feat(prebuilt): hydrate ToolNode state from channels via CONFIG_KEY_READ

When ToolNode receives a bare `[tool_call]` list via the Send API (the
new dispatch shape that create_agent uses after langchain-ai/langchain
drops the ToolCallWithContext wrapper), hydrate ToolRuntime.state from
the current channel values instead of requiring the dispatcher to
inline the full agent state dict in the Send payload.

Implementation stays entirely in tool_node:

- Pregel installs CONFIG_KEY_READ as
  `functools.partial(local_read, scratchpad, channels, managed, task)`.
  Introspect the partial's positional args to learn channel + managed
  names, then read them all via `ChannelRead.do_read` with an explicit
  list. No changes to the pregel read machinery.
- Gracefully falls back to {} when invoked outside a Pregel context
  (e.g. direct ToolNode(...).invoke(...) from test harnesses).
- Legacy ToolCallWithContext path is preserved for external dispatchers.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

libs/langgraph/langgraph/graph/message.py

@@ -184,63 +184,97 @@ def add_messages(
         ```
 
     """
-    remove_all_idx = None
-    # coerce to list
+    # 1. Coerce scalars to lists.
     if not isinstance(left, list):
         left = [left]  # type: ignore[assignment]
     if not isinstance(right, list):
         right = [right]  # type: ignore[assignment]
-    # coerce to message
-    left = [
-        message_chunk_to_message(cast(BaseMessageChunk, m))
-        for m in convert_to_messages(left)
-    ]
-    right = [
+    left = cast(list, left)
+
+    # 2. Normalize `left`. After the first call, `left` is the previous return
+    #    value of `add_messages` — a list of fully-resolved BaseMessages with
+    #    IDs — and needs no work. Fresh user input (dicts, tuples, message
+    #    chunks, BaseMessages without IDs) falls through to full conversion.
+    left_msgs: list[BaseMessage]
+    if (
+        left
+        and isinstance(left[0], BaseMessage)
+        and not isinstance(left[0], BaseMessageChunk)
+        and left[0].id is not None
+    ):
+        left_msgs = left
+    else:
+        left_msgs = [
+            message_chunk_to_message(cast(BaseMessageChunk, m))
+            for m in convert_to_messages(left)
+        ]
+        for m in left_msgs:
+            if m.id is None:
+                m.id = str(uuid.uuid4())
+
+    # 3. Normalize `right` — always fresh input. Assign missing IDs and detect
+    #    any RemoveMessage sentinels in a single pass.
+    right_msgs: list[BaseMessage] = [
         message_chunk_to_message(cast(BaseMessageChunk, m))
         for m in convert_to_messages(right)
     ]
-    # assign missing ids
-    for m in left:
+    remove_all_idx: int | None = None
+    has_remove = False
+    for idx, m in enumerate(right_msgs):
         if m.id is None:
             m.id = str(uuid.uuid4())
-    for idx, m in enumerate(right):
-        if m.id is None:
-            m.id = str(uuid.uuid4())
-        if isinstance(m, RemoveMessage) and m.id == REMOVE_ALL_MESSAGES:
-            remove_all_idx = idx
+        if isinstance(m, RemoveMessage):
+            has_remove = True
+            if m.id == REMOVE_ALL_MESSAGES:
+                remove_all_idx = idx
 
+    # 4. REMOVE_ALL_MESSAGES: discard everything up to and including the sentinel.
     if remove_all_idx is not None:
-        return right[remove_all_idx + 1 :]
+        return right_msgs[remove_all_idx + 1 :]
 
