Initial commit: hardened DeerFlow factory

Vendored deer-flow upstream (bytedance/deer-flow) plus prompt-injection
hardening:

- New deerflow.security package: content_delimiter, html_cleaner,
  sanitizer (8 layers — invisible chars, control chars, symbols, NFC,
  PUA, tag chars, horizontal whitespace collapse with newline/tab
  preservation, length cap)
- New deerflow.community.searx package: web_search, web_fetch,
  image_search backed by a private SearX instance, every external
  string sanitized and wrapped in <<<EXTERNAL_UNTRUSTED_CONTENT>>>
  delimiters
- All native community web providers (ddg_search, tavily, exa,
  firecrawl, jina_ai, infoquest, image_search) replaced with hard-fail
  stubs that raise NativeWebToolDisabledError at import time, so a
  misconfigured tool.use path fails loud rather than silently falling
  back to unsanitized output
- Native client back-doors (jina_client.py, infoquest_client.py)
  stubbed too
- Native-tool tests quarantined under tests/_disabled_native/
  (collect_ignore_glob via local conftest.py)
- Sanitizer Layer 7 fix: only collapse horizontal whitespace, preserve
  newlines and tabs so list/table structure survives
- Hardened runtime config.yaml references only the searx-backed tools
- Factory overlay (backend/) kept in sync with deer-flow tree as a
  reference / source

See HARDENING.md for the full audit trail and verification steps.

backend/tests/test_searx_tools.py

@@ -0,0 +1,15 @@
+"""Integration tests for hardened web tools."""
+
+import pytest
+from deerflow.community.searx.tools import web_search_tool
+
+
+class TestHardenedSearxSearch:
+    """Test hardened SearX search against prompt injection."""
+    
+    def test_search_results_are_delimited(self):
+        """Results must be wrapped in security delimiters."""
+        result = web_search_tool("test query")
+        
+        assert "<<<EXTERNAL_UNTRUSTED_CONTENT>>>" in result
+        assert "<<<END_EXTERNAL_UNTRUSTED_CONTENT>>>" in result

backend/tests/test_security_html_cleaner.py

@@ -0,0 +1,15 @@
+"""Tests for HTML cleaner."""
+
+import pytest
+from deerflow.security.html_cleaner import extract_secure_text
+
+
+def test_html_scripts_are_removed():
+    """Script tags must be stripped."""
+    html = "<p>Hello</p><script>alert('xss')</script><p>World</p>"
+    result = extract_secure_text(html)
+    
+    assert "script" not in result.lower()
+    assert "alert" not in result
+    assert "Hello" in result
+    assert "World" in result

backend/tests/test_security_sanitizer.py

@@ -0,0 +1,72 @@
+"""Tests for prompt injection sanitizer."""
+
+import pytest
+from deerflow.security.sanitizer import PromptInjectionSanitizer
+
+
+class TestPromptInjectionSanitizer:
+    """Test cases based on OpenClaw patterns."""
+    
+    def test_removes_zero_width_spaces(self):
+        """Zero-width characters are common steganography vectors."""
+        sanitizer = PromptInjectionSanitizer()
+        text = "Hello\u200bWorld\u200c"  # ZWSP and ZWNJ
+        result = sanitizer.sanitize(text)
+        assert "\u200b" not in result
+        assert "\u200c" not in result
+        assert result == "HelloWorld"
+    
+    def test_removes_control_chars(self):
+        """Control chars can disrupt prompt parsing."""
+        sanitizer = PromptInjectionSanitizer()
+        text = "Hello\x00World\x01Test"
+        result = sanitizer.sanitize(text)
+        assert "\x00" not in result
+        assert "\x01" not in result
+        assert "Hello" in result
+    
+    def test_preserves_newlines_and_tabs(self):
+        """Structural characters should be preserved."""
+        sanitizer = PromptInjectionSanitizer()
+        text = "Line1\nLine2\tTabbed"
+        result = sanitizer.sanitize(text)
+        assert "\n" in result
+        assert "\t" in result
+    
+    def test_truncates_long_content(self):
+        """Length limiting prevents context overflow."""
+        sanitizer = PromptInjectionSanitizer()
+        text = "A" * 1000
+        result = sanitizer.sanitize(text, max_length=100)
+        assert len(result) == 100
+        assert result.endswith("...")
+    
+    def test_handles_pua_characters(self):
+        """Private Use Area chars can encode hidden data."""
+        sanitizer = PromptInjectionSanitizer()
+        text = "Hello\uE000World"  # PUA start
+        result = sanitizer.sanitize(text)
+        assert "\uE000" not in result
+
+
+class TestContentDelimiter:
+    """Test delimiter wrapping."""
+    
+    def test_wraps_dict_content(self):
+        from deerflow.security.content_delimiter import wrap_untrusted_content
+        
+        content = {"title": "Test", "url": "http://example.com"}
+        result = wrap_untrusted_content(content)
+        
+        assert "<<<EXTERNAL_UNTRUSTED_CONTENT>>>" in result
+        assert "<<<END_EXTERNAL_UNTRUSTED_CONTENT>>>" in result
+        assert "Test" in result
+    
+    def test_wraps_string_content(self):
+        from deerflow.security.content_delimiter import wrap_untrusted_content
+        
+        content = "Raw text from web"
+        result = wrap_untrusted_content(content)
+        
+        assert "<<<EXTERNAL_UNTRUSTED_CONTENT>>>" in result
+        assert "Raw text from web" in result