Fix clipboard fallback selection inside dialogs (#433)

public/js/ui/clipboard.js

@@ -1,35 +1,32 @@
-// Clipboard helper shared by the room screen (invite code / link) and 干员调配 (导出 / 导入 payloads).
-//
-// Lives here rather than in a screen: `screens/room.js` imports `screens/loadout.js` (the 干员调配 button), so loadout
-// importing the helper back from room would be a cycle.
-
-/**
- * Copy text to the clipboard (async API with a textarea fallback for insecure contexts).
- * @param {string} text
- * @returns {Promise<boolean>}
- */
+// Shared by invite links, loadouts and settings exports, including LAN / insecure contexts.
+/** @param {string} text @returns {Promise<boolean>} */
 export async function copyText(text) {
   try {
     if (globalThis.navigator?.clipboard && globalThis.isSecureContext) {
       await navigator.clipboard.writeText(text);
       return true;
     }
-  } catch { /* fall through */ }
+  } catch { /* use the selected-text fallback */ }
+  let ta, prev;
   try {
-    const ta = document.createElement('textarea');
+    prev = document.activeElement;
+    ta = document.createElement('textarea');
     ta.value = text;
     ta.setAttribute('readonly', '');
-    // 16 px: iOS zooms into smaller focused fields; `readonly` keeps the keyboard away
+    // Keep the temporary selection inside the active focus trap (#433). The 16 px readonly field avoids iOS zoom
+    // and its keyboard; do not disable the dialog's focus protection or copy a selection redirected to another field.
     ta.style.cssText = 'position:fixed;left:-9999px;top:0;opacity:0;font-size:16px';
-    document.body.appendChild(ta);
+    const host = prev?.closest?.('[role="dialog"][aria-modal="true"], .guide') || document.body;
+    host.appendChild(ta);
+    ta.focus({ preventScroll: true });
     ta.select();
-    // iOS Safari ignores select() on a textarea: an explicit range is what it copies (LAN play over http has no
-    // navigator.clipboard, so this path is the one iPhones / iPads take)
-    try { ta.setSelectionRange(0, ta.value.length); } catch { /* ignore */ }
-    const ok = document.execCommand('copy');
-    ta.remove();
-    return ok;
+    ta.setSelectionRange(0, ta.value.length); // iOS Safari ignores select() alone
+    if (document.activeElement !== ta || ta.selectionStart !== 0 || ta.selectionEnd !== ta.value.length) return false;
+    return !!document.execCommand('copy');
   } catch {
     return false;
+  } finally {
+    ta?.remove();
+    if (prev?.isConnected) prev.focus?.({ preventScroll: true });
   }
 }