feat(agent): scrape linked pages to ground answers in real content

Adds `_fetch_page_content()`, which downloads a URL with a
browser-like User-Agent and uses BeautifulSoup with the lxml
parser to strip scripts, navigation, and other non-content
markup, returning up to 3000 characters of readable text.

The response validator now also compares generated replies
against this scraped text, flagging named entities and claims
that do not appear in the retrieved page content.

Dependencies: adds beautifulsoup4==4.12.3 and pins lxml==5.3.0
for parser compatibility.

venv/lib/python3.11/site-packages/lxml/includes/libxml/xmlerror.h

@@ -16,12 +16,6 @@
 extern "C" {
 #endif
 
-/*
- * Backward compatibility
- */
-#define initGenericErrorDefaultFunc(h) \
-    xmlSetGenericErrorFunc(NULL, (h) ? *((xmlGenericErrorFunc *) (h)) : NULL)
-
 /**
  * xmlErrorLevel:
  *
@@ -217,11 +211,6 @@ typedef enum {
     XML_ERR_USER_STOP, /* 111 */
     XML_ERR_COMMENT_ABRUPTLY_ENDED, /* 112 */
     XML_WAR_ENCODING_MISMATCH, /* 113 */
-    XML_ERR_RESOURCE_LIMIT, /* 114 */
-    XML_ERR_ARGUMENT, /* 115 */
-    XML_ERR_SYSTEM, /* 116 */
-    XML_ERR_REDECL_PREDEF_ENTITY, /* 117 */
-    XML_ERR_INT_SUBSET_NOT_FINISHED, /* 118 */
     XML_NS_ERR_XML_NAMESPACE = 200,
     XML_NS_ERR_UNDEFINED_NAMESPACE, /* 201 */
     XML_NS_ERR_QNAME, /* 202 */
@@ -484,7 +473,6 @@ typedef enum {
     XML_IO_EADDRINUSE, /* 1554 */
     XML_IO_EALREADY, /* 1555 */
     XML_IO_EAFNOSUPPORT, /* 1556 */
-    XML_IO_UNSUPPORTED_PROTOCOL, /* 1557 */
     XML_XINCLUDE_RECURSION=1600,
     XML_XINCLUDE_PARSE_VALUE, /* 1601 */
     XML_XINCLUDE_ENTITY_DEF_MISMATCH, /* 1602 */
@@ -871,20 +859,23 @@ typedef void (*xmlGenericErrorFunc) (void *ctx,
 typedef void (*xmlStructuredErrorFunc) (void *userData, const xmlError *error);
 
 /** DOC_DISABLE */
-XML_DEPRECATED
-XMLPUBFUN const xmlError *__xmlLastError(void);
+#define XML_GLOBALS_ERROR \
+  XML_OP(xmlLastError, xmlError, XML_DEPRECATED) \
+  XML_OP(xmlGenericError, xmlGenericErrorFunc, XML_NO_ATTR) \
+  XML_OP(xmlGenericErrorContext, void *, XML_NO_ATTR) \
+  XML_OP(xmlStructuredError, xmlStructuredErrorFunc, XML_NO_ATTR) \
+  XML_OP(xmlStructuredErrorContext, void *, XML_NO_ATTR)
 
-XMLPUBFUN xmlGenericErrorFunc *__xmlGenericError(void);
-XMLPUBFUN void **__xmlGenericErrorContext(void);
-XMLPUBFUN xmlStructuredErrorFunc *__xmlStructuredError(void);
-XMLPUBFUN void **__xmlStructuredErrorContext(void);
+#define XML_OP XML_DECLARE_GLOBAL
+XML_GLOBALS_ERROR
+#undef XML_OP
 
-#ifndef XML_GLOBALS_NO_REDEFINITION
-  #define xmlLastError (*__xmlLastError())
-  #define xmlGenericError (*__xmlGenericError())
-  #define xmlGenericErrorContext (*__xmlGenericErrorContext())
-  #define xmlStructuredError (*__xmlStructuredError())
-  #define xmlStructuredErrorContext (*__xmlStructuredErrorContext())
+#if defined(LIBXML_THREAD_ENABLED) && !defined(XML_GLOBALS_NO_REDEFINITION)
+  #define xmlLastError XML_GLOBAL_MACRO(xmlLastError)
+  #define xmlGenericError XML_GLOBAL_MACRO(xmlGenericError)
+  #define xmlGenericErrorContext XML_GLOBAL_MACRO(xmlGenericErrorContext)
+  #define xmlStructuredError XML_GLOBAL_MACRO(xmlStructuredError)
+  #define xmlStructuredErrorContext XML_GLOBAL_MACRO(xmlStructuredErrorContext)
 #endif
 /** DOC_ENABLE */
 
@@ -895,15 +886,16 @@ XMLPUBFUN void **__xmlStructuredErrorContext(void);
 XMLPUBFUN void
     xmlSetGenericErrorFunc	(void *ctx,
 				 xmlGenericErrorFunc handler);
-XML_DEPRECATED
 XMLPUBFUN void
     xmlThrDefSetGenericErrorFunc(void *ctx,
                                  xmlGenericErrorFunc handler);
+XML_DEPRECATED
+XMLPUBFUN void
+    initGenericErrorDefaultFunc	(xmlGenericErrorFunc *handler);
 
 XMLPUBFUN void
     xmlSetStructuredErrorFunc	(void *ctx,
 				 xmlStructuredErrorFunc handler);
-XML_DEPRECATED
 XMLPUBFUN void
     xmlThrDefSetStructuredErrorFunc(void *ctx,
                                  xmlStructuredErrorFunc handler);
@@ -927,17 +919,11 @@ XMLPUBFUN void
     xmlParserValidityWarning	(void *ctx,
 				 const char *msg,
 				 ...) LIBXML_ATTR_FORMAT(2,3);
-/** DOC_DISABLE */
 struct _xmlParserInput;
-/** DOC_ENABLE */
 XMLPUBFUN void
     xmlParserPrintFileInfo	(struct _xmlParserInput *input);
 XMLPUBFUN void
     xmlParserPrintFileContext	(struct _xmlParserInput *input);
-XMLPUBFUN void
-xmlFormatError			(const xmlError *err,
-				 xmlGenericErrorFunc channel,
-				 void *data);
 
 /*
  * Extended error information routines