses audio and updates the UI immediately instead of waiting for the backend stop request (which blocked for 1+ seconds during SDR process cleanup)
 
 ---
 

config.py

@@ -17,6 +17,8 @@ CHANGELOG = [
         "highlights": [
             "Waterfall control panel no longer shows as unstyled text on first visit",
             "WebSDR globe renders correctly on first page load without requiring a refresh",
+            "Waterfall monitor audio no longer takes minutes to start — playback detection now waits for real audio data instead of just the WAV header",
+            "Waterfall monitor stop is now instant — audio pauses and UI updates immediately instead of waiting for backend cleanup",
         ]
     },
     {

static/js/modes/waterfall.js

@@ -900,19 +900,27 @@ const Waterfall = (function () {
                 resolve(ok);
             };
 
-            const onReady = () => finish(true);
+            // Only treat actual playback as success.  `loadeddata` and
+            // `canplay` fire when just the WAV header arrives — before any
+            // real audio samples have been decoded — which caused the
+            // monitor to report "started" while the stream was still silent.
+            const onReady = () => {
+                if (player.currentTime > 0 || (!player.paused && player.readyState >= 4)) {
+                    finish(true);
+                }
+            };
             const onFail = () => finish(false);
-            const events = ['playing', 'timeupdate', 'canplay', 'loadeddata'];
+            const events = ['playing', 'timeupdate'];
             const failEvents = ['error', 'abort', 'stalled', 'ended'];
 
             events.forEach((evt) => player.addEventListener(evt, onReady));
             failEvents.forEach((evt) => player.addEventListener(evt, onFail));
 
             timer = setTimeout(() => {
-                finish(!player.paused && (player.currentTime > 0 || player.readyState >= 2));
+                finish(!player.paused && player.currentTime > 0);
             }, timeoutMs);
 
-            if (!player.paused && (player.currentTime > 0 || player.readyState >= 2)) {
+            if (!player.paused && player.currentTime > 0) {
                 finish(true);
             }
         });
@@ -2571,6 +2579,7 @@ const Waterfall = (function () {
             }
 
             if (attempt < maxAttempts) {
+                _setMonitorState(`Waiting for audio stream (attempt ${attempt}/${maxAttempts})...`);
                 await _wait(220 * attempt);
                 continue;
             }
@@ -2813,12 +2822,9 @@ const Waterfall = (function () {
         clearTimeout(_monitorRetuneTimer);
         _audioConnectNonce += 1;
 
-        try {
+        // Immediately pause audio and update the UI so the user gets instant
-            await fetch('/receiver/audio/stop', { method: 'POST' });
+        // feedback.  The backend cleanup (which can block for 1-2 s while the
-        } catch (_) {
+        // SDR process group is reaped) happens afterwards.
-            // Ignore backend stop errors
-        }
-
         _stopSmeter();
         _setUnlockVisible(false);
         _audioUnlockRequired = false;
@@ -2836,6 +2842,13 @@ const Waterfall = (function () {
             _setVisualStatus('READY');
         }
 
+        // Backend stop is fire-and-forget; UI is already updated above.
+        try {
+            await fetch('/receiver/audio/stop', { method: 'POST' });
+        } catch (_) {
+            // Ignore backend stop errors
+        }
+
         if (resumeWaterfall && _active) {
             _resumeWaterfallAfterMonitor = false;
             await start();

templates/index.html

@@ -2936,7 +2936,7 @@
     <script src="{{ url_for('static', filename='js/core/voice-alerts.js') }}?v={{ version }}&r=voicefix2"></script>
     <script src="{{ url_for('static', filename='js/core/keyboard-shortcuts.js') }}"></script>
     <script src="{{ url_for('static', filename='js/core/cheat-sheets.js') }}"></script>
-    <script src="{{ url_for('static', filename='js/modes/waterfall.js') }}?v={{ version }}&r=wfdeck20"></script>
+    <script src="{{ url_for('static', filename='js/modes/waterfall.js') }}?v={{ version }}&r=wfdeck21"></script>
 
     <script>
         // ============================================