fix: validate URL scheme in fetch_webpage to reject file:// URLs (#8889)

Adds validation to the fetch_webpage tool to ensure only HTTP/HTTPS URLs
are accepted. Previously, passing a file:// URL would cause an unhandled
requests.exceptions.InvalidSchema error. Now it raises a clear ValueError
with a helpful error message.

Fixes: requests.exceptions.InvalidSchema: No connection adapters were found for 'file://...'

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Co-authored-by: letta-code <248085862+letta-code@users.noreply.github.com>
Co-authored-by: datadog-official[bot] <datadog-official[bot]@users.noreply.github.com>
Co-authored-by: Letta <noreply@letta.com>
Co-authored-by: Kian Jones <11655409+kianjones9@users.noreply.github.com>

letta/services/tool_executor/builtin_tool_executor.py

@@ -320,12 +320,21 @@ class LettaBuiltinToolExecutor(ToolExecutor):
             String containing the webpage content in markdown/text format
         """
         import asyncio
+        from urllib.parse import urlparse
 
         import html2text
         import requests
         from readability import Document
         from trafilatura import extract, fetch_url
 
+        # Validate URL scheme - only HTTP and HTTPS are supported
+        parsed_url = urlparse(url)
+        if parsed_url.scheme.lower() not in ("http", "https"):
+            raise ValueError(
+                f"Invalid URL scheme '{parsed_url.scheme}'. Only 'http' and 'https' URLs are supported. "
+                f"Local file paths (file://) and other protocols cannot be fetched."
+            )
+
         # Try exa first
         try:
             from exa_py import Exa