Fix complete-without-start hang for ultra-short tracks; add Opus rebuffer hysteresis

Tracks whose total audio falls below the playback-start threshold (Opus <1s lead, WAV <6 buffers) silently hung loaded-but-not-playing. After MarkStreamCompleteAsync, call TryStartPlaybackAsync when _streamingPlaybackStarted is still false so the scheduler drains its buffers and fires onPlaybackEnded exactly once.

DeepDrftPublic/Interop/audio/AudioPlayer.ts

@@ -285,10 +285,15 @@ export class AudioPlayer {
                 return { success: false, error: 'Opus decode failed' };
             }
 
-            // "headerParsed" maps to the decoder being configured (codec ready). canStart needs the
-            // min buffer count, exactly as the WAV path requires before first playback.
+            // "headerParsed" maps to the decoder being configured (codec ready). canStart needs a
+            // healthy decoded lead before first playback — measured in SECONDS, not a buffer count.
+            // An Opus WebCodecs packet is ~20 ms, so the WAV-tuned 6-BUFFER minimum is only ~0.12 s of
+            // lead: playback would start, drain it before the async decode ramps, and underrun
+            // immediately. The seconds-based lead gate (same threshold the scheduler's underrun-resume
+            // hysteresis uses) gives Opus the cushion its decode ramp needs. WAV keeps the buffer-count
+            // gate below — its large synchronous segments rarely underrun and its start must not change.
             const headerParsed = decoder.ready;
-            const canStart = headerParsed && this.scheduler.hasMinimumBuffers(this.minBuffersForPlayback);
+            const canStart = headerParsed && this.scheduler.hasMinimumPlaybackLead();
 
             return {
                 success: true,