fix: restore display state in the buffer setup ran in

org-drill--setup-display saved buffer-local state (mode-line,
variable-pitch-mode) into global defvars and called setq-local on
the current buffer.  org-drill--restore-display read those globals
and ran setq-local against whatever buffer happened to be current
at restore time.

If the user switched buffers mid-session, the restore wrote to the
wrong buffer — leaving the original drill buffer's mode-line still
hidden and trampling the destination buffer's mode-line with
whatever was saved from elsewhere.

Captured the buffer at setup in org-drill--saved-display-buffer.
Restore now wraps mode-line and variable-pitch restoration in
with-current-buffer against that saved buffer.  Text-scale stays
global (the underlying face attribute is process-wide).

1 files changed, 53 insertions, 0 deletions

diff --git a/tests/test-org-drill-display-restore.el b/tests/test-org-drill-display-restore.el
new file mode 100644
index 0000000..90d1b0d
--- /dev/null
+++ b/tests/test-org-drill-display-restore.el
@@ -0,0 +1,53 @@
+;;; test-org-drill-display-restore.el --- Regression for cross-buffer display restore  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; The display setup / restore pair saved buffer-local state (mode-line,
+;; variable-pitch-mode) to global defvars and restored via plain
+;; `setq-local'.  If the user switched buffers between setup and
+;; restore, the restore wrote to the wrong buffer — leaving the
+;; original drill buffer with its modeline still hidden, and trampling
+;; the destination buffer's modeline.
+;;
+;; The fix tracks the buffer at setup and uses `with-current-buffer'
+;; to restore in the original.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(require 'org)
+(require 'org-drill)
+
+;;;; Cross-buffer modeline restore
+
+(ert-deftest test-display-restore-modeline-in-original-buffer-after-buffer-switch ()
+  "Setup in buffer A, restore in buffer B — A's mode-line should be restored,
+B's mode-line untouched."
+  (let ((buffer-a (generate-new-buffer "*org-drill-test-A*"))
+        (buffer-b (generate-new-buffer "*org-drill-test-B*"))
+        (org-drill-hide-modeline-during-session t)
+        (org-drill-text-size-during-session nil)
+        (org-drill-use-variable-pitch nil))
+    (unwind-protect
+        (progn
+          (with-current-buffer buffer-a
+            (setq-local mode-line-format "A-original")
+            (org-drill--setup-display)
+            ;; A's modeline is now hidden (nil).
+            (should (null mode-line-format)))
+          (with-current-buffer buffer-b
+            (setq-local mode-line-format "B-original")
+            ;; Restore runs from buffer B (simulating a buffer switch
+            ;; mid-session).
+            (org-drill--restore-display))
+          ;; After restore: A's modeline back to original, B's untouched.
+          (with-current-buffer buffer-a
+            (should (equal "A-original" mode-line-format)))
+          (with-current-buffer buffer-b
+            (should (equal "B-original" mode-line-format))))
+      (kill-buffer buffer-a)
+      (kill-buffer buffer-b))))
+
+(provide 'test-org-drill-display-restore)
+
+;;; test-org-drill-display-restore.el ends here