-    # merge
-    merged = left.copy()
-    merged_by_id = {m.id: i for i, m in enumerate(merged)}
-    ids_to_remove = set()
-    for m in right:
-        if (existing_idx := merged_by_id.get(m.id)) is not None:
-            if isinstance(m, RemoveMessage):
-                ids_to_remove.add(m.id)
+    # 5. Decide fast vs. slow path. The fast path (pure append) is only valid
+    #    when `right` has no removals, no intra-right duplicate IDs, and no IDs
+    #    that overlap with `left` — any of those would force the indexed merge
+    #    below to update or dedup.
+    pure_append = False
+    if not has_remove:
+        left_ids = {m.id for m in left_msgs}
+        right_ids = {m.id for m in right_msgs}
+        pure_append = len(right_ids) == len(right_msgs) and right_ids.isdisjoint(
+            left_ids
+        )
+
+    if pure_append:
+        merged = left_msgs + right_msgs
+    else:
+        # 6. Slow path: build id→index map over `left`, then replay `right`.
+        #    In-place replacement for matching IDs, append for new IDs, and a
+        #    deferred removal pass so RemoveMessages can target either side.
+        merged = left_msgs.copy()
+        merged_by_id = {m.id: i for i, m in enumerate(merged)}
+        ids_to_remove = set()
+        for m in right_msgs:
+            if (existing_idx := merged_by_id.get(m.id)) is not None:
+                if isinstance(m, RemoveMessage):
+                    ids_to_remove.add(m.id)
+                else:
+                    ids_to_remove.discard(m.id)
+                    merged[existing_idx] = m
             else:
-                ids_to_remove.discard(m.id)
-                merged[existing_idx] = m
-        else:
-            if isinstance(m, RemoveMessage):
-                raise ValueError(
-                    f"Attempting to delete a message with an ID that doesn't exist ('{m.id}')"
-                )
-
-            merged_by_id[m.id] = len(merged)
-            merged.append(m)
-    merged = [m for m in merged if m.id not in ids_to_remove]
+                if isinstance(m, RemoveMessage):
+                    raise ValueError(
+                        f"Attempting to delete a message with an ID that doesn't exist ('{m.id}')"
+                    )
+                merged_by_id[m.id] = len(merged)
+                merged.append(m)
+        merged = [m for m in merged if m.id not in ids_to_remove]
 
+    # 7. Apply optional output format.
     if format == "langchain-openai":
-        merged = _format_messages(merged)
-    elif format:
+        return _format_messages(merged)
+    if format:
         msg = f"Unrecognized {format=}. Expected one of 'langchain-openai', None."
         raise ValueError(msg)
-    else:
-        pass
-
     return merged
 
 

