Close try/catch gap around appsink pull_sample()

Standalone gst-launch testing confirmed appsink-as-playbin-video-sink
works fine outside the extension (reaches PLAYING, negotiates caps,
runs to completion), narrowing the "no frames received" symptom down
to something inside our own new-sample handling in the shell process.

_onNewSample()'s try/catch didn't cover the sink.pull_sample() call
itself — if that specific call throws when invoked as a GJS signal
callback, the exception bypassed our logging entirely, falling back
to GJS's generic uncaught-exception path (which, like the
openPreferences case, may not mention "benthicbloom" and gets missed
by a filtered grep). Now the whole handler is covered, logs when the
signal fires for the first time, logs a null pull_sample() or failed
buffer.map() explicitly, and the watchdog reports the new-sample fire
count so we can tell "signal never fired" from "signal fired but
processing failed" on the next test.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019RDqbdjsiisSU7CbQke4g8

lib/liveWallpaper.js

@@ -50,6 +50,7 @@ export class LiveWallpaperManager {
         this._upowerSignalId = 0;
 
         this._frameCount = 0;
+        this._newSampleCallCount = 0;
         this._noFrameWatchdogId = 0;
     }
 
@@ -162,13 +163,16 @@ export class LiveWallpaperManager {
             this._logger.debug(`playbin.set_state(PLAYING) returned ${stateChangeResult}`);
 
             this._frameCount = 0;
+            this._newSampleCallCount = 0;
             this._noFrameWatchdogId = GLib.timeout_add_seconds(GLib.PRIORITY_DEFAULT, 4, () => {
                 this._noFrameWatchdogId = 0;
                 if (this._active && this._frameCount === 0) {
                     this._logger.warn(
-                        'Live wallpaper: no frames received 4s after starting playback. ' +
+                        `Live wallpaper: no frames received 4s after starting playback ` +
-                        'The pipeline likely stalled during caps negotiation or preroll without ' +
+                        `(new-sample signal fired ${this._newSampleCallCount} times). ` +
-                        'raising an error — check for GStreamer WARNING messages logged above.');
+                        'If that count is 0, the signal itself never fired (check for a stalled ' +
+                        'pipeline above); if it is nonzero, pull_sample()/buffer processing is failing ' +
+                        '— check for a "Failed to process live wallpaper frame" error above.');
                 }
                 return GLib.SOURCE_REMOVE;
             });
@@ -185,19 +189,27 @@ export class LiveWallpaperManager {
 
     _onNewSample(sink) {
         const Gst = this._Gst;
-        const sample = sink.pull_sample();
+        this._newSampleCallCount = (this._newSampleCallCount ?? 0) + 1;
-        if (!sample)
+        if (this._newSampleCallCount === 1)
-            return Gst.FlowReturn.OK;
+            this._logger.debug('Live wallpaper: new-sample signal fired for the first time');
 
         try {
+            const sample = sink.pull_sample();
+            if (!sample) {
+                this._logger.debug('Live wallpaper: pull_sample() returned no sample');
+                return Gst.FlowReturn.OK;
+            }
+
             const buffer = sample.get_buffer();
             const structure = sample.get_caps().get_structure(0);
             const [, width] = structure.get_int('width');
             const [, height] = structure.get_int('height');
 
             const [ok, mapInfo] = buffer.map(Gst.MapFlags.READ);
-            if (!ok)
+            if (!ok) {
+                this._logger.debug('Live wallpaper: buffer.map() failed');
                 return Gst.FlowReturn.OK;
+            }
 
             try {
                 this._updateFrame(mapInfo.data, width, height);
@@ -210,7 +222,7 @@ export class LiveWallpaperManager {
                 buffer.unmap(mapInfo);
             }
         } catch (e) {
-            this._logger.error(e, 'Failed to process live wallpaper frame');
+            this._logger.error(e, 'Failed to process live wallpaper frame (new-sample handler)');
         }
 
         return Gst.FlowReturn.OK;