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/packages/harness/deerflow/sandbox/sandbox_provider.py

@@ -0,0 +1,96 @@
+from abc import ABC, abstractmethod
+
+from deerflow.config import get_app_config
+from deerflow.reflection import resolve_class
+from deerflow.sandbox.sandbox import Sandbox
+
+
+class SandboxProvider(ABC):
+    """Abstract base class for sandbox providers"""
+
+    @abstractmethod
+    def acquire(self, thread_id: str | None = None) -> str:
+        """Acquire a sandbox environment and return its ID.
+
+        Returns:
+            The ID of the acquired sandbox environment.
+        """
+        pass
+
+    @abstractmethod
+    def get(self, sandbox_id: str) -> Sandbox | None:
+        """Get a sandbox environment by ID.
+
+        Args:
+            sandbox_id: The ID of the sandbox environment to retain.
+        """
+        pass
+
+    @abstractmethod
+    def release(self, sandbox_id: str) -> None:
+        """Release a sandbox environment.
+
+        Args:
+            sandbox_id: The ID of the sandbox environment to destroy.
+        """
+        pass
+
+
+_default_sandbox_provider: SandboxProvider | None = None
+
+
+def get_sandbox_provider(**kwargs) -> SandboxProvider:
+    """Get the sandbox provider singleton.
+
+    Returns a cached singleton instance. Use `reset_sandbox_provider()` to clear
+    the cache, or `shutdown_sandbox_provider()` to properly shutdown and clear.
+
+    Returns:
+        A sandbox provider instance.
+    """
+    global _default_sandbox_provider
+    if _default_sandbox_provider is None:
+        config = get_app_config()
+        cls = resolve_class(config.sandbox.use, SandboxProvider)
+        _default_sandbox_provider = cls(**kwargs)
+    return _default_sandbox_provider
+
+
+def reset_sandbox_provider() -> None:
+    """Reset the sandbox provider singleton.
+
+    This clears the cached instance without calling shutdown.
+    The next call to `get_sandbox_provider()` will create a new instance.
+    Useful for testing or when switching configurations.
+
+    Note: If the provider has active sandboxes, they will be orphaned.
+    Use `shutdown_sandbox_provider()` for proper cleanup.
+    """
+    global _default_sandbox_provider
+    _default_sandbox_provider = None
+
+
+def shutdown_sandbox_provider() -> None:
+    """Shutdown and reset the sandbox provider.
+
+    This properly shuts down the provider (releasing all sandboxes)
+    before clearing the singleton. Call this when the application
+    is shutting down or when you need to completely reset the sandbox system.
+    """
+    global _default_sandbox_provider
+    if _default_sandbox_provider is not None:
+        if hasattr(_default_sandbox_provider, "shutdown"):
+            _default_sandbox_provider.shutdown()
+        _default_sandbox_provider = None
+
+
+def set_sandbox_provider(provider: SandboxProvider) -> None:
+    """Set a custom sandbox provider instance.
+
+    This allows injecting a custom or mock provider for testing purposes.
+
+    Args:
+        provider: The SandboxProvider instance to use.
+    """
+    global _default_sandbox_provider
+    _default_sandbox_provider = provider