Latest Results
chore(langchain): satisfy lint and type checks on eval framework
Fixes ruff (D301, F401, ANN202, PLC0415, PERF401, PLE2515, ARG002, T201,
TRY003, EM102, E501) and mypy (call-overload on `init_chat_model` and
`agent.invoke`) violations introduced by the new `tests/evals/` files.
No behavior change; pure conformance with the langchain_v1 lint/type
configuration. Test collection still finds the same 6 tests.nh/todo-middleware-loop-contract feat(langchain): redact streamed PII in flight on `PIIMiddleware` (#37616)
`PIIMiddleware` previously scrubbed detected PII only at the state level
via its `after_model` / `before_model` hooks. Consumers reading the live
stream — `astream_events(version="v3")` or `run.messages` /
`run.tool_calls` / `run.values` — saw the raw model text, the raw
tool-call args, the raw tool outputs, and the raw state snapshots until
the run finished and the canonical conversation history was written.
This change registers a stream transformer ahead of
`MessagesTransformer` that redacts every wire surface of an agent run.
The transformer holds a sliding lookback buffer (default 128 characters)
per `(run_id, content-block index)` so PII patterns that straddle delta
boundaries are caught before the safe prefix is released downstream.
Anything older than the lookback is run through the configured detector
and emitted; the trailing tail stays buffered until a later delta
extends it past the cap or the block finishes. `_finalize_block` always
re-runs detection over the full block snapshot so the finalized content
lands fully redacted even when the in-flight buffer never released a
tail (short responses, or PII arriving in the final delta).
The `block` strategy is now supported on the streaming path via a
buffering mode that withholds every delta until the block resolves —
clean blocks release the full text at finalize, PII-bearing blocks zero
the wire and let `after_model` / `apply_to_tool_results` raise
`PIIDetectionError` on the original state message. Activation is gated
on `apply_to_output=True`, matching the existing post-hoc semantics. The
middleware's transformer factory is cloned by `StreamMux._make_child`
into every subgraph scope, so attaching `PIIMiddleware` at the outer
agent also redacts streamed deltas from sub-agents invoked inside tools.
## Tool-call and tools-channel coverage
The transformer covers every wire surface of an agent run, not just AI
message text:
- **Streamed AI text deltas** (`content-block-delta` of type
`text-delta`) — lookback machinery, redacted in place.
- **Streamed tool-call args** (`content-block-delta` with
`tool_call_chunk` / `server_tool_call_chunk` fields) — each delta
carries the full cumulative args string; detection runs on the field
directly and redacts in place. Verified empirically against
`_compat_bridge.py` and the consumer-side
`_merge_block_delta_into_store` snapshot-replace semantics.
- **Finalized tool-call blocks** (`content-block-finish` with
`tool_call` / `server_tool_call` / `invalid_tool_call`) — `args` dict
walked recursively and each string leaf redacted.
- **Tool execution events on the `tools` channel** —
`tool-started.input`, `tool-output-delta`, `tool-finished.output`,
`tool-error.message` all run through detection. String deltas use the
same lookback machinery as text-deltas keyed by `tool_call_id`;
structured payloads walk recursively.
- **State snapshots on the `values` channel** — message lists are walked
and each message's `.content` is redacted on a fresh copy. Graph state
itself stays intact for the state-level enforcer
(`apply_to_tool_results` via `before_model`) to act on independently.
- **Legacy `(BaseMessage, metadata)` payloads** on the `messages`
channel (Python 3.10 path, where `langgraph`'s `ASYNCIO_ACCEPTS_CONTEXT
= sys.version_info >= (3, 11)` falls back to a code path that doesn't
propagate the streaming callback into the chat model) — `.content` and
`AIMessage.tool_calls[*].args` are scrubbed. For `block`, the event's
`data` tuple is replaced with an empty-content copy so the original
message stays in state for `after_model` to raise on.
## Worth a careful look
- `_PIIStreamTransformer._mutate_text_delta` — lookback partition.
Anything older than `lookback` characters is released after redaction;
the tail stays buffered. Bulletproof against whitespace-permissive
detectors (notably `credit_card`, whose regex matches across spaces).
- `_PIIStreamTransformer._mutate_tool_call_chunk_delta` — direct
in-place redaction of the cumulative args string. No buffer; the wire
shape is cumulative-snapshot, the consumer-side merge is
replace-not-append.
- `_PIIStreamTransformer._mutate_legacy_payload` — the dual path:
mutate-in-place for non-`block` (idempotent with `after_model`),
replace-with-empty-copy for `block` (keeps original in graph state for
`after_model` to raise on).
- `_PIIStreamTransformer._redact_value` — the recursive walker.
`BaseMessage` branch returns a fresh `.content`-redacted copy via
`model_copy(update=...)` — never mutates in place — so tool-output
payloads that wrap a `ToolMessage` and message lists in state snapshots
flow through cleanly.
- The new `transformers` attribute on `PIIMiddleware`: this is what
makes `create_agent` pick the factory up. Multiple `PIIMiddleware`
instances each register one transformer; ordering is preserved within
the `before_builtins` lane.
## Compatibility
Bumps `langgraph` to `>=1.2.1` for the `before_builtins` opt-in on
`StreamTransformer`. Latest Branches
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nh/todo-middleware-loop-contract 0%
nh/pii-middleware-stream-redaction +11%
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