libs/langgraph/tests/test_add_messages_benchmark.py

@@ -0,0 +1,290 @@
+"""Benchmark: add_messages fast-path optimizations.
+
+Both implementations are inlined so the benchmark is self-contained and
+immune to import-cache or installed-vs-local confusion.
+
+Run directly:
+    python tests/test_add_messages_benchmark.py
+
+Or via pytest (correctness only, numbers printed to stdout):
+    pytest tests/test_add_messages_benchmark.py -s -v
+"""
+
+import statistics
+import time
+import tracemalloc
+import uuid
+from typing import cast
+
+from langchain_core.messages import (
+    AIMessage,
+    BaseMessage,
+    BaseMessageChunk,
+    HumanMessage,
+    RemoveMessage,
+    convert_to_messages,
+    message_chunk_to_message,
+)
+
+from langgraph.graph.message import REMOVE_ALL_MESSAGES
+
+# ── original implementation (pre-optimisation) ────────────────────────────────
+
+
+def _add_messages_original(left, right):
+    remove_all_idx = None
+    if not isinstance(left, list):
+        left = [left]
+    if not isinstance(right, list):
+        right = [right]
+    left = [
+        message_chunk_to_message(cast(BaseMessageChunk, m))
+        for m in convert_to_messages(left)
+    ]
+    right = [
+        message_chunk_to_message(cast(BaseMessageChunk, m))
+        for m in convert_to_messages(right)
+    ]
+    for m in left:
+        if m.id is None:
+            m.id = str(uuid.uuid4())
+    for idx, m in enumerate(right):
+        if m.id is None:
+            m.id = str(uuid.uuid4())
+        if isinstance(m, RemoveMessage) and m.id == REMOVE_ALL_MESSAGES:
+            remove_all_idx = idx
+    if remove_all_idx is not None:
+        return right[remove_all_idx + 1 :]
+    merged = left.copy()
+    merged_by_id = {m.id: i for i, m in enumerate(merged)}
+    ids_to_remove = set()
+    for m in right:
+        if (existing_idx := merged_by_id.get(m.id)) is not None:
+            if isinstance(m, RemoveMessage):
+                ids_to_remove.add(m.id)
+            else:
+                ids_to_remove.discard(m.id)
+                merged[existing_idx] = m
+        else:
+            if isinstance(m, RemoveMessage):
+                raise ValueError(
+                    f"Attempting to delete a message with an ID that doesn't exist ('{m.id}')"
+                )
+            merged_by_id[m.id] = len(merged)
+            merged.append(m)
+    return [m for m in merged if m.id not in ids_to_remove]
+
+
+# ── optimised implementation ──────────────────────────────────────────────────
+
+
+def _add_messages_optimized(left, right):
+    if not isinstance(left, list):
+        left = [left]
+    if not isinstance(right, list):
+        right = [right]
+
+    # Optimisation 1: skip conversion + ID assignment on left when it already
+    # contains fully-resolved BaseMessage objects (the common case after the
+    # first call, since add_messages always returns list[BaseMessage] with IDs).
+    if (
+        left
+        and isinstance(left[0], BaseMessage)
+        and not isinstance(left[0], BaseMessageChunk)
+    ):
+        left = cast(list[BaseMessage], left)
+    else:
+        left = [
+            message_chunk_to_message(cast(BaseMessageChunk, m))
+            for m in convert_to_messages(left)
+        ]
+        for m in left:
+            if m.id is None:
+                m.id = str(uuid.uuid4())
+
+    # always normalise right — it's fresh external input
+    right = [
+        message_chunk_to_message(cast(BaseMessageChunk, m))
+        for m in convert_to_messages(right)
+    ]
+    remove_all_idx = None
+    has_remove = False
+    for idx, m in enumerate(right):
+        if m.id is None:
+            m.id = str(uuid.uuid4())
+        if isinstance(m, RemoveMessage):
+            has_remove = True
+            if m.id == REMOVE_ALL_MESSAGES:
+                remove_all_idx = idx
+
+    if remove_all_idx is not None:
+        return right[remove_all_idx + 1 :]
+
+    # Optimisation 2: pure-append fast path — no removals and no ID overlaps.
+    # Builds one set over left instead of copying left + building a full dict.
+    if not has_remove:
+        left_ids = {m.id for m in left}
+        if not any(m.id in left_ids for m in right):
+            return left + right
+
+    # slow path: updates or removals present — full indexed merge
+    merged = left.copy()
+    merged_by_id = {m.id: i for i, m in enumerate(merged)}
+    ids_to_remove = set()
+    for m in right:
+        if (existing_idx := merged_by_id.get(m.id)) is not None:
+            if isinstance(m, RemoveMessage):
+                ids_to_remove.add(m.id)
+            else:
+                ids_to_remove.discard(m.id)
+                merged[existing_idx] = m
+        else:
+            if isinstance(m, RemoveMessage):
+                raise ValueError(
+                    f"Attempting to delete a message with an ID that doesn't exist ('{m.id}')"
+                )
+            merged_by_id[m.id] = len(merged)
+            merged.append(m)
+    return [m for m in merged if m.id not in ids_to_remove]
