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/conftest.py

@@ -0,0 +1,55 @@
+"""Test configuration for the backend test suite.
+
+Sets up sys.path and pre-mocks modules that would cause circular import
+issues when unit-testing lightweight config/registry code in isolation.
+"""
+
+import importlib.util
+import sys
+from pathlib import Path
+from unittest.mock import MagicMock
+
+import pytest
+
+# Make 'app' and 'deerflow' importable from any working directory
+sys.path.insert(0, str(Path(__file__).parent.parent))
+sys.path.insert(0, str(Path(__file__).resolve().parents[2] / "scripts"))
+
+# Break the circular import chain that exists in production code:
+#   deerflow.subagents.__init__
+#     -> .executor (SubagentExecutor, SubagentResult)
+#       -> deerflow.agents.thread_state
+#         -> deerflow.agents.__init__
+#           -> lead_agent.agent
+#             -> subagent_limit_middleware
+#               -> deerflow.subagents.executor  <-- circular!
+#
+# By injecting a mock for deerflow.subagents.executor *before* any test module
+# triggers the import, __init__.py's "from .executor import ..." succeeds
+# immediately without running the real executor module.
+_executor_mock = MagicMock()
+_executor_mock.SubagentExecutor = MagicMock
+_executor_mock.SubagentResult = MagicMock
+_executor_mock.SubagentStatus = MagicMock
+_executor_mock.MAX_CONCURRENT_SUBAGENTS = 3
+_executor_mock.get_background_task_result = MagicMock()
+
+sys.modules["deerflow.subagents.executor"] = _executor_mock
+
+
+@pytest.fixture()
+def provisioner_module():
+    """Load docker/provisioner/app.py as an importable test module.
+
+    Shared by test_provisioner_kubeconfig and test_provisioner_pvc_volumes so
+    that any change to the provisioner entry-point path or module name only
+    needs to be updated in one place.
+    """
+    repo_root = Path(__file__).resolve().parents[2]
+    module_path = repo_root / "docker" / "provisioner" / "app.py"
+    spec = importlib.util.spec_from_file_location("provisioner_app_test", module_path)
+    assert spec is not None
+    assert spec.loader is not None
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module