feat: undo last rating, customizable keys, and configurable text limit

A batch of self-contained user-facing improvements, squashed from the feat/org-drill-solo-features branch.

I added an undo for the last rating (issue #2 follow-up). The rating prompt now takes an undo key (org-drill--undo-key, default u): it restores the previous card's scheduling snapshot, drops the recorded quality, and re-queues that card, then returns to the current prompt. Each rating snapshots the scheduling properties and SCHEDULED line onto a per-session stack capped at org-drill-undo-limit (default 3). org-drill-reschedule loops on the rating read so undo doesn't rate the current card.

I made the five session-control keys (quit, edit, help, skip, tags) defcustoms so they can be rebound from customize-group (issue #35), keeping their defaults. The 0-5 rating keys stay as-is, since they're tied to the quality scale rather than being variables.

I lifted the hardcoded 100-line entry-text limit in org-drill-get-entry-text into the org-drill-entry-text-max-lines defcustom, defaulting to 100.

I also deleted a commented-out old org-entry-empty-p that the real definition had already replaced.

Existing tests stay green and each change added its own, including snapshot/restore and prompt-loop tests for undo.

1 files changed, 34 insertions, 0 deletions

diff --git a/tests/test-org-drill-entry-text-limit.el b/tests/test-org-drill-entry-text-limit.el
new file mode 100644
index 0000000..c9466cc
--- /dev/null
+++ b/tests/test-org-drill-entry-text-limit.el
@@ -0,0 +1,34 @@
+;;; test-org-drill-entry-text-limit.el --- Tests for the entry-text line limit  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; org-drill-get-entry-text asks org-agenda for at most N lines of an entry's
+;; text.  That limit used to be a hardcoded 100; it is now the defcustom
+;; org-drill-entry-text-max-lines so a user with very long cards can raise it.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(require 'org-drill)
+
+(ert-deftest test-org-drill-entry-text-max-lines-defaults-to-100 ()
+  "The limit keeps its historical default of 100 lines."
+  (should (eq 100 (default-value 'org-drill-entry-text-max-lines))))
+
+(ert-deftest test-org-drill-get-entry-text-uses-the-custom-limit ()
+  "get-entry-text passes the defcustom value as the line limit, not a
+hardcoded number."
+  (let ((org-drill-entry-text-max-lines 7)
+        (captured nil))
+    (cl-letf (((symbol-function 'org-agenda-get-some-entry-text)
+               (lambda (_marker n &rest _) (setq captured n) "text")))
+      (with-temp-buffer
+        (insert "* Card :drill:\nbody\n")
+        (org-mode)
+        (goto-char (point-min))
+        (org-drill-get-entry-text))
+      (should (eq 7 captured)))))
+
+(provide 'test-org-drill-entry-text-limit)
+
+;;; test-org-drill-entry-text-limit.el ends here