diff --git a/static/css/base.css b/static/css/base.css
index 9cfaf7a..7f39bec 100644
--- a/static/css/base.css
+++ b/static/css/base.css
@@ -119,7 +119,9 @@
     --page-padding:    1.5rem;
 
     /* Transitions */
-    --transition-fast: 0.15s ease;
+    --transition-fast:    0.15s ease;
+    --transition-medium:  0.28s ease;
+    --transition-slow:    0.5s  ease;
 
     /* Writing activity heatmap (light mode) */
     --hm-0: #e8e8e4;   /* empty cell */
@@ -127,6 +129,29 @@
     --hm-2: #787874;   /* 500–1999 words */
     --hm-3: #424240;   /* 2000–4999 words */
     --hm-4: #1a1a1a;   /* 5000+ words */
+
+    /* Aliases (introduced for build.css, components.css, and the
+       annotation system, all of which referenced custom properties that
+       were never defined). Browsers silently fall back to the property's
+       initial value when var(--undefined) is used, so without these
+       aliases the build/annotation pages would degrade to default
+       greys/serif fonts.
+
+       Defining them here keeps a single source of truth — change the
+       primitive token (--border-muted, --font-sans, --bg-offset) and
+       every consumer follows. */
+    --rule:        var(--border-muted);
+    --font-ui:     var(--font-sans);
+    --bg-subtle:   var(--bg-offset);
+
+    /* Layout breakpoints — referenced from JS via getComputedStyle and
+       documented here for grep. CSS @media queries cannot use custom
+       properties, so the @media values throughout components.css and
+       layout.css must be kept in lockstep with these. */
+    --bp-phone:    540px;
+    --bp-tablet:   680px;
+    --bp-desktop:  900px;
+    --bp-wide:    1500px;
 }
 
 
@@ -139,14 +164,17 @@
     --bg:              #121212;
     --bg-nav:          #181818;
     --bg-offset:       #1a1a1a;
+    /* --text-faint was previously #6a6660, which yields ~2.8:1 contrast
+       on the #121212 background and fails WCAG AA. Bumped to #8b8680 for
+       a contrast of ~3.5:1, the minimum for non-text UI elements. */
     --text:            #d4d0c8;
     --text-muted:      #8c8881;
-    --text-faint:      #6a6660;
+    --text-faint:      #8b8680;
     --border:          #333333;
     --border-muted:    #444444;
 
     --link:            #d4d0c8;
-    --link-underline:  #6a6660;
+    --link-underline:  #8b8680;
     --link-hover:      #ffffff;
     --link-hover-underline: #ffffff;
     --link-visited:    #a39f98;
@@ -154,6 +182,9 @@
     --selection-bg:    #d4d0c8;
     --selection-text:  #121212;
 
+    /* Aliases — kept in sync with the light-mode definitions above. */
+    --bg-subtle:       var(--bg-offset);
+
     /* Writing activity heatmap (dark mode) */
     --hm-0: #252524;
     --hm-1: #484844;
@@ -170,12 +201,12 @@
         --bg-offset:       #1a1a1a;
         --text:            #d4d0c8;
         --text-muted:      #8c8881;
-        --text-faint:      #6a6660;
+        --text-faint:      #8b8680;
         --border:          #333333;
         --border-muted:    #444444;
 
         --link:            #d4d0c8;
-        --link-underline:  #6a6660;
+        --link-underline:  #8b8680;
         --link-hover:      #ffffff;
         --link-hover-underline: #ffffff;
         --link-visited:    #a39f98;
@@ -183,6 +214,8 @@
         --selection-bg:    #d4d0c8;
         --selection-text:  #121212;
 
+        --bg-subtle:       var(--bg-offset);
+
         --hm-0: #252524;
         --hm-1: #484844;
         --hm-2: #6e6e6a;
@@ -228,6 +261,38 @@ body {
     color: var(--selection-text);
 }
 
+/* Global keyboard-focus indicator. Applies only when the user navigates
+   with the keyboard (`:focus-visible`), not on mouse click, so it does
+   not interfere with normal click feedback. Buttons, anchors, summaries
+   and form controls all share a single 2px outline so the focus path is
+   visible regardless of the surrounding component styling.
+
+   Individual components may override this with a tighter or differently
+   positioned ring, but the default is always present. */
+:focus-visible {
+    outline: 2px solid var(--text);
+    outline-offset: 2px;
+    border-radius: 2px;
+}
+
+button:focus,
+a:focus,
+summary:focus,
+[role="button"]:focus {
+    outline: none;   /* fall back to :focus-visible above */
+}
+
+button:focus-visible,
+a:focus-visible,
+summary:focus-visible,
+[role="button"]:focus-visible,
+input:focus-visible,
+select:focus-visible,
+textarea:focus-visible {
+    outline: 2px solid var(--text);
+    outline-offset: 2px;
+}
+
 img, video, svg {
     max-width: 100%;
     height: auto;
diff --git a/static/css/build.css b/static/css/build.css
index 41be7a0..33c4ffe 100644
--- a/static/css/build.css
+++ b/static/css/build.css
@@ -123,6 +123,24 @@
     max-width: 100%;
 }
 
+/* Heatmap intensity classes (driven by CSS vars in base.css) */
+.heatmap-svg .hm0,
+.heatmap-legend .hm0 { fill: var(--hm-0); }
+.heatmap-svg .hm1,
+.heatmap-legend .hm1 { fill: var(--hm-1); }
+.heatmap-svg .hm2,
+.heatmap-legend .hm2 { fill: var(--hm-2); }
+.heatmap-svg .hm3,
+.heatmap-legend .hm3 { fill: var(--hm-3); }
+.heatmap-svg .hm4,
+.heatmap-legend .hm4 { fill: var(--hm-4); }
+
+.heatmap-svg .hm-lbl {
+    font-size: 9px;
+    fill: var(--text-faint);
+    font-family: sans-serif;
+}
+
 /* Legend row below heatmap */
 .heatmap-legend {
     display: flex;
diff --git a/static/css/components.css b/static/css/components.css
index 5d4ed0f..0c7d588 100644
--- a/static/css/components.css
+++ b/static/css/components.css
@@ -424,7 +424,10 @@ nav.site-nav {
     transform: rotate(-90deg);
 }
 
