fix(app): handle multiline web paste in prompt composer (#17509)

packages/app/src/components/prompt-input/paste.ts

@@ -0,0 +1,24 @@
+const LARGE_PASTE_CHARS = 8000
+const LARGE_PASTE_BREAKS = 120
+
+function largePaste(text: string) {
+  if (text.length >= LARGE_PASTE_CHARS) return true
+  let breaks = 0
+  for (const char of text) {
+    if (char !== "\n") continue
+    breaks += 1
+    if (breaks >= LARGE_PASTE_BREAKS) return true
+  }
+  return false
+}
+
+export function normalizePaste(text: string) {
+  if (!text.includes("\r")) return text
+  return text.replace(/\r\n?/g, "\n")
+}
+
+export function pasteMode(text: string) {
+  if (largePaste(text)) return "manual"
+  if (text.includes("\n") || text.includes("\r")) return "manual"
+  return "native"
+}