+
+
+# ── helpers ───────────────────────────────────────────────────────────────────
+
+
+def _make_messages(n: int) -> list[BaseMessage]:
+    return [
+        (HumanMessage if i % 2 == 0 else AIMessage)(
+            content=f"message {i}", id=str(uuid.uuid4())
+        )
+        for i in range(n)
+    ]
+
+
+def _bench_time(fn, left, right, *, iters: int = 2_000) -> float:
+    """Return median latency in microseconds."""
+    for _ in range(100):
+        fn(list(left), list(right))
+    times = []
+    for _ in range(iters):
+        left_copy, right_copy = list(left), list(right)
+        t0 = time.perf_counter()
+        fn(left_copy, right_copy)
+        times.append(time.perf_counter() - t0)
+    return statistics.median(times) * 1e6
+
+
+def _bench_memory(fn, left, right) -> int:
+    """Return peak memory allocated during a single call (bytes)."""
+    # one warm-up so any lazy init is excluded
+    fn(list(left), list(right))
+    left_copy, right_copy = list(left), list(right)
+    tracemalloc.start()
+    tracemalloc.clear_traces()
+    fn(left_copy, right_copy)
+    _, peak = tracemalloc.get_traced_memory()
+    tracemalloc.stop()
+    return peak
+
+
+# ── scenarios ─────────────────────────────────────────────────────────────────
+
+SCENARIOS = [
+    ("pure append  1 → 1  msg", 1, 1, "append"),
+    ("pure append  10 → 1  msg", 10, 1, "append"),
+    ("pure append  100 → 1  msg", 100, 1, "append"),
+    ("pure append  1000 → 1  msg", 1000, 1, "append"),
+    ("pure append  1000 → 5  msgs", 1000, 5, "append"),
+    ("update existing  100 → 1  msg", 100, 1, "update"),
+    ("remove message  100 → 1  msg", 100, 1, "remove"),
+]
+
+
+def _make_inputs(n_left, n_right, mode):
+    left = _make_messages(n_left)
+    right = _make_messages(n_right)
+    if mode == "update":
+        right[0] = AIMessage(content="updated", id=left[0].id)
+    elif mode == "remove":
+        right = [RemoveMessage(id=left[0].id)]
+    return left, right
+
+
+# ── main output ───────────────────────────────────────────────────────────────
+
+COL = 36
+
+
+def run_benchmarks() -> None:
+    print()
+    print("=" * 88)
+    print("add_messages benchmark — time (µs, median of 2 000 iterations)")
+    print("=" * 88)
+    print(f"{'Scenario':<{COL}} {'Original':>10} {'Optimized':>11} {'Speedup':>8}")
+    print("-" * 88)
+
+    for label, n_left, n_right, mode in SCENARIOS:
+        left, right = _make_inputs(n_left, n_right, mode)
+        t_orig = _bench_time(_add_messages_original, left, right)
+        t_opt = _bench_time(_add_messages_optimized, left, right)
+        print(f"{label:<{COL}} {t_orig:>10.2f} {t_opt:>11.2f} {t_orig / t_opt:>7.2f}x")
+
+    print()
+    print("=" * 88)
+    print("add_messages benchmark — peak memory allocated per call (bytes)")
+    print("=" * 88)
+    print(f"{'Scenario':<{COL}} {'Original':>10} {'Optimized':>11} {'Reduction':>10}")
+    print("-" * 88)
+
+    for label, n_left, n_right, mode in SCENARIOS:
+        left, right = _make_inputs(n_left, n_right, mode)
+        m_orig = _bench_memory(_add_messages_original, left, right)
+        m_opt = _bench_memory(_add_messages_optimized, left, right)
+        reduction = (1 - m_opt / m_orig) * 100 if m_orig else 0.0
+        print(f"{label:<{COL}} {m_orig:>10,} {m_opt:>11,} {reduction:>9.1f}%")
+
+    print()
+    print("=" * 88)
+    print("Simulated long thread — 200 steps × 2 msgs appended per step")
+    print("=" * 88)
+    for name, fn in [
+        ("original", _add_messages_original),
+        ("optimized", _add_messages_optimized),
+    ]:
+        state: list = []
+        t0 = time.perf_counter()
+        for step in range(200):
+            new_msgs = [
+                HumanMessage(content=f"step {step} human", id=str(uuid.uuid4())),
+                AIMessage(content=f"step {step} ai", id=str(uuid.uuid4())),
+            ]
+            state = fn(state, new_msgs)
+        elapsed = (time.perf_counter() - t0) * 1_000
+        print(f"  {name:<12}  {elapsed:.2f} ms  ({len(state)} messages)")
+    print()
+
+
+# ── pytest entry-points ───────────────────────────────────────────────────────
+
+
+def test_add_messages_correctness():
+    """Optimised implementation must match original output for every scenario."""
+    for label, n_left, n_right, mode in SCENARIOS:
+        left, right = _make_inputs(n_left, n_right, mode)
+        expected = _add_messages_original(list(left), list(right))
+        actual = _add_messages_optimized(list(left), list(right))
+        assert len(actual) == len(expected), f"[{label}] length mismatch"
+        for a, b in zip(actual, expected):
+            assert type(a) is type(b), f"[{label}] type mismatch"
+            assert a.id == b.id, f"[{label}] id mismatch"
+            assert a.content == b.content, f"[{label}] content mismatch"
+
+
+def test_add_messages_benchmark(capsys):
+    run_benchmarks()
+    out = capsys.readouterr().out
+    assert "Speedup" in out
+    assert "Optimized" in out
+
+
+if __name__ == "__main__":
+    run_benchmarks()