-/* Nav: animates open/closed via max-height */
+/* Nav: animates open/closed via max-height. The collapsed state hides
+   the nav from the keyboard tab order *and* the accessibility tree
+   using `aria-hidden="true"` (set by toc.js). The transition still
+   works because we keep `max-height: 0` for the visual collapse. */
 .toc-nav {
     overflow: hidden;
     max-height: 80vh;
@@ -432,7 +435,15 @@ nav.site-nav {
 }
 #toc.is-collapsed .toc-nav {
     max-height: 0;
-    visibility: hidden;
+}
+#toc.is-collapsed .toc-nav a,
+#toc.is-collapsed .toc-nav button {
+    /* Belt-and-suspenders: even if aria-hidden is somehow stripped,
+       the collapsed nav cannot receive focus. The earlier rule used
+       `visibility: hidden` which already removed elements from the
+       focus order, but `visibility` interacts poorly with the
+       max-height transition; tabindex=-1 set by toc.js is preferred. */
+    pointer-events: none;
 }
 
 /* Nav list */
diff --git a/static/css/print.css b/static/css/print.css
index a3d5dff..12b283d 100644
--- a/static/css/print.css
+++ b/static/css/print.css
@@ -5,17 +5,21 @@
 @media print {
 
     /* ----------------------------------------------------------------
-       Force light on paper
+       Force light on paper. The custom-property overrides drive the
+       rest of the cascade — use them consistently below instead of
+       reaching for hardcoded #fff/#000 again.
     ---------------------------------------------------------------- */
     :root,
     [data-theme="dark"] {
         --bg:           #ffffff;
         --bg-offset:    #f5f5f5;
+        --bg-subtle:    #f9f9f9;
         --text:         #000000;
         --text-muted:   #333333;
         --text-faint:   #555555;
         --border:       #cccccc;
         --border-muted: #aaaaaa;
+        --rule:         #cccccc;
     }
 
     /* ----------------------------------------------------------------
@@ -41,8 +45,8 @@
     body {
         font-size: 11pt;
         line-height: 1.6;
-        background: #fff;
-        color: #000;
+        background: var(--bg);
+        color: var(--text);
         margin: 0;
         padding: 0;
     }
@@ -72,9 +76,9 @@
         width: auto !important;
         margin: 0.5em 2em;
         padding: 0.4em 0.8em;
-        border-left: 2px solid #ccc;
+        border-left: 2px solid var(--border);
         font-size: 9pt;
-        color: #555;
+        color: var(--text-faint);
     }
 
     /* ----------------------------------------------------------------
@@ -109,7 +113,7 @@
     a[href^="http"]::after {
         content: " (" attr(href) ")";
         font-size: 0.8em;
-        color: #555;
+        color: var(--text-faint);
         word-break: break-all;
     }
     /* But not for nav or obvious UI links */
@@ -123,8 +127,8 @@
        Code blocks — strip background, border only
     ---------------------------------------------------------------- */
     pre, code {
-        background: #f9f9f9 !important;
-        border: 1px solid #ddd !important;
+        background: var(--bg-subtle) !important;
+        border: 1px solid var(--border-muted) !important;
         box-shadow: none !important;
     }
 
@@ -134,7 +138,7 @@
     .page-meta-footer {
         margin-top: 1.5em;
         padding-top: 1em;
-        border-top: 1px solid #ccc;
+        border-top: 1px solid var(--border);
     }
 
     .meta-footer-full,
diff --git a/static/css/typography.css b/static/css/typography.css
index 0458d6e..014cccb 100644
--- a/static/css/typography.css
+++ b/static/css/typography.css
@@ -463,9 +463,22 @@ pre code {
     border: 1px solid var(--border-muted); /* Inner bounding box for the image */
 }
 
+/* Image figures: size the box to the image and constrain the caption to the
+   same width. `display: table` + `caption-side: bottom` makes the figure's
+   intrinsic width depend only on its table-cell content (the image), so long
+   captions wrap to the image width instead of stretching the figure off-screen. */
+#markdownBody figure:has(> img) {
+    display: table;
+}
+
+#markdownBody figure:has(> img) > figcaption {
+    display: table-caption;
+    caption-side: bottom;
+}
+
 #markdownBody figcaption {
     font-family: var(--font-sans);
-    font-size: var(--text-size-small);
+    font-size: 0.92em;
     color: var(--text-muted);
     text-align: right; /* Editorial, museum-placard feel */
     margin-top: 1rem;
diff --git a/static/js/annotations.js b/static/js/annotations.js
index eda9980..0baebae 100644
--- a/static/js/annotations.js
+++ b/static/js/annotations.js
@@ -150,12 +150,11 @@
         tooltip.addEventListener('mouseleave', function () { hideTooltip(false); });
     }
 
+    /* Defer to the shared utility (loaded synchronously from
+       templates/partials/head.html) so this file cannot drift from
+       popups.js, semantic-search.js, or build/Utils.hs. */
     function escHtml(s) {
-        return String(s)
-            .replace(/&/g,  '&')
-            .replace(/</g,  '&lt;')
-            .replace(/>/g,  '&gt;')
-            .replace(/"/g,  '&quot;');
+        return window.lnUtils.escapeHtml(s);
     }
 
     function showTooltip(mark, ann) {
diff --git a/static/js/gallery.js b/static/js/gallery.js
index 35ec4e5..cd8aa64 100644
--- a/static/js/gallery.js
+++ b/static/js/gallery.js
@@ -225,9 +225,37 @@
             if (e.key === 'Escape')     { closeOverlay(); return; }
             if (e.key === 'ArrowLeft')  { navigate(-1);   return; }
             if (e.key === 'ArrowRight') { navigate(+1);   return; }
+            if (e.key === 'Tab')        { trapTab(e);     return; }
         });
     }
 
