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.

deer-flow/backend/tests/test_mcp_client_config.py

@@ -0,0 +1,93 @@
+"""Core behavior tests for MCP client server config building."""
+
+import pytest
+
+from deerflow.config.extensions_config import ExtensionsConfig, McpServerConfig
+from deerflow.mcp.client import build_server_params, build_servers_config
+
+
+def test_build_server_params_stdio_success():
+    config = McpServerConfig(
+        type="stdio",
+        command="npx",
+        args=["-y", "my-mcp-server"],
+        env={"API_KEY": "secret"},
+    )
+
+    params = build_server_params("my-server", config)
+
+    assert params == {
+        "transport": "stdio",
+        "command": "npx",
+        "args": ["-y", "my-mcp-server"],
+        "env": {"API_KEY": "secret"},
+    }
+
+
+def test_build_server_params_stdio_requires_command():
+    config = McpServerConfig(type="stdio", command=None)
+
+    with pytest.raises(ValueError, match="requires 'command' field"):
+        build_server_params("broken-stdio", config)
+
+
+@pytest.mark.parametrize("transport", ["sse", "http"])
+def test_build_server_params_http_like_success(transport: str):
+    config = McpServerConfig(
+        type=transport,
+        url="https://example.com/mcp",
+        headers={"Authorization": "Bearer token"},
+    )
+
+    params = build_server_params("remote-server", config)
+
+    assert params == {
+        "transport": transport,
+        "url": "https://example.com/mcp",
+        "headers": {"Authorization": "Bearer token"},
+    }
+
+
+@pytest.mark.parametrize("transport", ["sse", "http"])
+def test_build_server_params_http_like_requires_url(transport: str):
+    config = McpServerConfig(type=transport, url=None)
+
+    with pytest.raises(ValueError, match="requires 'url' field"):
+        build_server_params("broken-remote", config)
+
+
+def test_build_server_params_rejects_unsupported_transport():
+    config = McpServerConfig(type="websocket")
+
+    with pytest.raises(ValueError, match="unsupported transport type"):
+        build_server_params("bad-transport", config)
+
+
+def test_build_servers_config_returns_empty_when_no_enabled_servers():
+    extensions = ExtensionsConfig(
+        mcp_servers={
+            "disabled-a": McpServerConfig(enabled=False, type="stdio", command="echo"),
+            "disabled-b": McpServerConfig(enabled=False, type="http", url="https://example.com"),
+        },
+        skills={},
+    )
+
+    assert build_servers_config(extensions) == {}
+
+
+def test_build_servers_config_skips_invalid_server_and_keeps_valid_ones():
+    extensions = ExtensionsConfig(
+        mcp_servers={
+            "valid-stdio": McpServerConfig(enabled=True, type="stdio", command="npx", args=["server"]),
+            "invalid-stdio": McpServerConfig(enabled=True, type="stdio", command=None),
+            "disabled-http": McpServerConfig(enabled=False, type="http", url="https://disabled.example.com"),
+        },
+        skills={},
+    )
+
+    result = build_servers_config(extensions)
+
+    assert "valid-stdio" in result
+    assert result["valid-stdio"]["transport"] == "stdio"
+    assert "invalid-stdio" not in result
+    assert "disabled-http" not in result