libs/langgraph/tests/test_messages_state.py

@@ -5,6 +5,7 @@ import langchain_core
 import pytest
 from langchain_core.messages import (
     AIMessage,
+    AIMessageChunk,
     AnyMessage,
     HumanMessage,
     RemoveMessage,
@@ -338,6 +339,123 @@ def test_remove_all_messages():
     ]
 
 
+def test_fast_path_preserves_format_openai():
+    """Pure-append fast path must still apply the `langchain-openai` formatter."""
+    left = [HumanMessage(content="prior", id="1")]
+    right = [
+        AIMessage(
+            content=[
+                {
+                    "type": "tool_use",
+                    "name": "foo",
+                    "input": {"bar": "baz"},
+                    "id": "t1",
+                }
+            ],
+            id="2",
+        )
+    ]
+    result = add_messages(left, right, format="langchain-openai")
+    assert isinstance(result[0], HumanMessage)
+    assert result[0].content == "prior"
+    assert isinstance(result[1], AIMessage)
+    # formatter collapses the tool_use content block into `tool_calls`
+    assert result[1].content == ""
+    assert len(result[1].tool_calls) == 1
+    assert result[1].tool_calls[0]["name"] == "foo"
+    assert result[1].tool_calls[0]["args"] == {"bar": "baz"}
+    assert result[1].tool_calls[0]["id"] == "t1"
+
+
+def test_fast_path_rejects_invalid_format():
+    """Pure-append fast path must validate the `format` arg like the slow path."""
+    left = [HumanMessage(content="prior", id="1")]
+    right = [AIMessage(content="new", id="2")]
+    with pytest.raises(ValueError, match="Unrecognized format="):
+        add_messages(left, right, format="bogus")  # type: ignore[arg-type]
+
+
+def test_left_starting_with_chunk_is_normalized():
+    """Opt-1 guard: a `BaseMessageChunk` at left[0] must trigger full conversion."""
+    chunk = AIMessageChunk(content="chunk", id="c1")
+    result = add_messages([chunk], [HumanMessage(content="h", id="h1")])
+    assert len(result) == 2
+    # chunk must be converted to a non-chunk message
+    assert type(result[0]).__name__ == "AIMessage"
+    assert result[0].id == "c1"
+    assert result[1].id == "h1"
+
+
+def test_left_as_dicts_is_normalized():
+    """Opt-1 guard: dicts at left[0] must trigger full conversion."""
+    left = [{"role": "user", "content": "hi", "id": "d1"}]
+    right = [AIMessage(content="reply", id="a1")]
+    result = add_messages(left, right)
+    assert len(result) == 2
+    assert isinstance(result[0], HumanMessage)
+    assert result[0].id == "d1"
+    assert result[0].content == "hi"
+
+
+def test_left_as_tuples_is_normalized():
+    """Opt-1 guard: tuple-form messages must trigger full conversion."""
+    left = [("user", "hi")]
+    right = [AIMessage(content="reply", id="a1")]
+    result = add_messages(left, right)
+    assert len(result) == 2
+    assert isinstance(result[0], HumanMessage)
+    # id is auto-assigned
+    assert isinstance(result[0].id, str) and UUID(result[0].id, version=4)
+
+
+def test_left_first_msg_missing_id_is_normalized():
+    """Opt-1 guard: a BaseMessage without an id at left[0] falls to the else branch."""
+    left = [HumanMessage(content="hi")]  # no id
+    right = [AIMessage(content="reply", id="a1")]
+    result = add_messages(left, right)
+    assert len(result) == 2
+    # left's id must have been auto-assigned
+    assert isinstance(result[0].id, str) and UUID(result[0].id, version=4)
+
+
+def test_duplicate_ids_in_right_with_nonempty_left():
+    """Opt-2 guard: intra-right duplicate ids must take slow path (dedup kept)."""
+    left = [HumanMessage(content="prior", id="1")]
+    right = [
+        AIMessage(content="first", id="2"),
+        AIMessage(content="second", id="2"),
+    ]
+    result = add_messages(left, right)
+    assert len(result) == 2
+    assert result[0].id == "1"
+    assert result[1].id == "2"
+    assert result[1].content == "second"
+
+
+def test_right_with_none_ids_pure_append():
+    """Fast path still correct when right entries start with id=None (fresh uuids assigned)."""
+    left = [HumanMessage(content="prior", id="1")]
+    right = [AIMessage(content="a"), AIMessage(content="b")]
+    result = add_messages(left, right)
+    assert len(result) == 3
+    assert result[0].id == "1"
+    for m in result[1:]:
+        assert isinstance(m.id, str) and UUID(m.id, version=4)
+    # fresh uuids must be distinct
+    assert result[1].id != result[2].id
+
+
+def test_fast_path_returns_fresh_list():
+    """Fast path must return a new list object (not mutate or alias left)."""
+    left = [HumanMessage(content="prior", id="1")]
+    right = [AIMessage(content="new", id="2")]
+    result = add_messages(left, right)
+    assert result is not left
+    # left must be untouched
+    assert len(left) == 1
+    assert left[0].id == "1"
+
+
 def test_push_messages_in_graph():
     class MessagesState(TypedDict):
         messages: Annotated[list[AnyMessage], add_messages]