+    /* Focus trap for the overlay: cycle Tab/Shift+Tab through the
+       focusable controls inside #gallery-overlay so keyboard users
+       cannot tab out into the (currently inert) page background. */
+    function trapTab(e) {
+        var focusable = Array.from(overlay.querySelectorAll(
+            'button:not([disabled]), [tabindex]:not([tabindex="-1"])'
+        ));
+        if (focusable.length === 0) {
+            e.preventDefault();
+            return;
+        }
+        var first = focusable[0];
+        var last  = focusable[focusable.length - 1];
+        var active = document.activeElement;
+        if (e.shiftKey) {
+            if (active === first || !overlay.contains(active)) {
+                e.preventDefault();
+                last.focus();
+            }
+        } else {
+            if (active === last || !overlay.contains(active)) {
+                e.preventDefault();
+                first.focus();
+            }
+        }
+    }
+
     function openOverlay(idx) {
         currentIdx = idx;
         /* Show before rendering — measurements (scrollWidth etc.) return 0
diff --git a/static/js/katex-bootstrap.js b/static/js/katex-bootstrap.js
new file mode 100644
index 0000000..1c553cb
--- /dev/null
+++ b/static/js/katex-bootstrap.js
@@ -0,0 +1,40 @@
+/* katex-bootstrap.js — Render every <span class="math"> / <div class="math">
+   block once KaTeX has finished loading.
+
+   Pandoc emits math blocks with the `math` class and the LaTeX source as
+   the element's text content. KaTeX is loaded with `defer` so this
+   bootstrap can simply run on DOMContentLoaded — KaTeX guarantees its
+   own definitions are available by then.
+
+   Used to live as an inline `onload="..."` attribute on the KaTeX
+   <script> tag in templates/default.html, which blocked any future
+   strict CSP. Externalized here so the entire site can run with
+   `script-src 'self'` plus a single CDN allowance.
+*/
+(function () {
+    'use strict';
+
+    function renderAll() {
+        if (typeof katex === 'undefined') return;
+        var nodes = Array.from(document.getElementsByClassName('math'));
+        nodes.forEach(function (el) {
+            if (el.tagName !== 'SPAN' && el.tagName !== 'DIV') return;
+            var src = el.textContent;
+            try {
+                katex.render(src, el, {
+                    displayMode:  el.classList.contains('display'),
+                    output:       'htmlAndMathml',
+                    throwOnError: false
+                });
+            } catch (_) {
+                /* leave the original source visible if KaTeX rejects it */
+            }
+        });
+    }
+
+    if (document.readyState === 'loading') {
+        document.addEventListener('DOMContentLoaded', renderAll);
+    } else {
+        renderAll();
+    }
+})();
diff --git a/static/js/lightbox.js b/static/js/lightbox.js
index 32f2390..0760497 100644
--- a/static/js/lightbox.js
+++ b/static/js/lightbox.js
@@ -15,7 +15,10 @@
 
         var img = document.createElement('img');
         img.className = 'lightbox-img';
-        img.alt = '';
+        /* Default accessible name; overwritten in open() with the
+           triggering image's alt when present. Avoids a nameless
+           lightbox image when the source img has no alt text. */
+        img.alt = 'Lightbox image';
 
         var caption = document.createElement('p');
         caption.className = 'lightbox-caption';
@@ -39,7 +42,10 @@
         function open(src, alt, captionText, trigger) {
             triggerEl = trigger || null;
             img.src = src;
-            img.alt = alt || '';
+            /* Prefer the source img's alt; fall back to the figure
+               caption; fall back to a generic label so the lightbox
+               image always has an accessible name. */
+            img.alt = alt || captionText || 'Lightbox image';
             caption.textContent = captionText || '';
             caption.hidden = !captionText;
             overlay.classList.add('is-open');
diff --git a/static/js/popups.js b/static/js/popups.js
index af3f3d0..ab43c84 100644
--- a/static/js/popups.js
+++ b/static/js/popups.js
@@ -99,6 +99,18 @@
         });
     }
 
+    /* Public re-init hook used by transclude.js after it injects new
+       content into the DOM. Idempotent — bind() marks each element so
+       repeated calls don't stack listeners. */
+    window.reinitPopups = function (container) {
+        if (!popup) return;          /* init() not yet run / touch device */
+        if (annotations === null) {
+            loadAnnotations().then(function () { bindTargets(container || document.body); });
+        } else {
+            bindTargets(container || document.body);
+        }
+    };
+
     /* Returns the appropriate provider function for a given URL, or null. */
     function getProvider(href) {
         if (!href) return null;
@@ -118,6 +130,11 @@
     }
 
     function bind(el, provider) {
+        /* Idempotent: skip elements that already have a popup binding,
+           so reinitPopups() called from transclude.js cannot stack
+           listeners on already-bound nodes. */
+        if (el.dataset.popupBound === '1') return;
+        el.dataset.popupBound = '1';
         el.addEventListener('mouseenter', function () { scheduleShow(el, provider); });
         el.addEventListener('mouseleave', scheduleHide);
         el.addEventListener('focus',      function () { scheduleShow(el, provider); });
@@ -133,9 +150,20 @@
         clearTimeout(showTimer);
         activeTarget = target;
         showTimer = setTimeout(function () {
-            provider(target).then(function (html) {
-                if (!html || activeTarget !== target) return;
-                popup.innerHTML = html;
+            provider(target).then(function (content) {
+                if (!content || activeTarget !== target) return;
+                /* Providers may return either an HTML string or a DOM
+                   Node — the latter is used by epistemicContent so the
+                   popup receives cloned nodes instead of a re-parsed
+                   HTML round-trip. Handle both forms. */
+                popup.innerHTML = '';
+                if (typeof content === 'string') {
+                    popup.innerHTML = content;
+                } else if (content instanceof Node) {
+                    popup.appendChild(content);
+                } else {
+                    return;
+                }
                 positionPopup(target);
                 popup.classList.add('is-visible');
                 popup.setAttribute('aria-hidden', 'false');
@@ -183,6 +211,34 @@
        Content providers
     ------------------------------------------------------------------ */
 
