feat(input): drag-drop + paste-as-attachment for long text

apps/web/src/lib/attachments.ts

@@ -8,6 +8,34 @@ export type Attachment = {
   source: '@' | 'line-select' | 'drop' | 'paste';
 };
 
+// v1.7: caps shared between drag-drop and paste-as-attachment so both paths
+// reject the same way. Match the existing 10-attachment cap in
+// ChatInput.addAttachment.
+export const MAX_FILE_SIZE_BYTES = 5 * 1024 * 1024; // 5 MB
+export const PASTE_INLINE_MAX_LINES = 8;
+
+// First-8KB null-byte scan. Returns true if the content looks binary.
+// Accepts a string (post-decode), an ArrayBuffer (pre-decode), or a Uint8Array.
+// For binary files like PNG, scanning bytes is more reliable than scanning
+// post-UTF-8-decode strings because invalid sequences may be replaced rather
+// than preserved.
+export function looksBinary(content: string | ArrayBuffer | Uint8Array): boolean {
+  const SCAN_BYTES = 8192;
+  if (typeof content === 'string') {
+    const max = Math.min(content.length, SCAN_BYTES);
+    for (let i = 0; i < max; i++) {
+      if (content.charCodeAt(i) === 0) return true;
+    }
+    return false;
+  }
+  const bytes = content instanceof Uint8Array ? content : new Uint8Array(content);
+  const max = Math.min(bytes.length, SCAN_BYTES);
+  for (let i = 0; i < max; i++) {
+    if (bytes[i] === 0) return true;
+  }
+  return false;
+}
+
 export const LANG_MAP: Record<string, string> = {
   ts: 'typescript', tsx: 'tsx', js: 'javascript', jsx: 'jsx',
   mjs: 'javascript', cjs: 'javascript',