fix(comments): render padded dividers at LENGTH exactly

available-width omitted the doubled semicolon and the space after comment-start that the emit path adds, so dividers rendered LENGTH+2 (elisp) or LENGTH+1 wide. The budget now mirrors every term min-length already counts.

2 files changed, 23 insertions, 0 deletions

diff --git a/modules/custom-comments.el b/modules/custom-comments.el
index 73d29b0c..7f66424c 100644
--- a/modules/custom-comments.el
+++ b/modules/custom-comments.el
@@ -200,8 +200,13 @@ PADDING is the number of spaces before the text."
                        (if (string-empty-p cmt-end) 0 (1+ (length cmt-end))))))
     (when (< length min-length)
       (error "Length %d is too small to generate comment (minimum %d)" length min-length))
+    ;; Mirror every term the emit path adds: the prologue also inserts a
+    ;; doubled semicolon (elisp) and a trailing space that this budget used
+    ;; to omit, rendering dividers LENGTH+2 (elisp) or LENGTH+1 wide.
     (let* ((available-width (- length current-column-pos
                               (length cmt-start)
+                              (if (equal cmt-start ";") 1 0)  ; doubled semicolon
+                              1  ; space after comment-start
                               (if (string-empty-p cmt-end) 0 (1+ (length cmt-end)))))
            (line (make-string available-width (string-to-char decoration-char))))
       ;; Top line
diff --git a/tests/test-custom-comments-comment-padded-divider.el b/tests/test-custom-comments-comment-padded-divider.el
index d4c18905..9f2b4fd7 100644
--- a/tests/test-custom-comments-comment-padded-divider.el
+++ b/tests/test-custom-comments-comment-padded-divider.el
@@ -246,5 +246,23 @@ Returns the buffer string for assertions."
     ;; Should include comment-end
     (should (string-match-p "\\*/" result))))
 
+;;; Rendered width honors LENGTH exactly
+
+(ert-deftest test-padded-divider-width-matches-length-exactly ()
+  "Normal: each decoration line renders exactly LENGTH wide.
+available-width forgot the doubled semicolon (elisp) and the space after
+comment-start that the emit path adds, so dividers rendered LENGTH+2
+(elisp) or LENGTH+1 wide, contradicting the docstring."
+  ;; elisp: lone ";" doubles to ";;" plus a space
+  (let* ((result (test-padded-divider-at-column 0 ";" "" "-" "x" 40 1))
+         (lines (split-string result "\n" t)))
+    (should (= 40 (length (car lines))))
+    (should (= 40 (length (car (last lines))))))
+  ;; c-style with an end delimiter and no doubling
+  (let* ((result (test-padded-divider-at-column 0 "/*" "*/" "-" "x" 40 1))
+         (lines (split-string result "\n" t)))
+    (should (= 40 (length (car lines))))
+    (should (= 40 (length (car (last lines)))))))
+
 (provide 'test-custom-comments-comment-padded-divider)
 ;;; test-custom-comments-comment-padded-divider.el ends here