Stop the AI from sorting hands in place; unskip full-game tests

Under Emacs 28 and earlier, sort relinks a list destructively, so the
variable that held the old head can end up holding only a tail.  Four
computer-player choices sorted a list that shared structure with the
player's stored hand (cl-remove-if-not returns its argument when it
removes nothing), so Bridge, Briscola, Pitch and Euchre dropped cards
from hands mid-deal and then stopped on (= nil N).  Emacs 29's sort
reorders in place, which hid the bug there.

The previous commit skipped cgt-bridge-full and cgt-trick-ext-full
unless SVG is available, but both render text in batch; they failed
on Emacs 27 for this reason, not for want of SVG.

* card-games-bridge.el (card-games-bridge--ai-play):
* card-games-trick-ext.el (card-games-tx--ai)
(card-games-trick--ai-play) <pitch>: Sort a copy, never the hand.
* test/card-games-tests.el (cgt-bridge-full, cgt-trick-ext-full):
Drop the SVG skip.
(cgt--hands-snapshot, cgt-ai-play-leaves-hands-alone): New test; it
fails without the fix on Emacs 27 and on Emacs 29.
* NEWS: Note the fix.

Assisted-by: Mentat (for Corwin; claude-opus-5-5)

NEWS

@@ -3,6 +3,16 @@ card-games NEWS  -- user-visible changes
 
 * Version 1.0.92 (pretest3: MELPA review)
 
+** Bug fixes
+  - Bridge, Briscola, Pitch and Euchre no longer lose cards from a
+    hand part-way through a deal under Emacs 28 and earlier.  The
+    computer players sorted a list that shared structure with the
+    hand; ~sort~ before Emacs 29 relinks the list, which cut cards
+    out of the hand and later stopped play with a type error.  Emacs
+    29 and later were unaffected.  The full-game Bridge and trick
+    tests no longer skip without SVG, and a new test checks that a
+    computer player's choice leaves every hand unchanged.
+
 ** Packaging and internals
   - card-games-net requires subr-x.  It calls ~string-empty-p~, which
     lives in subr-x before Emacs 29, so a fresh Emacs 27 failed every

card-games-bridge.el

@@ -417,7 +417,7 @@ vulnerability, and TRICKS the declarer side's trick count.  Keys:
          ((and partner (>= (length trick) 1))
           (car (sort (copy-sequence legal) (lambda (a b) (< (cdr a) (cdr b))))))
          ;; can win: take it with the cheapest winner
-         (winners (car (sort winners (lambda (a b) (< (cdr a) (cdr b))))))
+         (winners (car (sort (copy-sequence winners) (lambda (a b) (< (cdr a) (cdr b))))))
          ;; cannot win: discard lowest
          (t (car (sort (copy-sequence legal) (lambda (a b) (< (cdr a) (cdr b)))))))))))
 

card-games-trick-ext.el

@@ -98,9 +98,9 @@ POWERFN, LEDFN rank cards; VALUEFN gives a card's point worth."
                                      trump powerfn ledfn))
               (push c winners) (push c losers)))
         (if winners
-            (car (sort winners (lambda (a b) (< (funcall powerfn a trump led)
+            (car (sort (copy-sequence winners) (lambda (a b) (< (funcall powerfn a trump led)
                                                 (funcall powerfn b trump led)))))
-          (car (sort (or losers legal)
+          (car (sort (copy-sequence (or losers legal))
                      (lambda (a b) (< (funcall valuefn a) (funcall valuefn b))))))))))
 
