Fix WebCRT copy/paste on HTTP LAN by falling back off Clipboard API.

Co-authored-by: Cursor <cursoragent@cursor.com>

web/src/utils/clipboard.ts

@@ -0,0 +1,65 @@
+/** Clipboard helpers that work on http://LAN (non-secure) as well as HTTPS. */
+
+export function isClipboardApiAvailable(): boolean {
+  try {
+    return Boolean(
+      typeof window !== "undefined" &&
+        window.isSecureContext &&
+        navigator.clipboard &&
+        typeof navigator.clipboard.writeText === "function",
+    );
+  } catch {
+    return false;
+  }
+}
+
+/** Write text; prefers Clipboard API, falls back to execCommand('copy'). */
+export async function writeClipboardText(text: string): Promise<boolean> {
+  const value = String(text || "");
+  if (!value) return false;
+
+  if (isClipboardApiAvailable() && navigator.clipboard?.writeText) {
+    try {
+      await navigator.clipboard.writeText(value);
+      return true;
+    } catch {
+      /* fall through */
+    }
+  }
+
+  try {
+    const ta = document.createElement("textarea");
+    ta.value = value;
+    ta.setAttribute("readonly", "");
+    ta.style.cssText = "position:fixed;left:-9999px;top:0;opacity:0";
+    document.body.appendChild(ta);
+    ta.focus();
+    ta.select();
+    ta.setSelectionRange(0, value.length);
+    const ok = document.execCommand("copy");
+    document.body.removeChild(ta);
+    return Boolean(ok);
+  } catch {
+    return false;
+  }
+}
+
+/**
+ * Read clipboard via Clipboard API when available.
+ * On insecure http://IP, returns null — caller must use a paste-event bridge.
+ */
+export async function readClipboardText(): Promise<string | null> {
+  if (
+    typeof window !== "undefined" &&
+    window.isSecureContext &&
+    navigator.clipboard &&
+    typeof navigator.clipboard.readText === "function"
+  ) {
+    try {
+      return await navigator.clipboard.readText();
+    } catch {
+      return null;
+    }
+  }
+  return null;
+}