feat: implement Anthropic native PDF support with document preservation

- Add comprehensive debug logging throughout PDF processing pipeline
- Refactor attachment processing to separate image and document handling
- Create distinct addImageURLs(), addDocuments(), and processAttachments() methods
- Fix critical bugs in stream handling and parameter passing
- Add streamToBuffer utility for proper stream-to-buffer conversion
- Remove api/agents submodule from repository

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

api/server/services/Files/validation/pdfValidator.js

@@ -0,0 +1,77 @@
+const { logger } = require('~/config');
+const { anthropicPdfSizeLimit } = require('librechat-data-provider');
+
+/**
+ * Validates if a PDF meets Anthropic's requirements
+ * @param {Buffer} pdfBuffer - The PDF file as a buffer
+ * @param {number} fileSize - The file size in bytes
+ * @returns {Promise<{isValid: boolean, error?: string}>}
+ */
+async function validateAnthropicPdf(pdfBuffer, fileSize) {
+  try {
+    // Check file size (32MB limit)
+    if (fileSize > anthropicPdfSizeLimit) {
+      return {
+        isValid: false,
+        error: `PDF file size (${Math.round(fileSize / (1024 * 1024))}MB) exceeds Anthropic's 32MB limit`,
+      };
+    }
+
+    // Basic PDF header validation
+    if (!pdfBuffer || pdfBuffer.length < 5) {
+      return {
+        isValid: false,
+        error: 'Invalid PDF file: too small or corrupted',
+      };
+    }
+
+    // Check PDF magic bytes
+    const pdfHeader = pdfBuffer.subarray(0, 5).toString();
+    if (!pdfHeader.startsWith('%PDF-')) {
+      return {
+        isValid: false,
+        error: 'Invalid PDF file: missing PDF header',
+      };
+    }
+
+    // Check for password protection/encryption
+    const pdfContent = pdfBuffer.toString('binary');
+    if (
+      pdfContent.includes('/Encrypt ') ||
+      pdfContent.includes('/U (') ||
+      pdfContent.includes('/O (')
+    ) {
+      return {
+        isValid: false,
+        error: 'PDF is password-protected or encrypted. Anthropic requires unencrypted PDFs.',
+      };
+    }
+
+    // Estimate page count (this is a rough estimation)
+    const pageMatches = pdfContent.match(/\/Type[\s]*\/Page[^s]/g);
+    const estimatedPages = pageMatches ? pageMatches.length : 1;
+
+    if (estimatedPages > 100) {
+      return {
+        isValid: false,
+        error: `PDF has approximately ${estimatedPages} pages, exceeding Anthropic's 100-page limit`,
+      };
+    }
+
+    logger.debug(
+      `PDF validation passed: ${Math.round(fileSize / 1024)}KB, ~${estimatedPages} pages`,
+    );
+
+    return { isValid: true };
+  } catch (error) {
+    logger.error('PDF validation error:', error);
+    return {
+      isValid: false,
+      error: 'Failed to validate PDF file',
+    };
+  }
+}
+
+module.exports = {
+  validateAnthropicPdf,
+};