LangChain Redaction Node¶

OpenMed provides a local redaction node for LangChain chains. It redacts document text and message content before a downstream prompt or model, while preserving message order and copying metadata unchanged. LangChain remains an optional dependency:

pip install "openmed[langchain]"

Add the node before a chain step¶

create_redaction_node() loads langchain-core only when the node is created. The default policy is explicit (hipaa_safe_harbor), masking is deterministic, and the adapter does not call a hosted service.

from openmed.interop.langchain import create_redaction_node

redact = create_redaction_node(policy="strict_no_leak")
safe_chain = redact | downstream_chain

result = safe_chain.invoke("Summarize the synthetic clinical note.")

The node accepts strings, LangChain Document objects, message objects, lists, tuples, and mapping payloads. Document and message objects are copied; their metadata and ordering are retained. Multimodal message content redacts text blocks and leaves non-text blocks unchanged.

from openmed.interop.langchain import create_redaction_node

redact = create_redaction_node(
    input_key="messages",
    policy="strict_no_leak",
)

payload = redact.invoke(
    {
        "messages": [
            {"role": "user", "content": "Synthetic Name needs a follow-up."},
            {"role": "assistant", "content": "The appointment is synthetic."},
        ],
        "metadata": {"source": "synthetic-fixture"},
    }
)

Use create_redaction_transform() when a LangChain dependency is not needed, such as in an offline unit test. It exposes the same invoke, batch, and transform shape without importing LangChain.

Deterministic replacements¶

Masking is the safest default. If a reviewed workflow uses replace or format_preserve, pass request-local replacement controls so separate messages share deterministic surrogate behavior. The state stores only the seed and aggregate counters; it never stores source text or a re-identification map.

from openmed.interop.langchain import (
    LangChainRedactionConfig,
    LangChainRedactionState,
    create_redaction_node,
)

replacement_state = LangChainRedactionState(seed=17)
redact = create_redaction_node(
    config=LangChainRedactionConfig(
        method="replace",
        policy="strict_no_leak",
    ),
    replacement_state=replacement_state,
)

The optional adapter fails with an actionable openmed[langchain] installation message when langchain-core is missing. Deidentifier failures are surfaced as safe adapter errors without embedding input content in exception text.