libs/prebuilt/langgraph/prebuilt/tool_node.py

@@ -82,6 +82,7 @@ from langchain_core.tools.base import (
     _is_injected_arg_type,
     get_all_basemodel_annotations,
 )
+from langgraph._internal._constants import CONF, CONFIG_KEY_READ
 from langgraph._internal._runnable import RunnableCallable
 from langgraph.errors import GraphBubbleUp
 from langgraph.graph.message import REMOVE_ALL_MESSAGES
@@ -800,7 +801,7 @@ class ToolNode(RunnableCallable):
         # Construct ToolRuntime instances at the top level for each tool call
         tool_runtimes = []
         for call, cfg in zip(tool_calls, config_list, strict=False):
-            state = self._extract_state(input)
+            state = self._extract_state(input, cfg)
             tool_runtime = ToolRuntime(
                 state=state,
                 tool_call_id=call["id"],
@@ -835,7 +836,7 @@ class ToolNode(RunnableCallable):
         # Construct ToolRuntime instances at the top level for each tool call
         tool_runtimes = []
         for call, cfg in zip(tool_calls, config_list, strict=False):
-            state = self._extract_state(input)
+            state = self._extract_state(input, cfg)
             tool_runtime = ToolRuntime(
                 state=state,
                 tool_call_id=call["id"],
@@ -1273,18 +1274,37 @@ class ToolNode(RunnableCallable):
         return None
 
     def _extract_state(
-        self, input: list[AnyMessage] | dict[str, Any] | BaseModel
+        self,
+        input: list[AnyMessage] | dict[str, Any] | BaseModel,
+        config: RunnableConfig,
     ) -> list[AnyMessage] | dict[str, Any] | BaseModel:
-        """Extract state from input, handling ToolCallWithContext if present.
+        """Extract state from input.
 
-        Args:
-            input: The input which may be raw state or ToolCallWithContext.
+        Three input shapes:
 
-        Returns:
-            The actual state to pass to wrap_tool_call wrappers.
+        - `ToolCallWithContext` dict — legacy Send payload carrying an inlined
+          state snapshot; return `input["state"]`.
+        - list of `ToolCall` dicts — new Send payload with no inlined state;
+          hydrate state from channels via `CONFIG_KEY_READ`.
+        - regular graph state (dict/list/BaseModel) — return `input` as-is.
         """
         if isinstance(input, dict) and input.get("__type") == "tool_call_with_context":
             return input["state"]
+        if (
+            isinstance(input, list)
+            and input
+            and isinstance(input[-1], dict)
+            and input[-1].get("type") == "tool_call"
+        ):
+            read = config.get(CONF, {}).get(CONFIG_KEY_READ)
+            if read is None:
+                return {}
+            # Pregel installs CONFIG_KEY_READ as
+            # `functools.partial(local_read, scratchpad, channels, managed, task)`.
+            # Match the previous inlined-state contract by reading channels only;
+            # managed values have their own injection path (`ToolRuntime.context`).
+            channels = read.args[1]
+            return cast("dict[str, Any]", read(list(channels), False))
         return input
 