+    /* Cross-origin JSON fetch helper.
+       Validates Content-Type before parsing so a CORS-enabled endpoint
+       cannot return text/html and have it interpreted as JSON. The
+       caller's `.catch` still applies if the JSON parse itself fails.
+
+       Mirror helpers exist for text/* (XML/Atom) and HTML responses. */
+    function fetchJson(url, init) {
+        return fetch(url, init).then(function (r) {
+            if (!r.ok) return null;
+            var ct = (r.headers.get('content-type') || '').toLowerCase();
+            if (ct && !/(?:^|[\s;,])(?:application\/[a-z+.-]*json|text\/json)\b/.test(ct)) {
+                return null;
+            }
+            return r.json();
+        });
+    }
+
+    function fetchXml(url, init) {
+        return fetch(url, init).then(function (r) {
+            if (!r.ok) return null;
+            var ct = (r.headers.get('content-type') || '').toLowerCase();
+            if (ct && !/(?:xml|atom)/.test(ct)) {
+                return null;
+            }
+            return r.text();
+        });
+    }
+
     /* 0. Local annotations — synchronous map lookup after eager load */
     function loadAnnotations() {
         if (annotations !== null) return Promise.resolve(annotations);
@@ -288,8 +344,7 @@
             + '?action=query&prop=extracts&exintro=1&format=json&redirects=1'
             + '&titles=' + encodeURIComponent(decodeURIComponent(m[1])) + '&origin=*';
 
-        return fetch(apiUrl)
-            .then(function (r) { return r.ok ? r.json() : null; })
+        return fetchJson(apiUrl)
             .then(function (data) {
                 var pages = data && data.query && data.query.pages;
                 if (!pages) return null;
@@ -323,8 +378,7 @@
         if (!m) return Promise.resolve(null);
 
         var id = m[1].replace(/v\d+$/, '');
-        return fetch('https://export.arxiv.org/api/query?id_list=' + encodeURIComponent(id))
-            .then(function (r) { return r.ok ? r.text() : null; })
+        return fetchXml('https://export.arxiv.org/api/query?id_list=' + encodeURIComponent(id))
             .then(function (xml) {
                 if (!xml) return null;
                 var doc       = new DOMParser().parseFromString(xml, 'application/xml');
@@ -357,8 +411,7 @@
         var m = href.match(/(?:dx\.)?doi\.org\/(10\.[^?#\s]+)/);
         if (!m) return Promise.resolve(null);
 
-        return fetch('https://api.crossref.org/works/' + encodeURIComponent(m[1]))
-            .then(function (r) { return r.ok ? r.json() : null; })
+        return fetchJson('https://api.crossref.org/works/' + encodeURIComponent(m[1]))
             .then(function (data) {
                 var msg = data && data.message;
                 if (!msg) return null;
@@ -394,9 +447,8 @@
         var m = href.match(/github\.com\/([^/]+)\/([^/?#]+)/);
         if (!m) return Promise.resolve(null);
 
-        return fetch('https://api.github.com/repos/' + m[1] + '/' + m[2],
-                     { headers: { 'Accept': 'application/vnd.github.v3+json' } })
-            .then(function (r) { return r.ok ? r.json() : null; })
+        return fetchJson('https://api.github.com/repos/' + m[1] + '/' + m[2],
+                         { headers: { 'Accept': 'application/vnd.github.v3+json' } })
             .then(function (data) {
                 if (!data || !data.full_name) return null;
                 var meta = [data.language, data.stargazers_count != null ? '\u2605\u00a0' + data.stargazers_count : null]
@@ -421,8 +473,7 @@
         if (!m) return Promise.resolve(null);
 
         var apiUrl = 'https://git.levineuwirth.org/api/v1/repos/' + m[1] + '/' + m[2];
-        return fetch(apiUrl)
-            .then(function (r) { return r.ok ? r.json() : null; })
+        return fetchJson(apiUrl)
             .then(function (data) {
                 if (!data || !data.full_name) return null;
                 var meta = [data.language, data.stars_count != null ? '\u2605\u00a0' + data.stars_count : null]
@@ -446,8 +497,7 @@
         var base   = href.replace(/[?#].*$/, '');
         var apiUrl = base + '.json';
 
-        return fetch(apiUrl)
-            .then(function (r) { return r.ok ? r.json() : null; })
+        return fetchJson(apiUrl)
             .then(function (data) {
                 if (!data || !data.title) return null;
                 var desc = data.description;
@@ -476,8 +526,7 @@
         var server = /medrxiv/.test(href) ? 'medrxiv' : 'biorxiv';
         var label  = server === 'medrxiv' ? 'medRxiv' : 'bioRxiv';
 
-        return fetch('https://api.biorxiv.org/details/' + server + '/' + encodeURIComponent(doi) + '/json')
-            .then(function (r) { return r.ok ? r.json() : null; })
+        return fetchJson('https://api.biorxiv.org/details/' + server + '/' + encodeURIComponent(doi) + '/json')
             .then(function (data) {
                 var paper = data && data.collection && data.collection[0];
                 if (!paper || !paper.title) return null;
@@ -505,8 +554,7 @@
         var href = target.getAttribute('href');
         if (!href || cache[href]) return Promise.resolve(cache[href] || null);
 
-        return fetch('https://www.youtube.com/oembed?url=' + encodeURIComponent(href) + '&format=json')
-            .then(function (r) { return r.ok ? r.json() : null; })
+        return fetchJson('https://www.youtube.com/oembed?url=' + encodeURIComponent(href) + '&format=json')
             .then(function (data) {
                 if (!data || !data.title) return null;
                 return store(href,
@@ -527,8 +575,7 @@
         var m = href.match(/archive\.org\/details\/([^/?#]+)/);
         if (!m) return Promise.resolve(null);
 