 (defun card-games-tx--plain-led (card _trump) "Return CARD's suit (the plain led suit)." (car card))
@@ -236,8 +236,8 @@ SEAT plays CARD as usual once trump is fixed."
         (dotimes (s 4)
           (let ((v (card-games-pitch--suit-strength game seat s)))
             (when (> v bestv) (setq bestv v best s))))
-        (car (sort (cl-remove-if-not (lambda (c) (= (car c) best))
-                                     (card-games-trick--hand game seat))
+        (car (sort (copy-sequence (cl-remove-if-not (lambda (c) (= (car c) best))
+                                     (card-games-trick--hand game seat)))
                    (lambda (a b) (> (cdr a) (cdr b))))))
     (card-games-tx--ai game seat #'card-games-pitch--power #'card-games-tx--plain-led
                (lambda (c) (card-games-pitch--pip (cdr c))))))

test/card-games-tests.el

@@ -1570,7 +1570,6 @@ left a 15-card hand in play."
                                   (setq s (+ s (card-games-bris--points (cons su r)))))) s))))
 
 (ert-deftest cgt-trick-ext-full ()
-  (skip-unless (image-type-available-p 'svg))
   (dolist (class '(card-games-briscola-game card-games-pitch-game card-games-euchre-game))
     (let ((g (make-instance class)) (guard 0))
       (card-games-trick--new g)
@@ -1618,7 +1617,6 @@ left a 15-card hand in play."
                 '((0 . (0 . 12)) (1 . (3 . 0)) (2 . (0 . 2)) (3 . (0 . 5))) 3))))
 
 (ert-deftest cgt-bridge-full ()
-  (skip-unless (image-type-available-p 'svg))
   (let ((scored 0) (passed 0))
     (dotimes (i 12)
       (let ((g (card-games-bridge-game)) (guard 0))
@@ -1641,6 +1639,48 @@ left a 15-card hand in play."
         (should (memq (card-games-get g :phase) '(scored passed-out)))
         (should (stringp (card-games-render g)))))
     (should (> scored 0))))
+;;;; AI choice leaves the hands alone
+
+(defun cgt--hands-snapshot (g)
+  "Return a deep copy of G's :hands, for comparing before and after."
+  (mapcar #'copy-sequence (append (card-games-get g :hands) nil)))
+
+(ert-deftest cgt-ai-play-leaves-hands-alone ()
+  "Choosing a card must neither reorder nor shorten any hand.
+A destructive `sort' on a list that shares structure with a hand
+drops cards from it under Emacs 28 and earlier, and reorders it in
+place under Emacs 29 and later; this catches both."
+  ;; Bridge
+  (dotimes (i 4)
+    (let ((g (card-games-bridge-game)) (guard 0))
+      (card-games-put g :dealer i)
+      (card-games-bridge--deal g)
+      (while (and (eq (card-games-get g :phase) 'auction) (< guard 60))
+        (cl-incf guard)
+        (let* ((s (card-games-get g :bidder)) (call (card-games-bridge--ai-call g s)))
+          (unless (card-games-bridge--legal-call-p g call) (setq call 'pass))
+          (card-games-bridge--apply-call g s call)
+          (card-games-bridge--auction-done-p g)))
+      (let ((p 0))
+        (while (and (eq (card-games-get g :phase) 'play) (< p 60))
+          (cl-incf p)
+          (let* ((s (card-games-get g :turn)) (before (cgt--hands-snapshot g))
+                 (c (card-games-bridge--ai-play g s)))
+            (should (equal before (cgt--hands-snapshot g)))
+            (card-games-bridge--play-card g s c))))))
+  ;; Briscola, Pitch, Euchre
+  (dolist (class '(card-games-briscola-game card-games-pitch-game card-games-euchre-game))
+    (let ((g (make-instance class)) (guard 0))
+      (card-games-trick--new g)
+      (while (and (not (eq (card-games-get g :phase) 'game-over)) (< guard 400))
+        (cl-incf guard)
+        (if (card-games-trick--hand-over-p g)
+            (card-games-trick--finish-hand g)
+          (let* ((s (card-games-get g :turn)) (before (cgt--hands-snapshot g))
+                 (c (card-games-trick--ai-play g s)))
+            (should (equal before (cgt--hands-snapshot g)))
+            (card-games-trick--play g s c)))))))
+
 ;;;; Renderer registry / region keystone
 
 (ert-deftest cgt-keystone-regions ()