fix: enforce kinsoku rules for CJK opening punctuation in box splitting

Opening brackets (（, 「, 《, etc.) are now attached to the following
character instead of the preceding one, preventing them from appearing
at the end of a line which violates kinsoku typographic rules.

Fixes #9

Agent-Logs-Url: https://github.com/Kinneyzhang/emacs-kp/sessions/d05069f4-db64-4601-9816-f582edad4a1b

Co-authored-by: Kinneyzhang <38454496+Kinneyzhang@users.noreply.github.com>

ekp-utils.el

@@ -115,6 +115,14 @@
         (and (>= char #x3000) (<= char #x303F))
         (and (>= char #xFF00) (<= char #xFF60)))))
 
+(defun ekp-cjk-opening-punct-p (str)
+  "Return non-nil if STR ends with a CJK opening punctuation.
+These characters must not appear at the end of a line (kinsoku rule).
+When STR is held as cjk-char, this checks if it still needs attachment."
+  (let ((char (aref str (1- (length str)))))
+    (memq (get-char-code-property char 'general-category)
+          '(Ps Pi))))
+
 (defun ekp--flush-latin-word (word boxes)
   "Push latin WORD to BOXES if non-nil. Return updated boxes."
   (if word (cons word boxes) boxes))
@@ -161,20 +169,41 @@ Return (new-state new-latin-word new-cjk-char new-boxes)."
       ;; Already in latin mode: accumulate
       (list 1 (concat latin-word str) nil boxes)
     ;; Was in CJK mode: flush CJK char, switch to latin
-    (list 1 str nil (ekp--flush-cjk-char cjk-char boxes))))
+    ;; If held cjk-char is opening punct, prepend it to the latin word
+    (if (and cjk-char (ekp-cjk-opening-punct-p cjk-char))
+        (list 1 (concat cjk-char str) nil boxes)
+      (list 1 str nil (ekp--flush-cjk-char cjk-char boxes)))))
 
 (defun ekp--handle-cjk-char (str state latin-word cjk-char boxes)
   "Handle a CJK (width=2) character.
 Return (new-state new-latin-word new-cjk-char new-boxes)."
   (if (= state 1)
       ;; Was in latin mode: flush latin word, push CJK directly
-      (list 2 nil nil (cons str (ekp--flush-latin-word latin-word boxes)))
+      (let ((new-boxes (ekp--flush-latin-word latin-word boxes)))
+        (if (ekp-cjk-opening-punct-p str)
+            ;; Opening punct: hold as cjk-char (will attach to next char)
+            (list 2 nil str new-boxes)
+          (list 2 nil nil (cons str new-boxes))))
     ;; Already in CJK mode
-    (if (ekp-cjk-fw-punct-p str)
-        ;; Punctuation attaches to previous CJK char
-        (list 2 nil nil (cons (concat cjk-char str) boxes))
-      ;; Regular CJK char: flush previous, hold current
-      (list 2 nil str (ekp--flush-cjk-char cjk-char boxes)))))
+    (cond
+     ((ekp-cjk-opening-punct-p str)
+      ;; Opening punct: cannot end a line (kinsoku rule).
+      ;; If previous held char is also opening punct, concatenate them.
+      ;; Otherwise flush previous and hold this opening punct.
+      (if (and cjk-char (ekp-cjk-opening-punct-p cjk-char))
+          (list 2 nil (concat cjk-char str) boxes)
+        (list 2 nil str (ekp--flush-cjk-char cjk-char boxes))))
+     ((ekp-cjk-fw-punct-p str)
+      ;; Closing/other punct: attaches to previous CJK char
+      (list 2 nil nil (cons (concat cjk-char str) boxes)))
+     (t
+      ;; Regular CJK char: prepend any held opening punct
+      (if (and cjk-char (ekp-cjk-opening-punct-p cjk-char))
+          ;; Previous was opening punct: combine with current char and hold.
+          ;; Now last char is regular, so this won't be detected as opening.
+          (list 2 nil (concat cjk-char str) boxes)
+        ;; Normal case: flush previous, hold current
+        (list 2 nil str (ekp--flush-cjk-char cjk-char boxes)))))))
 
 (defun ekp-split-to-boxes (string)
   "Split STRING into typographic boxes.
@@ -197,9 +226,12 @@ Whitespace runs are preserved as separate boxes; CJK punctuation attaches to pre
             (cond
              ;; Whitespace or zero-width: flush content, accumulate spaces
              ((or (string-blank-p str) (= 0 width))
-              (setq boxes (ekp--flush-cjk-char cjk-char boxes))
-              (when cjk-char (setq prev-state 2))
-              (setq cjk-char nil)
+              ;; Don't flush opening punct - keep it held for attachment to next char
+              (if (and cjk-char (ekp-cjk-opening-punct-p cjk-char))
+                  nil  ; keep cjk-char as-is
+                (setq boxes (ekp--flush-cjk-char cjk-char boxes))
+                (when cjk-char (setq prev-state 2))
+                (setq cjk-char nil))
               (setq boxes (ekp--flush-latin-word latin-word boxes))
               (when latin-word (setq prev-state 1))
               (setq latin-word nil)