fix: add keyboard focus trap to crisis overlay (#80)

Merge PR #80 (squash)

index.html

@@ -983,12 +983,60 @@ Sovereignty and service always.`;
 
 
   // ===== OVERLAY =====
+
+  // Focus trap: cycle through focusable elements within the crisis overlay
+  function getOverlayFocusableElements() {
+    return crisisOverlay.querySelectorAll(
+      'a[href], button:not([disabled]), [tabindex]:not([tabindex="-1"])'
+    );
+  }
+
+  function trapFocusInOverlay(e) {
+    if (!crisisOverlay.classList.contains('active')) return;
+    if (e.key !== 'Tab') return;
+
+    var focusable = getOverlayFocusableElements();
+    if (focusable.length === 0) return;
+
+    var first = focusable[0];
+    var last = focusable[focusable.length - 1];
+
+    if (e.shiftKey) {
+      // Shift+Tab: if on first, wrap to last
+      if (document.activeElement === first) {
+        e.preventDefault();
+        last.focus();
+      }
+    } else {
+      // Tab: if on last, wrap to first
+      if (document.activeElement === last) {
+        e.preventDefault();
+        first.focus();
+      }
+    }
+  }
+
+  // Store the element that had focus before the overlay opened
+  var _preOverlayFocusElement = null;
+
   function showOverlay() {
+    // Save current focus for restoration on dismiss
+    _preOverlayFocusElement = document.activeElement;
+
     crisisOverlay.classList.add('active');
     overlayDismissBtn.disabled = true;
     var countdown = 10;
     overlayDismissBtn.textContent = 'Continue to chat (' + countdown + 's)';
 
+    // Disable background interaction via inert attribute
+    var mainApp = document.querySelector('.app');
+    if (mainApp) mainApp.setAttribute('inert', '');
+    // Also hide from assistive tech
+    var chatSection = document.getElementById('chat');
+    if (chatSection) chatSection.setAttribute('aria-hidden', 'true');
+    var footerEl = document.querySelector('footer');
+    if (footerEl) footerEl.setAttribute('aria-hidden', 'true');
+
     if (overlayTimer) clearInterval(overlayTimer);
     overlayTimer = setInterval(function() {
       countdown--;
@@ -1005,6 +1053,9 @@ Sovereignty and service always.`;
     overlayDismissBtn.focus();
   }
 
+  // Register focus trap on document (always listening, gated by class check)
+  document.addEventListener('keydown', trapFocusInOverlay);
+
   overlayDismissBtn.addEventListener('click', function() {
     if (!overlayDismissBtn.disabled) {
       crisisOverlay.classList.remove('active');
@@ -1012,7 +1063,22 @@ Sovereignty and service always.`;
         clearInterval(overlayTimer);
         overlayTimer = null;
       }
-      msgInput.focus();
+
+      // Re-enable background interaction
+      var mainApp = document.querySelector('.app');
+      if (mainApp) mainApp.removeAttribute('inert');
+      var chatSection = document.getElementById('chat');
+      if (chatSection) chatSection.removeAttribute('aria-hidden');
+      var footerEl = document.querySelector('footer');
+      if (footerEl) footerEl.removeAttribute('aria-hidden');
+
+      // Restore focus to the element that had it before the overlay opened
+      if (_preOverlayFocusElement && typeof _preOverlayFocusElement.focus === 'function') {
+        _preOverlayFocusElement.focus();
+      } else {
+        msgInput.focus();
+      }
+      _preOverlayFocusElement = null;
     }
   });