diff --git a/lisp/build.el b/lisp/build.el
index b5be5c6..5529e81 100644
--- a/lisp/build.el
+++ b/lisp/build.el
@@ -11,12 +11,37 @@
 (package-initialize)
 
 (defvar site-root
-  (file-name-directory
-   (or load-file-name buffer-file-name)))
+  (let ((script-dir (file-name-directory
+                     (or load-file-name buffer-file-name))))
+    (file-name-as-directory
+     (expand-file-name
+      (if (string= (file-name-nondirectory
+                    (directory-file-name script-dir))
+                   "lisp")
+          ".."
+        ".")
+      script-dir))))
+
+(defconst z/build-start-time (float-time)
+  "Wall-clock time when the build started.")
 
 (defun site-path (path)
   (expand-file-name path site-root))
 
+(defun z/asset-version (path)
+  "Return a deterministic cache-busting version for asset PATH."
+  (let* ((file (site-path path))
+         (attrs (and (file-exists-p file) (file-attributes file)))
+         (mtime (and attrs (file-attribute-modification-time attrs)))
+         (size  (and attrs (file-attribute-size attrs))))
+    (if (and mtime size)
+        (format "%x-%x" (floor (float-time mtime)) size)
+      (format "%x" (floor z/build-start-time)))))
+
+(defun z/asset-url (path)
+  "Return root-relative asset PATH with a cache-busting query string."
+  (format "/%s?v=%s" path (z/asset-version path)))
+
 
 (unless package-archive-contents
   (package-refresh-contents))
@@ -138,26 +163,41 @@
 (add-to-list 'load-path default-directory)
 
 (defvar z-shared-head
-  "
-<link rel=\"icon\" type=\"image/png\" sizes=\"48x48\" href=\"/assets/icons/icons8-z-key-64.png\" />
+  (concat
+   "\n<link rel=\"icon\" type=\"image/png\" sizes=\"48x48\" href=\"/assets/icons/icons8-z-key-64.png\" />
 
-<link rel=\"stylesheet\" href=\"/assets/styles/style.css?v=20260514-search-modal\" />
-<link rel=\"stylesheet\" href=\"/assets/styles/bigger-picture.min.css\" />
-<link rel=\"stylesheet\" href=\"/assets/styles/media.css?v=20260514-search-modal\" />
-<link rel=\"stylesheet\" href=\"/assets/styles/cookbook.css\" />
+"
+   (mapconcat
+    (lambda (file)
+      (format "<link rel=\"stylesheet\" href=\"%s\" />"
+              (z/asset-url (format "assets/styles/%s" file))))
+    '("style.css"
+      "bigger-picture.min.css"
+      "media.css"
+      "cookbook.css")
+    "\n")
+   "
 
 <link rel=\"preconnect\" href=\"https://fonts.googleapis.com\" />
 <link rel=\"preconnect\" href=\"https://fonts.gstatic.com\" crossorigin />
 <link href=\"https://fonts.googleapis.com/css2?family=Noto+Sans+Arabic:wght@400;700&display=swap\" rel=\"stylesheet\" />
 
-<script src=\"/assets/scripts/script.js?v=20260514-search-modal\" defer></script> 
-<script src=\"/assets/scripts/search.js?v=20260514-search-modal\" defer></script> 
-<script src=\"/assets/scripts/bigger-picture.min.js\" defer></script>
-<script src=\"/assets/scripts/svg-pan-zoom.min.js\" defer></script>
-<script src=\"/assets/scripts/gallery-init.js\" defer></script>
-<script src=\"/assets/scripts/cookbook.js\" defer></script>
-
-<script src=\"/assets/scripts/mermaid.min.js\"></script>
+"
+   (mapconcat
+    (lambda (file)
+      (format "<script src=\"%s\" defer></script>"
+              (z/asset-url (format "assets/scripts/%s" file))))
+    '("script.js"
+      "search.js"
+      "bigger-picture.min.js"
+      "svg-pan-zoom.min.js"
+      "gallery-init.js"
+      "cookbook.js")
+    "\n")
+   "\n\n"
+   (format "<script src=\"%s\"></script>"
+           (z/asset-url "assets/scripts/mermaid.min.js"))
+   "
 
   <script>
     MathJax = {
@@ -263,7 +303,7 @@ window.mvOpen=function(el){
     });
   });
 </script>
-"
+")
   )
 
 (defvar z-preamble