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/config/checkpointer_config.py

@@ -0,0 +1,46 @@
+"""Configuration for LangGraph checkpointer."""
+
+from typing import Literal
+
+from pydantic import BaseModel, Field
+
+CheckpointerType = Literal["memory", "sqlite", "postgres"]
+
+
+class CheckpointerConfig(BaseModel):
+    """Configuration for LangGraph state persistence checkpointer."""
+
+    type: CheckpointerType = Field(
+        description="Checkpointer backend type. "
+        "'memory' is in-process only (lost on restart). "
+        "'sqlite' persists to a local file (requires langgraph-checkpoint-sqlite). "
+        "'postgres' persists to PostgreSQL (requires langgraph-checkpoint-postgres)."
+    )
+    connection_string: str | None = Field(
+        default=None,
+        description="Connection string for sqlite (file path) or postgres (DSN). "
+        "Required for sqlite and postgres types. "
+        "For sqlite, use a file path like '.deer-flow/checkpoints.db' or ':memory:' for in-memory. "
+        "For postgres, use a DSN like 'postgresql://user:pass@localhost:5432/db'.",
+    )
+
+
+# Global configuration instance — None means no checkpointer is configured.
+_checkpointer_config: CheckpointerConfig | None = None
+
+
+def get_checkpointer_config() -> CheckpointerConfig | None:
+    """Get the current checkpointer configuration, or None if not configured."""
+    return _checkpointer_config
+
+
+def set_checkpointer_config(config: CheckpointerConfig | None) -> None:
+    """Set the checkpointer configuration."""
+    global _checkpointer_config
+    _checkpointer_config = config
+
+
+def load_checkpointer_config_from_dict(config_dict: dict) -> None:
+    """Load checkpointer configuration from a dictionary."""
+    global _checkpointer_config
+    _checkpointer_config = CheckpointerConfig(**config_dict)