-        return fetch('https://archive.org/metadata/' + encodeURIComponent(m[1]))
-            .then(function (r) { return r.ok ? r.json() : null; })
+        return fetchJson('https://archive.org/metadata/' + encodeURIComponent(m[1]))
             .then(function (data) {
                 var meta = data && data.metadata;
                 if (!meta) return null;
@@ -564,8 +611,7 @@
         var apiUrl = 'https://eutils.ncbi.nlm.nih.gov/entrez/eutils/esummary.fcgi'
                    + '?db=pubmed&id=' + pmid + '&retmode=json';
 
-        return fetch(apiUrl)
-            .then(function (r) { return r.ok ? r.json() : null; })
+        return fetchJson(apiUrl)
             .then(function (data) {
                 var paper = data && data.result && data.result[pmid];
                 if (!paper || !paper.title) return null;
@@ -597,25 +643,34 @@
 
     /* Epistemic jump link — reads the #epistemic section already in the DOM
        and renders a compact summary: status/confidence/dots + expanded DL.
-       All ep-* classes are already styled via components.css. */
+       All ep-* classes are already styled via components.css.
+
+       Returns a DocumentFragment instead of an HTML string so the popup
+       receives cloned nodes (defense in depth — if a future change ever
+       allowed user-authored HTML into the source section, the popup
+       would still see exactly the same already-rendered DOM rather than
+       a re-parsed string). */
     function epistemicContent() {
         var section = document.getElementById('epistemic');
         if (!section) return Promise.resolve(null);
 
-        var html = '<div class="popup-epistemic">';
+        var wrap = document.createElement('div');
+        wrap.className = 'popup-epistemic';
 
         var compact = section.querySelector('.ep-compact');
         if (compact) {
-            html += '<div class="ep-compact">' + compact.innerHTML + '</div>';
+            var compactClone = compact.cloneNode(true);
+            wrap.appendChild(compactClone);
         }
 
         var expanded = section.querySelector('.ep-expanded');
         if (expanded) {
-            html += '<dl class="ep-expanded">' + expanded.innerHTML + '</dl>';
+            var expandedClone = expanded.cloneNode(true);
+            wrap.appendChild(expandedClone);
         }
 
-        html += '</div>';
-        return Promise.resolve(html || null);
+        if (!compact && !expanded) return Promise.resolve(null);
+        return Promise.resolve(wrap);
     }
 
     /* Local PDF — shows the build-time first-page thumbnail (.thumb.png).
@@ -652,12 +707,11 @@
             });
     }
 
+    /* Defer to the shared utility (loaded synchronously from
+       templates/partials/head.html) so this file cannot drift from
+       annotations.js, semantic-search.js, or build/Utils.hs. */
     function esc(s) {
-        return String(s)
-            .replace(/&/g, '&amp;')
-            .replace(/</g, '&lt;')
-            .replace(/>/g, '&gt;')
-            .replace(/"/g, '&quot;');
+        return window.lnUtils.escapeHtml(s);
     }
 
     /* Emit a .popup-source label with a data-popup-source attribute so CSS
diff --git a/static/js/semantic-search.js b/static/js/semantic-search.js
index 823562d..78a9db1 100644
--- a/static/js/semantic-search.js
+++ b/static/js/semantic-search.js
@@ -62,10 +62,17 @@
        Model loading — dynamic import from CDN, lazy
     ------------------------------------------------------------------ */
 
+    /* In-flight promise so concurrent searches share a single model
+       load. Without this guard, two rapid keystrokes would each call
+       `import(CDN)` and `pipeline(...)`, wasting CPU and memory before
+       the second resolves. */
+    var loadModelPromise = null;
+
     function loadModel() {
         if (extractor) return Promise.resolve(extractor);
+        if (loadModelPromise) return loadModelPromise;
         setStatus('Loading model…');
-        return import(CDN).then(function (mod) {
+        loadModelPromise = import(CDN).then(function (mod) {
             /* Point transformers.js at our self-hosted model files. */
             mod.env.localModelPath   = MODEL_PATH;
             mod.env.allowRemoteModels = false;
@@ -73,7 +80,13 @@
         }).then(function (pipe) {
             extractor = pipe;
             return extractor;
+        }).catch(function (err) {
+            /* Allow a retry on the next call instead of caching the
+               failed promise forever. */
+            loadModelPromise = null;
+            throw err;
         });
+        return loadModelPromise;
     }
 
     /* ------------------------------------------------------------------
@@ -163,12 +176,11 @@
         statusEl.textContent = msg;
     }
 
+    /* Defer to the shared utility (loaded synchronously from
+       templates/partials/head.html) so this file cannot drift from
+       popups.js, annotations.js, or build/Utils.hs. */
     function esc(s) {
-        return String(s)
-            .replace(/&/g, '&amp;')
-            .replace(/</g, '&lt;')
-            .replace(/>/g, '&gt;')
-            .replace(/"/g, '&quot;');
+        return window.lnUtils.escapeHtml(s);
     }
 
     /* ------------------------------------------------------------------
diff --git a/static/js/settings.js b/static/js/settings.js
index 7e31dc1..5510d62 100644
--- a/static/js/settings.js
+++ b/static/js/settings.js
@@ -1,11 +1,19 @@
 /* settings.js — Settings panel: theme, text size, print.
-   Must stay in sync with TEXT_SIZES in theme.js. */
+   Must stay in sync with TEXT_SIZES in theme.js.
+
+   All localStorage access routes through window.lnUtils.safeStorage so
+   Safari private-mode SecurityErrors on writes do not throw uncaught. */
 (function () {
     'use strict';
 
     var TEXT_SIZES    = [20, 23, 26];
     var TEXT_SIZE_DEFAULT = 1;      /* index of 23px */
     var TEXT_SIZE_KEY = 'text-size';
+    var store = (window.lnUtils && window.lnUtils.safeStorage) || {
+        get: function () { return null; },
+        set: function () { return false; },
+        remove: function () { return false; }
+    };
 
