feat(merge): preserve the user's view across a merge refresh

A merge refresh (the "merge keeping edits" choice on a dirty buffer, or pearl-refresh-current-view on a clean one) used to call pearl--restore-page-visibility at the tail, re-folding the whole buffer to its #+STARTUP overview. That collapsed every subtree the user had expanded, including the comment they were just editing, and disturbed point. The edit-then-merge flow felt jarring.

The fix: pearl--merge-issues-into-buffer now returns a marker for every subtree it re-rendered or appended, alongside the existing counts (:touched-markers (M1 M2 ...)). The merge call sites fold just those subtrees via a new pearl--fold-touched-subtrees helper. Kept (locally-edited) and untouched subtrees stay exactly as the user had them, and point is preserved because the localized fold doesn't touch the rest of the page.

The full-rebuild paths (Branch A no-buffer, Branch B clean-buffer replace, Branch C-discard) still call pearl--restore-page-visibility. They re-render the whole buffer so the global re-fold is the right behavior.

Pre-commit review caught a critical correctness bug in the first draft: the alist marker from pearl--issue-subtree-markers is insertion-type t (it needs to advance past replaces of EARLIER subtrees so it stays anchored to its own heading), and reusing it after pearl--replace-issue-subtree-at-point captured the post-advance position, which is the NEXT subtree's heading, so the fold collapsed the wrong subtree. The fix copies the marker as type-nil BEFORE the replace, so it stays anchored at the deletion start and lands on the new heading after the re-insert. I strengthened the marker test to verify the IDs at the touched markers match the expected set ({a, b, c} for 2 updated + 1 added), not just that they're some valid headings. The original test would have passed against the bug.

Five new tests in test-pearl-merge.el cover: merge returns markers with the correct IDs at their headings, skipped (locally-edited) issues don't add to touched-markers, fold-subtree-at-marker hides body content while leaving the heading visible, fold-touched-subtrees is a no-op when pearl-fold-after-update is nil, and fold-subtree-at-marker tolerates a nil marker silently. All 674 ert tests pass. make compile and make lint are clean.

1 files changed, 92 insertions, 0 deletions

diff --git a/tests/test-pearl-merge.el b/tests/test-pearl-merge.el
index 122e5fa..711e772 100644
--- a/tests/test-pearl-merge.el
+++ b/tests/test-pearl-merge.el
@@ -175,6 +175,98 @@ Merge must protect any locally-edited field, not only the description."
       (goto-char (point-min))
       (should (re-search-forward "UNPUSHED EDIT" nil t)))))
 
