debug: log SSE data shape and fix misleading success:false log

msg.success doesn't exist in Gradio 5 SSE protocol — completion/error
is signalled via msg.output.error. Log the actual error field and dump
out.data[0]/[1] shape so we can verify the video URL extraction path.

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

app.py

@@ -2128,6 +2128,8 @@ _GLOBAL_JS = """
       if (msg.msg === 'process_generating' || msg.msg === 'process_completed') {
         var out = msg.output;
         if (out && out.data) {
+          console.log('[fireRegen] SSE data[0]:', JSON.stringify(out.data[0]).slice(0,200),
+                      ' data[1]:', JSON.stringify(out.data[1]).slice(0,80));
           // data[0] = video update, data[1] = waveform HTML update
           var vidUpdate  = out.data[0];
           var waveUpdate = out.data[1];
@@ -2174,7 +2176,8 @@ _GLOBAL_JS = """
           var lbl = document.getElementById('wf_seglabel_' + slot_id);
           if (lbl) lbl.textContent = msg.output && msg.output.error ?
             'Error regenerating' : 'Done';
-          console.log('[fireRegen] completed for', slot_id, 'success:', msg.success);
+          var hadError = !!(msg.output && msg.output.error);
+          console.log('[fireRegen] completed for', slot_id, 'error:', hadError, msg.output && msg.output.error || '');
 
           // Apply video src AFTER Gradio/Svelte finishes its own re-render cycle.
           // We try at 50ms, 300ms, and 800ms to catch whenever Svelte settles.