docs: keep the org-element cache reproduction evidenceHEADmain

Twelve scripts plus a README covering the persist-write cache corruption:
the no-dirvish root cause, the buffer-list ordering dependency, a faithful
replay of the file-manager preview path, and the two fixes I tried and
reverted.

The README says which scripts are weak evidence and why, so the next reader
doesn't rebuild an argument on the one whose control varied three things at
once.

Also holds the upstream bug report and its reproduction, verified to run
standalone under emacs -Q.

1 files changed, 76 insertions, 0 deletions

diff --git a/working/org-element-cache-persist-bug/hostile-a-errorbranch.el b/working/org-element-cache-persist-bug/hostile-a-errorbranch.el
new file mode 100644
index 00000000..88711787
--- /dev/null
+++ b/working/org-element-cache-persist-bug/hostile-a-errorbranch.el
@@ -0,0 +1,76 @@
+;;; hostile-a-errorbranch.el --- attack the dirvish.el:680 error branch -*- lexical-binding: t -*-
+
+;; dirvish--preview-file-maybe-truncate (dirvish.el:671-680) wraps
+;;   (set-auto-mode) (font-lock-mode 1) (and so-long-detected-p (error ...))
+;; in a condition-case.  On ANY error the buffer is KILLED at line 680 and
+;; `dirvish-preview-setup-hook' at line 682 is NEVER reached.  By then
+;; set-auto-mode has already put the buffer in org-mode with buffer-file-name
+;; pointing at the real file.  So the shipped fix cannot run on that path.
+
+(require 'org) (require 'org-element) (require 'org-persist)
+(add-to-list 'load-path (expand-file-name "modules" default-directory))
+(require 'dirvish-config)
+
+(setq org-element-use-cache t
+      org-element-cache-persistent t
+      org-element--cache-self-verify t
+      org-element--cache-self-verify-frequency 1.0)
+
+(defun h--walk (buf)
+  (with-current-buffer buf
+    (org-element-cache-map (lambda (_e) nil) :granularity 'element)
+    (and org-element--cache (avl-tree-size org-element--cache))))
+
+;; Faithful replay of dirvish.el:657-684, including the condition-case and the
+;; error-branch kill.  ERROR-INJECT non-nil simulates so-long-detected-p / any
+;; other signal raised AFTER set-auto-mode has entered org-mode.
+(defun h--preview (file error-inject)
+  (with-current-buffer (get-buffer-create "*preview-temp*")
+    (let ((threshold 1048576) info jka-compr-verbose)
+      (with-silent-modifications
+        (setq buffer-read-only t)
+        (insert-file-contents file nil 0 threshold)
+        (setq buffer-file-name file)
+        (goto-char (point-min))
+        (rename-buffer (format "PREVIEW :: 999 :: %s" (file-name-nondirectory file))))
+      (condition-case err
+          (let ((enable-dir-local-variables nil) (enable-local-variables :safe)
+                (non-essential t) (inhibit-message t))
+            (setq-local delay-mode-hooks t)
+            (set-auto-mode) (font-lock-mode 1)
+            (and error-inject (error "No preview of file with long lines")))
+        (error (setq info (error-message-string err))))
+      (message "  preview: mode=%s file=%s persist-local=%s registered-kill-hook=%s"
+               major-mode (and buffer-file-name t)
+               (local-variable-p 'org-element-cache-persistent)
+               (and (memq 'org-persist-write-all-buffer kill-buffer-hook) t))
+      (if info
+          (progn (message "  ERROR BRANCH taken (%s) -> kill WITHOUT hook" info)
+                 (let (kill-buffer-query-functions) (kill-buffer (current-buffer))))
+        (run-hooks 'dirvish-preview-setup-hook)
+        (message "  ok branch: hook ran, persist-local=%s value=%s"
+                 (local-variable-p 'org-element-cache-persistent)
+                 org-element-cache-persistent)
+        (let (kill-buffer-query-functions) (kill-buffer (current-buffer)))))))
+
+(defun h--trial (label error-inject)
+  (let* ((src (expand-file-name "todo.org" default-directory))
+         (file (make-temp-file "hostile-" nil ".org")))
+    (copy-file src file t)
+    (message "== %s ==" label)
+    (let ((real (find-file-noselect file)))
+      (message "  real cache: %S" (h--walk real))
+      (h--preview file error-inject)
+      (with-current-buffer real
+        (goto-char (point-max))
+        (condition-case err
+            (progn (let ((inhibit-read-only t)) (insert "\n* Hostile edit\n"))
+                   (org-element-cache-map (lambda (_e) nil) :granularity 'element)
+                   (message "  RESULT: CLEAN (size=%S)" (avl-tree-size org-element--cache)))
+          (error (message "  RESULT: CORRUPT -> %S" err)))
+        (set-buffer-modified-p nil))
+      (let (kill-buffer-query-functions) (kill-buffer real)))
+    (delete-file file)))
+
+(h--trial "control: no error, hook runs (shipped fix active)" nil)
+(h--trial "attack: error after set-auto-mode -> hook skipped" t)