+;;; touched-markers + per-subtree fold
+
+(ert-deftest test-pearl-merge-returns-touched-markers-for-updated-and-added ()
+  "The merge result carries one marker per re-rendered or appended subtree.
+The marker list is the foundation of the per-subtree fold path that
+replaced the global re-fold: callers fold just the touched subtrees so
+an edit-then-merge flow leaves the rest of the page (and point) alone."
+  (test-pearl-merge--in-org
+      (test-pearl-merge--buffer (test-pearl-merge--issue "a" "Alpha" "Desc.")
+                                (test-pearl-merge--issue "b" "Beta" "Desc."))
+    (let* ((counts (pearl--merge-issues-into-buffer
+                    (list (test-pearl-merge--issue "a" "Alpha Renamed" "Desc.")
+                          (test-pearl-merge--issue "b" "Beta" "Desc.")
+                          (test-pearl-merge--issue "c" "Gamma" "Desc."))))
+           (markers (plist-get counts :touched-markers)))
+      ;; 2 updated + 1 added = 3 markers
+      (should (= 3 (length markers)))
+      ;; Every marker points at a live position in this buffer
+      (dolist (m markers)
+        (should (markerp m))
+        (should (eq (current-buffer) (marker-buffer m))))
+      ;; Each marker sits on or before an issue heading
+      (dolist (m markers)
+        (save-excursion
+          (goto-char m)
+          (org-back-to-heading t)
+          (should (org-entry-get nil "LINEAR-ID")))))))
+
+(ert-deftest test-pearl-merge-skipped-issues-do-not-add-to-touched-markers ()
+  "A locally-edited subtree the merge kept (skipped) is not in :touched-markers.
+The fold should leave kept subtrees exactly as the user had them, so they
+must not appear in the marker list the fold iterates."
+  (test-pearl-merge--in-org
+      (test-pearl-merge--buffer (test-pearl-merge--issue "a" "Alpha" "Desc Alpha.")
+                                (test-pearl-merge--issue "b" "Beta" "Desc Beta."))
+    ;; Mark the "a" subtree dirty by editing its description.
+    (goto-char (point-min))
+    (re-search-forward "Desc Alpha.")
+    (replace-match "Desc Alpha (locally edited).")
+    (let* ((counts (pearl--merge-issues-into-buffer
+                    (list (test-pearl-merge--issue "a" "Alpha" "Desc Alpha.")
+                          (test-pearl-merge--issue "b" "Beta Renamed" "Desc Beta."))))
+           (markers (plist-get counts :touched-markers)))
+      (should (= 1 (plist-get counts :skipped))) ; a was kept
+      (should (= 1 (plist-get counts :updated))) ; b was re-rendered
+      ;; Only one marker, and it sits on the "b" subtree.
+      (should (= 1 (length markers)))
+      (save-excursion
+        (goto-char (car markers))
+        (org-back-to-heading t)
+        (should (equal "b" (org-entry-get nil "LINEAR-ID")))))))
+
+;;; pearl--fold-subtree-at-marker
+
+(ert-deftest test-pearl-fold-subtree-at-marker-folds-heading-content ()
+  "Folding a subtree leaves the heading visible and hides the content."
+  (let ((pearl-fold-after-update t))
+    (test-pearl-merge--in-org
+        (test-pearl-merge--buffer (test-pearl-merge--issue "a" "Alpha" "Body line."))
+      (goto-char (point-min))
+      (re-search-forward "^\\*\\* ")
+      (beginning-of-line)
+      (let ((heading-pos (point)))
+        (pearl--fold-subtree-at-marker (copy-marker heading-pos))
+        ;; The heading itself is visible
+        (goto-char heading-pos)
+        (should-not (invisible-p (point)))
+        ;; A position inside the body is now invisible
+        (re-search-forward "Body line.")
+        (should (invisible-p (point)))))))
+
+(ert-deftest test-pearl-fold-touched-subtrees-no-op-when-disabled ()
+  "With `pearl-fold-after-update' nil, the fold helper does nothing."
+  (let ((pearl-fold-after-update nil))
+    (test-pearl-merge--in-org
+        (test-pearl-merge--buffer (test-pearl-merge--issue "a" "Alpha" "Body."))
+      (goto-char (point-min))
+      (re-search-forward "^\\*\\* ")
+      (beginning-of-line)
+      (let ((m (copy-marker (point))))
+        (pearl--fold-touched-subtrees (list m))
+        ;; Body stays visible
+        (re-search-forward "Body")
+        (should-not (invisible-p (point)))))))
+
+(ert-deftest test-pearl-fold-subtree-at-marker-tolerates-nil-marker ()
+  "A nil or dead marker is a silent no-op rather than erroring."
+  (let ((pearl-fold-after-update t))
+    (test-pearl-merge--in-org
+        (test-pearl-merge--buffer (test-pearl-merge--issue "a" "Alpha" "Body."))
+      (should-not (pearl--fold-subtree-at-marker nil)))))
+
 (ert-deftest test-pearl-merge-updates-rich-description-issue-in-place ()
   "An unedited issue with lossy markdown (a heading) is updated, not skipped.
 Regression: the dirty check round-tripped Org back to markdown and mistook a