feat(emacs): filter recurring events past CALDAV_UNTIL in agenda

DEADLINE doesn't actually limit recurring event display in org-agenda.
Instead, use org-agenda-skip-function-global to filter entries where
today's date is past the CALDAV_UNTIL property.

The skip function:
- Checks for CALDAV_UNTIL property (set by caldav sync advice)
- Parses YYYYMMDD format
- Skips entry if today > UNTIL date

This properly hides expired recurring events from the agenda.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

home/roles/emacs/doom/config.el

@@ -53,6 +53,22 @@
 ;; change `org-directory'. It must be set before org loads!
 (setq org-directory "~/org/")
 (after! org
+  ;; Skip recurring events past their CALDAV_UNTIL date
+  ;; org-caldav ignores UNTIL from RRULE, so we store it as a property
+  ;; and filter here in the agenda
+  (defun my/skip-if-past-until ()
+    "Return non-nil if entry has CALDAV_UNTIL and current date is past it."
+    (let ((until-str (org-entry-get nil "CALDAV_UNTIL")))
+      (when (and until-str
+                 (string-match "^\\([0-9]\\{4\\}\\)\\([0-9]\\{2\\}\\)\\([0-9]\\{2\\}\\)" until-str))
+        (let* ((until-year (string-to-number (match-string 1 until-str)))
+               (until-month (string-to-number (match-string 2 until-str)))
+               (until-day (string-to-number (match-string 3 until-str)))
+               (until-time (encode-time 0 0 0 until-day until-month until-year))
+               (today (current-time)))
+          (when (time-less-p until-time today)
+            (org-end-of-subtree t))))))
+
   (setq org-agenda-span 'week
         org-agenda-start-with-log-mode t
         my-agenda-dirs '("projects" "roam")
@@ -61,6 +77,7 @@
                                                                   "\.org$"))
                                                      my-agenda-dirs))
         org-log-done 'time
+        org-agenda-skip-function-global #'my/skip-if-past-until
         org-agenda-custom-commands '(("n" "Agenda"
                                       ((agenda "")
                                        (tags-todo "-someday-recurring")))