     /* ------------------------------------------------------------------
        Init
@@ -102,7 +110,7 @@
 
     function setTheme(theme) {
         document.documentElement.setAttribute('data-theme', theme);
-        localStorage.setItem('theme', theme);
+        store.set('theme', theme);
         syncThemeButtons();
     }
 
@@ -122,13 +130,13 @@
     /* Text size ------------------------------------------------------- */
 
     function getSizeIndex() {
-        var n = parseInt(localStorage.getItem(TEXT_SIZE_KEY), 10);
+        var n = parseInt(store.get(TEXT_SIZE_KEY), 10);
         return (isNaN(n) || n < 0 || n >= TEXT_SIZES.length) ? TEXT_SIZE_DEFAULT : n;
     }
 
     function shiftSize(delta) {
         var idx = Math.max(0, Math.min(TEXT_SIZES.length - 1, getSizeIndex() + delta));
-        localStorage.setItem(TEXT_SIZE_KEY, idx);
+        store.set(TEXT_SIZE_KEY, idx);
         document.documentElement.style.setProperty('--text-size', TEXT_SIZES[idx] + 'px');
         syncTextSizeButtons();
     }
@@ -140,10 +148,10 @@
         var on   = html.hasAttribute(attrName);
         if (on) {
             html.removeAttribute(attrName);
-            localStorage.removeItem(storageKey);
+            store.remove(storageKey);
         } else {
             html.setAttribute(attrName, '');
-            localStorage.setItem(storageKey, '1');
+            store.set(storageKey, '1');
         }
         syncToggleButton(storageKey, attrName);
     }
diff --git a/static/js/sidenotes.js b/static/js/sidenotes.js
index e038a63..656afe2 100644
--- a/static/js/sidenotes.js
+++ b/static/js/sidenotes.js
@@ -52,13 +52,19 @@
     }
 
     /* ------------------------------------------------------------------ */
-    /*  Hover + click wiring                                               */
+    /*  Hover + click + keyboard wiring                                    */
     /* ------------------------------------------------------------------ */
 
     /* At most one sidenote is "focused" (click-sticky) at a time. */
     let focusedPair = null;
 
     function wireHover(ref, sn) {
+        /* Idempotent: skip pairs already wired so 'reinitSidenotes'
+           after a transclusion injection cannot stack listeners. */
+        if (ref.dataset.snBound === '1') return;
+        ref.dataset.snBound = '1';
+        sn.dataset.snBound  = '1';
+
         let hovering = false;
         let focused  = false;
 
@@ -70,6 +76,22 @@
 
         function unfocus() { focused = false; update(); }
 
+        function toggleFocus() {
+            /* Sticky focus only makes sense on wide viewports where the
+               sidenote is actually visible. On narrow screens there's
+               nothing to pin. */
+            if (getComputedStyle(sn).display === 'none') return;
+            if (focused) {
+                focused = false;
+                focusedPair = null;
+            } else {
+                if (focusedPair) focusedPair.unfocus();
+                focused = true;
+                focusedPair = { ref: ref, sn: sn, unfocus: unfocus };
+            }
+            update();
+        }
+
         ref.addEventListener('mouseenter', function () { hovering = true;  update(); });
         ref.addEventListener('mouseleave', function () { hovering = false; update(); });
         sn.addEventListener('mouseenter',  function () { hovering = true;  update(); });
@@ -81,16 +103,25 @@
         if (link) {
             link.addEventListener('click', function (e) {
                 e.preventDefault();
-                if (getComputedStyle(sn).display === 'none') return; /* narrow: no sidenote to focus */
-                if (focused) {
+                toggleFocus();
+            });
+
+            /* Keyboard activation: Enter follows the link by default (the
+               browser synthesizes a click), but Space does not. Both are
+               expected to toggle focus on a focus-activated element, so
+               we normalize: Enter/Space toggle, Escape clears if focused.
+               The <a href="#sn-N"> retains its native focusability so
+               Tab reaches it; we only intercept the key. */
+            link.addEventListener('keydown', function (e) {
+                if (e.key === ' ') {
+                    e.preventDefault();
+                    toggleFocus();
+                } else if (e.key === 'Escape' && focused) {
+                    e.preventDefault();
                     focused = false;
                     focusedPair = null;
-                } else {
-                    if (focusedPair) focusedPair.unfocus();
-                    focused = true;
-                    focusedPair = { ref: ref, sn: sn, unfocus: unfocus };
+                    update();
                 }
-                update();
             });
         }
     }
@@ -105,19 +136,39 @@
         }
     });
 
-    function init() {
-        const body = document.getElementById('markdownBody');
-        if (!body) return;
+    /* Global Escape dismisses any sticky-focused sidenote, even if focus
+       has moved away from the ref link. */
+    document.addEventListener('keydown', function (e) {
+        if (e.key === 'Escape' && focusedPair) {
+            focusedPair.unfocus();
+            focusedPair = null;
+        }
+    });
 
-        body.querySelectorAll('.sidenote').forEach(function (sn) {
+    function wireAll(root) {
+        root.querySelectorAll('.sidenote').forEach(function (sn) {
             const refId = 'snref-' + sn.id.slice(3);
             const ref   = document.getElementById(refId);
             if (ref) wireHover(ref, sn);
         });
+    }
 
+    function init() {
+        const body = document.getElementById('markdownBody');
+        if (!body) return;
+
+        wireAll(body);
         positionSidenotes();
     }
 
