feat: scroll-position memory on repertoire HTMX swaps + swap transition polish

- Add repertoire-scroll-restore.js: snapshots scrollTop of each column <ul>
  before htmx:beforeSwap, restores after htmx:afterSwap (keyed by data-col)
- Add subtle opacity transition on #repertoire-index during htmx-swapping
- Tighten rep-indicator opacity transition to 0.1s for snappier feedback
- Import new module in public-entry.js

TODO.md

@@ -3,6 +3,13 @@
 > Last updated: 2026-06-24
 > Context: Security audit — fix open redirects, fragment auth, dead code, CSRF gaps
 
+## Deferred / Blocked
+- [ ] #tighten-csp Tighten CSP to remove 'unsafe-inline' after inline JS extraction
+
+## Pending
+- [ ] #rep-student-touch Replace hover student popover with tap-to-open drawer for mobile `(repertoire.php, repertoire.css, repertoire-student-popover.js)`
+- [x] #rep-polish Polish: scroll-position memory on HTMX swap, animation tuning `(repertoire.css)` ✓
+
 ## Completed
 - [x] #icon-color-verify Verify icon colors render correctly across all pages (header, admin tables, forms, dialogs, cleanup modal) ✓
 - [x] #sec-open-redirect Fix open redirect in tag.php + language.php (protocol-relative URL bypass via str_starts_with) ✓
@@ -18,12 +25,6 @@
 - [x] #sec-fragments-auth Gate partagé fragments on share_active session (read-only fragment renderers — no CSRF needed) ✓
 - [x] #sec-retry-csrf Add CSRF check to partage/retry-email.php POST ✓
 - [x] #sec-cleanup-dead-code Remove dead App::verifyCsrf() or refactor action handlers to use it ✓
-
-## Pending
-- [ ] #rep-student-touch Replace hover student popover with tap-to-open drawer for mobile `(repertoire.php, repertoire.css, repertoire-student-popover.js)`
-- [ ] #rep-polish Polish: scroll-position memory on HTMX swap, animation tuning `(repertoire.css)`
-
-## Completed (before this session)
 - [x] #gzip-nginx Enable gzip compression in nginx config `(nginx/xamxam.conf)` ✓
 - [x] #extract-inline-js Move inline JS to external files across 17 templates → 15 new JS files created `(app/public/assets/js/app/*.js)` ✓
 - [x] #inline-icon-helper Create `icon()` PHP helper + auto-load in bootstrap `(src/icon.php, bootstrap.php)` ✓
@@ -77,5 +78,3 @@
 - [x] #split-form-css Split `form.css` into `form-base.css` and `form-admin.css` ✓
 - [x] #extra-css-admin Update `head.php` to support `$extraCssAdmin` for admin-only stylesheets `(head.php)` ✓
 
-## Deferred / Blocked
-- [ ] #tighten-csp Tighten CSP to remove 'unsafe-inline' after inline JS extraction

app/public/assets/css/repertoire.css

@@ -290,6 +290,17 @@
     color: var(--accent-primary);
 }
 
+/* ── Swap transition ────────────────────────────────────────────────── */
+
+.repertoire-index.htmx-swapping {
+    opacity: 0.5;
+    transition: opacity 0.1s ease-out;
+}
+
+.repertoire-index {
+    transition: opacity 0.15s ease-in;
+}
+
 /* Link variant (students col) — no underline by default */
 .rep-entry--link {
     text-decoration: none;
@@ -333,7 +344,7 @@
     height: 2px;
     background: var(--accent-primary);
     opacity: 0;
-    transition: opacity 0.15s;
+    transition: opacity 0.1s;
     z-index: 100;
     pointer-events: none;
 }

app/public/assets/js/app/public-entry.js

@@ -14,6 +14,7 @@ import "./htmx-global-setup.js";
 
 // Public page features
 import "./repertoire-accordion.js";
+import "./repertoire-scroll-restore.js";
 import "./repertoire-student-popover.js";
 import "./access-request.js";
 import "./acces-password.js";

app/public/assets/js/app/repertoire-scroll-restore.js

@@ -0,0 +1,70 @@
+/**
+ * repertoire-scroll-restore.js — Preserve column scroll positions on HTMX swap.
+ *
+ * When a filter button triggers an HTMX swap that replaces #repertoire-index,
+ * the new markup replaces the old, resetting all column scroll positions to 0.
+ * This module captures scrollTop of each scrollable <ul> before the swap and
+ * restores it after, keyed by data-col attribute so the mapping survives
+ * DOM replacement.
+ */
+(() => {
+    var INDEX_SEL = '#repertoire-index';
+    var scrollSnapshots = {};
+
+    function snapshot() {
+        var index = document.querySelector(INDEX_SEL);
+        if (!index) return;
+        scrollSnapshots = {};
+        index.querySelectorAll('.repertoire-col[data-col] > ul').forEach((ul) => {
+            var col = ul.closest('.repertoire-col');
+            if (!col) return;
+            var key = col.getAttribute('data-col');
+            scrollSnapshots[key] = ul.scrollTop;
+        });
+    }
+
+    function restore() {
+        var index = document.querySelector(INDEX_SEL);
+        if (!index) return;
+        index.querySelectorAll('.repertoire-col[data-col] > ul').forEach((ul) => {
+            var col = ul.closest('.repertoire-col');
+            if (!col) return;
+            var key = col.getAttribute('data-col');
+            if (scrollSnapshots[key] !== undefined) {
+                ul.scrollTop = scrollSnapshots[key];
+            }
+        });
+    }
+
+    // Capture scroll positions before the outgoing element is replaced
+    document.body.addEventListener('htmx:beforeSwap', (e) => {
+        if (
+            e.detail.target &&
+            e.detail.target.matches &&
+            e.detail.target.matches(INDEX_SEL)
+        ) {
+            snapshot();
+        }
+    });
+
+    // Restore after the new content is in the DOM
+    document.body.addEventListener('htmx:afterSwap', (e) => {
+        if (
+            e.detail.target &&
+            e.detail.target.matches &&
+            e.detail.target.matches(INDEX_SEL)
+        ) {
+            // Use requestAnimationFrame to ensure layout has settled
+            requestAnimationFrame(() => {
+                restore();
+            });
+        }
+    });
+
+    // Also restore on history navigation (browser back/forward)
+    document.body.addEventListener('htmx:historyRestore', () => {
+        requestAnimationFrame(() => {
+            restore();
+        });
+    });
+})();