     def _inject_tool_args(

libs/prebuilt/tests/test_on_tool_call.py

@@ -1320,6 +1320,98 @@ async def test_state_extraction_with_tool_call_with_context_async() -> None:
     assert "tool_call" not in state_seen[0]
 
 
+def _config_with_channel_read(
+    channel_values: dict[str, object],
+    store: BaseStore | None = None,
+) -> RunnableConfig:
+    """Build a config that mimics `CONFIG_KEY_READ` as Pregel installs it.
+
+    Pregel always installs a `functools.partial(local_read, scratchpad,
+    channels, managed, task)`, and `ToolNode` introspects that partial to
+    learn channel names. The stub matches the shape: partial whose second and
+    third positional args are `channels` and `managed` mappings.
+    """
+    import functools
+
+    channels_stub = {k: None for k in channel_values}
+    managed_stub: dict[str, object] = {}
+
+    # Shape matches pregel's real partial:
+    # functools.partial(local_read, scratchpad, channels, managed, task)
+    def _read(scratchpad, channels, managed, task, select, fresh):  # noqa: ARG001
+        if isinstance(select, str):
+            return channel_values[select]
+        return {k: channel_values[k] for k in select if k in channel_values}
+
+    read = functools.partial(_read, None, channels_stub, managed_stub, None)
+    cfg = _create_config_with_runtime(store)
+    cfg["configurable"]["__pregel_read"] = read
+    return cfg
+
+
+def test_list_form_send_hydrates_state_from_channel_read() -> None:
+    """Send('tools', [tool_call]) with no inlined state should hydrate
+    ToolRuntime.state from CONFIG_KEY_READ (full state read)."""
+    state_seen = []
+
+    def state_inspector_handler(
+        request: ToolCallRequest,
+        execute: Callable[[ToolCallRequest], ToolMessage | Command],
+    ) -> ToolMessage | Command:
+        state_seen.append(request.state)
+        return execute(request)
+
+    channel_values = {
+        "messages": [AIMessage("from channels")],
+        "files": {"/a.md": "body"},
+    }
+
+    tool_node = ToolNode([add], wrap_tool_call=state_inspector_handler)
+
+    tool_call: ToolCall = {
+        "name": "add",
+        "args": {"a": 1, "b": 2},
+        "id": "call_1",
+        "type": "tool_call",
+    }
+
+    tool_node.invoke([tool_call], config=_config_with_channel_read(channel_values))
+
+    assert len(state_seen) == 1
+    got = state_seen[0]
+    assert got == channel_values
+    assert "messages" in got and "files" in got
+
+
+async def test_list_form_send_hydrates_state_async() -> None:
+    state_seen = []
+
+    def state_inspector_handler(
+        request: ToolCallRequest,
+        execute: Callable[[ToolCallRequest], ToolMessage | Command],
+    ) -> ToolMessage | Command:
+        state_seen.append(request.state)
+        return execute(request)
+
+    channel_values = {"messages": [AIMessage("from channels")], "files": {}}
+
+    tool_node = ToolNode([add], wrap_tool_call=state_inspector_handler)
+
+    tool_call: ToolCall = {
+        "name": "add",
+        "args": {"a": 1, "b": 2},
+        "id": "call_1",
+        "type": "tool_call",
+    }
+
+    await tool_node.ainvoke(
+        [tool_call], config=_config_with_channel_read(channel_values)
+    )
+
+    assert len(state_seen) == 1
+    assert state_seen[0] == channel_values
+
+
 def test_tool_call_request_is_frozen() -> None:
     """Test that ToolCallRequest raises deprecation warnings on direct attribute reassignment."""
     tool_call: ToolCall = {"name": "add", "args": {"a": 1, "b": 2}, "id": "call_1"}