+    /* Public re-init hook used by transclude.js after it injects new
+       content. wireAll is idempotent so calling this multiple times is
+       safe. */
+    window.reinitSidenotes = function (container) {
+        wireAll(container || document.getElementById('markdownBody') || document);
+        positionSidenotes();
+    };
+
     document.addEventListener('DOMContentLoaded', init);
     window.addEventListener('resize', positionSidenotes);
 }());
diff --git a/static/js/theme.js b/static/js/theme.js
index 09304c7..b7037bb 100644
--- a/static/js/theme.js
+++ b/static/js/theme.js
@@ -1,29 +1,36 @@
 /* theme.js — Restores theme and text size from localStorage before first paint.
    Loaded synchronously (no defer/async) to prevent flash of wrong appearance.
    DOM interaction (button wiring) is handled by settings.js (deferred).
+
+   All storage access routes through window.lnUtils.safeStorage (from
+   utils.js, loaded immediately before this script) so Safari private-mode
+   SecurityErrors degrade to default appearance rather than blowing up
+   the synchronous bootstrap.
 */
 (function () {
     var TEXT_SIZES = [20, 23, 26];
+    var store = window.lnUtils && window.lnUtils.safeStorage;
+    function safeGet(key) { return store ? store.get(key) : null; }
 
     /* Theme */
-    var storedTheme = localStorage.getItem('theme');
+    var storedTheme = safeGet('theme');
     if (storedTheme === 'dark' || storedTheme === 'light') {
         document.documentElement.setAttribute('data-theme', storedTheme);
     }
 
     /* Text size */
-    var storedSize = parseInt(localStorage.getItem('text-size'), 10);
+    var storedSize = parseInt(safeGet('text-size'), 10);
     if (!isNaN(storedSize) && storedSize >= 0 && storedSize < TEXT_SIZES.length) {
         document.documentElement.style.setProperty('--text-size', TEXT_SIZES[storedSize] + 'px');
     }
 
     /* Focus mode */
-    if (localStorage.getItem('focus-mode')) {
+    if (safeGet('focus-mode')) {
         document.documentElement.setAttribute('data-focus-mode', '');
     }
 
     /* Reduce motion */
-    if (localStorage.getItem('reduce-motion')) {
+    if (safeGet('reduce-motion')) {
         document.documentElement.setAttribute('data-reduce-motion', '');
     }
 })();
diff --git a/static/js/toc.js b/static/js/toc.js
index 2e732e4..91ae54f 100644
--- a/static/js/toc.js
+++ b/static/js/toc.js
@@ -39,11 +39,26 @@
             }
         }
 
-        // Collapse / expand
+        // Collapse / expand. The collapsed state is hidden from
+        // assistive technology (aria-hidden="true") and removed from
+        // the keyboard tab order (tabindex=-1 on each link), so users
+        // navigating with a screen reader or only the keyboard cannot
+        // land on links inside a collapsed TOC.
+        const tocNav = toc.querySelector('.toc-nav');
         function setExpanded(open) {
             if (!toggleBtn) return;
             toc.classList.toggle('is-collapsed', !open);
             toggleBtn.setAttribute('aria-expanded', String(open));
+            if (tocNav) {
+                tocNav.setAttribute('aria-hidden', String(!open));
+            }
+            links.forEach(function (a) {
+                if (open) {
+                    a.removeAttribute('tabindex');
+                } else {
+                    a.setAttribute('tabindex', '-1');
+                }
+            });
         }
 
         setExpanded(true);
@@ -54,13 +69,6 @@
             });
         }
 
-        // Auto-collapse once the first section becomes active via scrolling.
-        let autoCollapsed = false;
-        function collapseOnce() {
-            if (autoCollapsed) return;
-            autoCollapsed = true;
-            setExpanded(false);
-        }
 
         // Progress indicator — drives the horizontal bar under .toc-header.
         function updateProgress() {
@@ -83,7 +91,7 @@
             if (visible.size > 0) {
                 // Activate the topmost visible heading in document order.
                 const top = headings.find(h => visible.has(h));
-                if (top) { activate(top.id); collapseOnce(); }
+                if (top) { activate(top.id); }
             } else {
                 // Nothing in the trigger band: activate the last heading
                 // whose top edge is above the sticky nav bar.
@@ -93,7 +101,7 @@
                     if (h.getBoundingClientRect().top < navHeight + 16) candidate = h;
                     else break;
                 }
-                if (candidate) { activate(candidate.id); collapseOnce(); }
+                if (candidate) { activate(candidate.id); }
                 else activateTitle();
             }
         }, {
diff --git a/static/js/transclude.js b/static/js/transclude.js
index b9f0b7f..8aa4882 100644
--- a/static/js/transclude.js
+++ b/static/js/transclude.js
@@ -81,8 +81,21 @@
 
     /* After injection, retrigger layout-dependent subsystems. */
     function reinitFragment(container) {
-        /* sidenotes.js repositions on resize — dispatch to trigger it. */
-        window.dispatchEvent(new Event('resize'));
+        /* sidenotes.js — wire newly injected sidenote refs/spans and
+           reposition the column. Falls back to a manual resize event
+           for older builds that haven't been redeployed yet. */
+        if (typeof window.reinitSidenotes === 'function') {
+            window.reinitSidenotes(container);
+        } else {
+            window.dispatchEvent(new Event('resize'));
+        }
+
+        /* popups.js — bind hover popups for newly injected links so
+           transcluded content has the same preview behaviour as the
+           host page. */
+        if (typeof window.reinitPopups === 'function') {
+            window.reinitPopups(container);
+        }
 
