fix(org-latex+corfu): filter-based tabularx, disable corfu-terminal on Emacs 31+

org-latex: replace before-processing-hook+insert with org-export-filter-table-functions.
  - Old approach (insert in hook) triggered org-element-cache after-change hooks
    causing infinite recursion / max-lisp-eval-depth even with inhibit-modification-hooks.
  - New: my/org-latex-table-to-tabularx filter transforms rendered LaTeX string,
    no buffer modification, no hook recursion possible.
  - Removed dead helpers: my/org-count-table-columns, my/org-table-attr-latex-spec.

corfu-terminal: add (< emacs-major-version 31) guard.
  - Emacs 31 supports corfu natively in terminal; corfu-terminal causes
    popup positioning issues (jumping) on Emacs 31+.

config.el

@@ -325,48 +325,27 @@ Bound to cmd+v in org-mode and markdown-mode."
 ;;; ORG MODE — LATEX EXPORT
 ;;; ============================================================
 
-;; Count data columns in an Org table line
-(defun my/org-count-table-columns (line)
-  "Count the number of data columns in Org table LINE."
-  (length (cl-remove-if
-           (lambda (s) (string-match-p "^-*$" (string-trim s)))
-           (cdr (butlast (split-string line "|"))))))
+;; LaTeX table export: replace tabular → tabularx{\textwidth}
+;; Filter approach: works on rendered LaTeX string, never touches the org buffer,
+;; so no hook recursion (the old before-processing-hook + insert approach caused
+;; 'max-lisp-eval-depth' via org-element-cache after-change hooks).
+(defun my/org-latex-table-to-tabularx (table _backend _info)
+  "Replace \\begin{tabular} with \\begin{tabularx}{\\textwidth} in LaTeX output."
+  (when (and (stringp table) (string-match "\\\\begin{tabular}" table))
+    (setq table (replace-regexp-in-string
+                 "\\\\begin{tabular}{\\([^}]*\\)}"
+                 "\\\\begin{tabularx}{\\\\textwidth}{\\1}"
+                 table))
+    (setq table (replace-regexp-in-string
+                 "\\\\end{tabular}"
+                 "\\\\end{tabularx}"
+                 table)))
+  table)
 
-;; Generate tabularx column spec: first column left-aligned, rest Y (auto-width)
-(defun my/org-table-attr-latex-spec (ncols)
-  "Return tabularx column spec for NCOLS columns: first l, rest Y."
-  (concat "l" (make-string (max 0 (1- ncols)) ?Y)))
-
-;; Automatically insert #+ATTR_LATEX tabularx before tables on LaTeX export
-(defun my/org-auto-tabularx (backend)
-  "Insert #+ATTR_LATEX tabularx before each table when exporting to LaTeX.
-Uses inhibit-modification-hooks to prevent recursive hook calls during insert."
-  (when (org-export-derived-backend-p backend 'latex)
-    (let ((inhibit-modification-hooks t))
-      (save-excursion
-        (goto-char (point-min))
-        (while (not (eobp))
-          (cond
-           ((looking-at "^|")
-            (let ((prev-line (save-excursion
-                               (forward-line -1)
-                               (buffer-substring-no-properties
-                                (line-beginning-position) (line-end-position)))))
-              (when (not (string-match-p "^|" prev-line))
-                (when (not (string-match-p "^#\\+ATTR_LATEX" prev-line))
-                  (let* ((table-line (buffer-substring-no-properties
-                                      (line-beginning-position) (line-end-position)))
-                         (ncols (my/org-count-table-columns table-line))
-                         (spec  (my/org-table-attr-latex-spec ncols))
-                         (attr  (format "#+ATTR_LATEX: :environment tabularx :width \\textwidth :align %s\n"
-                                        spec)))
-                    (when (> ncols 0)
-                      (insert attr)))))
-            (forward-line))
-           (t
-            (forward-line)))))))))
-
-(add-hook 'org-export-before-processing-hook #'my/org-auto-tabularx)
+(after! ox-latex
+  (add-to-list 'org-export-filter-table-functions
+               #'my/org-latex-table-to-tabularx)
+  (add-to-list 'org-latex-packages-alist '("" "tabularx")))
 
 ;; Optional: enable booktabs style (horizontal rules in tables)
 ;; (setq org-latex-tables-booktabs t)
@@ -561,9 +540,12 @@ and optional priority indicator [#A]."
   (add-hook 'prog-mode-hook #'martin/cape-capf-setup)
   (add-hook 'text-mode-hook #'martin/cape-capf-setup))
 
-;; Corfu popup in terminal (iTerm2 / SSH / tmux)
+;; Corfu popup in terminal — only needed for Emacs < 31 without child-frame support.
+;; Emacs 31 handles corfu natively even in terminal; loading corfu-terminal
+;; there causes popup positioning issues ("jumping").
 (use-package! corfu-terminal
-  :when (not (display-graphic-p))
+  :when (and (not (display-graphic-p))
+             (< emacs-major-version 31))
   :after corfu
   :config
   (corfu-terminal-mode +1))