Fix scheduler timezone and taglib type errors

- cl-cron uses local time, not UTC: add utc-hour-to-local-hour
  conversion so schedule hours fire at correct UTC times
  (e.g. 12:00 UTC now fires at 15:00 local on UTC+3)

- Wrap each taglib field read in safe-tag with per-field error
  handling so a type error in one field (e.g. album with non-simple
  string) doesn't crash play-file or skip the track

- Use (coerce ... 'simple-string) instead of copy-seq for
  guaranteed simple-string output from ensure-simple-string

cl-streamer/harmony-backend.lisp

@@ -217,18 +217,25 @@
 ;;; ---- Metadata ----
 
 (defun ensure-simple-string (s)
-  "Coerce S to a simple-string if it's a string, or return NIL."
+  "Coerce S to a simple-string if it's a string, or return NIL.
+   Uses coerce to guarantee SIMPLE-STRING type for downstream consumers."
   (when (stringp s)
-    (copy-seq (string-trim '(#\Space #\Nul) s))))
+    (coerce (string-trim '(#\Space #\Nul) s) 'simple-string)))
+
+(defun safe-tag (fn audio-file)
+  "Safely read a tag field, coercing to simple-string. Returns NIL on any error."
+  (handler-case
+      (ensure-simple-string (funcall fn audio-file))
+    (error () nil)))
 
 (defun read-audio-metadata (file-path)
   "Read metadata (artist, title, album) from an audio file using taglib.
    Returns a plist (:artist ... :title ... :album ...) or NIL on failure."
   (handler-case
       (let ((audio-file (audio-streams:open-audio-file (namestring file-path))))
-        (list :artist (ensure-simple-string (abstract-tag:artist audio-file))
-              :title (ensure-simple-string (abstract-tag:title audio-file))
-              :album (ensure-simple-string (abstract-tag:album audio-file))))
+        (list :artist (safe-tag #'abstract-tag:artist audio-file)
+              :title (safe-tag #'abstract-tag:title audio-file)
+              :album (safe-tag #'abstract-tag:album audio-file)))
     (error (e)
       (log:debug "Could not read tags from ~A: ~A" file-path e)
       nil)))

playlist-scheduler.lisp

@@ -101,16 +101,30 @@
 
 ;;; Cron Job Management
 
+(defun utc-hour-to-local-hour (utc-hour)
+  "Convert a UTC hour (0-23) to the local timezone hour for cl-cron.
+   cl-cron uses decode-universal-time which returns local time."
+  (let* ((now (get-universal-time))
+         (local-hour (nth-value 2 (decode-universal-time now)))
+         (utc-hour-now (nth-value 2 (decode-universal-time now 0)))
+         (offset (- local-hour utc-hour-now)))
+    (mod (+ utc-hour offset) 24)))
+
 (defun setup-playlist-cron-jobs ()
-  "Set up cl-cron jobs for all scheduled playlists."
+  "Set up cl-cron jobs for all scheduled playlists.
+   Schedule hours are in UTC; cl-cron fires in local time,
+   so we convert UTC hours to local hours."
   (unless *scheduler-running*
     (dolist (entry *playlist-schedule*)
-      (let ((hour (car entry))
-            (playlist (cdr entry)))
+      (let* ((utc-hour (car entry))
+             (playlist (cdr entry))
+             (local-hour (utc-hour-to-local-hour utc-hour)))
+        (log:info "Scheduling ~A at ~2,'0d:00 UTC (~2,'0d:00 local)"
+                  playlist utc-hour local-hour)
         (cl-cron:make-cron-job 
-         (scheduled-playlist-loader hour playlist)
+         (scheduled-playlist-loader utc-hour playlist)
          :minute 0 
-         :hour hour)))
+         :hour local-hour)))
     (setf *scheduler-running* t)))
 
 (defun start-playlist-scheduler ()