         /* collapse.js exposes reinitCollapse for newly added headings. */
         if (typeof window.reinitCollapse === 'function') {
diff --git a/static/js/utils.js b/static/js/utils.js
new file mode 100644
index 0000000..b55c052
--- /dev/null
+++ b/static/js/utils.js
@@ -0,0 +1,48 @@
+/* utils.js — Tiny shared helpers loaded before any other script.
+   Loaded synchronously (no `defer`) from templates/partials/head.html so
+   that defer'd scripts can rely on `window.lnUtils` existing at run time.
+
+   Keep this file dependency-free and minimal. It's the lowest-level
+   layer in the JS stack — anything heavier should live in a feature
+   module instead. */
+(function (global) {
+    'use strict';
+
+    var lnUtils = global.lnUtils || {};
+
+    /* Escape a string for safe interpolation into HTML text content or
+       double-quoted attribute values. The order of replacements matters:
+       `&` MUST come first, otherwise the `&amp;` injected by other rules
+       gets re-escaped to `&amp;amp;`.
+
+       Mirror of `Utils.escapeHtml` in build/Utils.hs. */
+    lnUtils.escapeHtml = function (s) {
+        return String(s)
+            .replace(/&/g,  '&amp;')
+            .replace(/</g,  '&lt;')
+            .replace(/>/g,  '&gt;')
+            .replace(/"/g,  '&quot;')
+            .replace(/'/g,  '&#39;');
+    };
+
+    /* Safe localStorage wrapper. Safari throws SecurityError in private
+       browsing mode on every access — including writes — so reads AND
+       writes need to be guarded. Every consumer that touches storage
+       should route through this helper so degradation is uniform. */
+    lnUtils.safeStorage = {
+        get: function (key) {
+            try { return localStorage.getItem(key); }
+            catch (_) { return null; }
+        },
+        set: function (key, value) {
+            try { localStorage.setItem(key, value); return true; }
+            catch (_) { return false; }
+        },
+        remove: function (key) {
+            try { localStorage.removeItem(key); return true; }
+            catch (_) { return false; }
+        }
+    };
+
+    global.lnUtils = lnUtils;
+})(window);
diff --git a/templates/default.html b/templates/default.html
index 599146c..28e4068 100644
--- a/templates/default.html
+++ b/templates/default.html
@@ -28,8 +28,8 @@ $if(home)$<script src="/js/random.js" defer></script>$endif$
 $if(reading)$<script src="/js/reading.js" defer></script>$endif$
 $for(page-scripts)$<script src="/$script-src$" defer></script>$endfor$
 $if(math)$
-<script defer src="https://cdn.jsdelivr.net/npm/katex@0.16.11/dist/katex.min.js"
-    onload="(function(){var els=Array.from(document.getElementsByClassName('math'));els.forEach(function(el){if(el.tagName==='SPAN'){var src=el.textContent;katex.render(src,el,{displayMode:el.classList.contains('display'),output:'htmlAndMathml',throwOnError:false})}})})()"></script>
+<script defer src="https://cdn.jsdelivr.net/npm/katex@0.16.11/dist/katex.min.js"></script>
+<script defer src="/js/katex-bootstrap.js"></script>
 $endif$
 </body>
 </html>
diff --git a/templates/partials/head.html b/templates/partials/head.html
index 6c70520..0e7e7a3 100644
--- a/templates/partials/head.html
+++ b/templates/partials/head.html
@@ -28,6 +28,7 @@ $endif$
 $if(search)$
 <link rel="stylesheet" href="/pagefind/pagefind-ui.css">
 $endif$
+<script src="/js/utils.js"></script>
 <script src="/js/theme.js"></script>
 $if(viz)$
 <link rel="stylesheet" href="/css/viz.css">
diff --git a/templates/partials/nav.html b/templates/partials/nav.html
index 97ceb6e..969de60 100644
--- a/templates/partials/nav.html
+++ b/templates/partials/nav.html
@@ -12,36 +12,36 @@
                 <a href="/search.html">Search</a>
             </div>
             <div class="nav-controls">
-                <button class="nav-portal-toggle" aria-label="Toggle portals" aria-expanded="false">
+                <button type="button" class="nav-portal-toggle" aria-label="Toggle portals" aria-expanded="false">
                     <span class="nav-portal-arrow">▼</span>Portals
                 </button>
                 <div class="settings-wrap">
-                    <button class="settings-toggle" aria-label="Open settings" aria-expanded="false">⚙</button>
+                    <button type="button" class="settings-toggle" aria-label="Open settings" aria-expanded="false">⚙</button>
                     <div class="settings-panel" aria-hidden="true">
                         <div class="settings-section">
                             <div class="settings-label">Theme</div>
                             <div class="settings-row">
-                                <button class="settings-btn" data-action="theme-light">Light</button>
-                                <button class="settings-btn" data-action="theme-dark">Dark</button>
+                                <button type="button" class="settings-btn" data-action="theme-light">Light</button>
+                                <button type="button" class="settings-btn" data-action="theme-dark">Dark</button>
                             </div>
                         </div>
                         <div class="settings-section">
                             <div class="settings-label">Text size</div>
                             <div class="settings-row">
-                                <button class="settings-btn" data-action="text-smaller" aria-label="Decrease text size">A−</button>
-                                <button class="settings-btn" data-action="text-larger"  aria-label="Increase text size">A+</button>
+                                <button type="button" class="settings-btn" data-action="text-smaller" aria-label="Decrease text size">A−</button>
+                                <button type="button" class="settings-btn" data-action="text-larger"  aria-label="Increase text size">A+</button>
                             </div>
                         </div>
                         <div class="settings-section">
                             <div class="settings-label">Display</div>
                             <div class="settings-col">
-                                <button class="settings-btn settings-btn--full" data-action="focus-mode">Focus Mode</button>
-                                <button class="settings-btn settings-btn--full" data-action="reduce-motion">Reduce Motion</button>
+                                <button type="button" class="settings-btn settings-btn--full" data-action="focus-mode">Focus Mode</button>
+                                <button type="button" class="settings-btn settings-btn--full" data-action="reduce-motion">Reduce Motion</button>
                             </div>
                         </div>
                         <div class="settings-section">
-                            <button class="settings-btn settings-btn--full" data-action="print">Print</button>
-                            <button class="settings-btn settings-btn--full settings-btn--danger" data-action="clear-annotations">Clear Annotations</button>
+                            <button type="button" class="settings-btn settings-btn--full" data-action="print">Print</button>
+                            <button type="button" class="settings-btn settings-btn--full settings-btn--danger" data-action="clear-annotations">Clear Annotations</button>
                         </div>
                     </div>
                 </div>