Add per-step resilience and notifications across all video pipeline scripts

Each pipeline now saves intermediate files permanently before the step most
likely to fail, so a partial failure leaves a recoverable artifact:
- daily_sunrise_video.sh: speed-adjusted video (*-sped.mp4) survives if the
  drawtext overlay step fails; deleted automatically on success
- montage-mvt.sh: speed-adjusted video (*-Sped.mp4) survives if the
  music-mux + attribution overlay step fails; deleted on success
- 4-seasons.sh / montage-mvt.sh / year-end-join.sh: explicit ffmpeg error
  handling with targeted notify.sh calls naming the failed step and the
  surviving artifact path
- montage-mvt.sh / 4-seasons.sh / year-end-join.sh: clip-duration-sum vs
  music-duration drift check warns when cumulative float error exceeds 2 s

https://claude.ai/code/session_01C4jbd3waXG3eKZYbGUjLUQ

4-seasons.sh

@@ -90,16 +90,32 @@ speed_factor=$(echo "scale=6; $raw_duration / $target_per_clip" | bc)
 echo "Step 2/2: speed factor $speed_factor..."
 
 final_file="$output_dir/${yesterday}_Mvt${MVT_NUM}-Day${DAY_OF_MVT}of${DAYS_IN_MVT}-final.mp4"
-ffmpeg -loglevel warning \
+if ! ffmpeg -loglevel warning \
     -i "$temp_video" \
     -vf "setpts=PTS/$speed_factor" \
     -c:v libx264 -pix_fmt yuv420p -crf "$CRF_SEASONS_FINAL" \
     -t "$target_per_clip" -an \
-    -y "$final_file"
+    -y "$final_file"; then
+    rm -f "$final_file"
+    "$SCRIPT_DIR/notify.sh" "FAILED: $SEASON Mvt$MVT_NUM Day$DAY_OF_MVT speed-adjust ($yesterday)" \
+        "ffmpeg speed-adjust failed — re-run 4-seasons.sh $CAM_NAME while JPGs exist" || true
+    exit 1
+fi
 
 adjusted=$(ffprobe -v error -show_entries format=duration -of csv=p=0 "$final_file")
 echo "Daily clip: $final_file  ($adjusted s)"
 
+# Warn if clip duration deviates more than 0.5 s from target (float drift check)
+drift=$(echo "scale=3; $adjusted - $target_per_clip" | bc | sed 's/^-//')
+if awk "BEGIN{exit !($drift > 0.5)}"; then
+    echo "WARNING: clip duration ${adjusted}s differs from target ${target_per_clip}s by ${drift}s"
+    "$SCRIPT_DIR/notify.sh" "WARNING: $SEASON Mvt$MVT_NUM Day$DAY_OF_MVT duration drift ($yesterday)" \
+        "Clip ${adjusted}s vs target ${target_per_clip}s (drift ${drift}s)" || true
+fi
+
+"$SCRIPT_DIR/notify.sh" "$SEASON Mvt$MVT_NUM Day$DAY_OF_MVT/$DAYS_IN_MVT saved ($yesterday)" \
+    "$(basename "$final_file") — ${adjusted}s" || true
+
 # ── Auto-trigger montage on last day of movement ──────────────────────────────
 if [ "$IS_LAST_DAY" = "true" ]; then
     echo "Last day of $SEASON Mvt $MVT_NUM — triggering montage compilation..."