core/agent: keep a Messages round's provider blocks on the assistant message

DeepSeek's Anthropic compat answers a hosted search inside the turn: the response carries the `thinking` that picked the query, the `server_tool_use`, and the `web_search_tool_result`. The response mapping kept text and tool_use only, so the round lost its evidence — and the `thinking` signature, which only the provider can verify, could not go back at all. `AssistantChatMessage.provider_blocks` carries those blocks as raw JSON now (`thinking` text *and* signature, the query, the result entries with an `encrypted_content` the API rejects when trimmed) and the assistant turn hands them back first, ahead of its text and tool_use blocks; `thinking` also lands in `reasoning_content`, so the chain of thought streams as reasoning like every other surface's.

`AnthropicRawContentBlock` names the provider fields a streamed block carries, and `AnthropicServerToolUseContent` keeps the `caller` metadata the wire sends.

src/plyngent/agent/messages_bridge.py

@@ -18,15 +18,17 @@ from plyngent.lmproto.anthropic.model import (
     AnthropicMessageResponse,
     AnthropicMessagesParam,
     AnthropicResponseText,
-    AnthropicResponseToolUse,
+    AnthropicServerToolUseContent,
     AnthropicTextContent,
     AnthropicThinkingConfig,
+    AnthropicThinkingContent,
     AnthropicToolChoice,
     AnthropicToolDefinition,
     AnthropicToolResultContent,
     AnthropicToolUseContent,
     AnthropicUsage,
     AnthropicUserMessage,
+    AnthropicWebSearchToolResultContent,
 )
 from plyngent.lmproto.openai_compatible.model import (
     AnyAssistantToolCall,
@@ -133,7 +135,16 @@ def _tool_choice_from_chat(param: ChatCompletionsParam) -> AnthropicToolChoice |
 
 
 def _assistant_to_anthropic(message: AssistantChatMessage) -> AnthropicAssistantMessage | None:
-    blocks: list[AnthropicTextContent | AnthropicToolUseContent] = []
+    """The assistant turn for the wire: opaque blocks, then text, then calls.
+
+    ``provider_blocks`` go back first and verbatim (a ``thinking`` block's
+    signature is only the provider's to verify, and a hosted search's
+    ``web_search_tool_result`` entries carry an ``encrypted_content`` the API
+    rejects when trimmed), which is also the order the API sends them in.
+    """
+    blocks: list[AnthropicTextContent | AnthropicToolUseContent | dict[str, Any]] = []
+    if message.provider_blocks is not UNSET and message.provider_blocks:
+        blocks.extend(message.provider_blocks)
     if isinstance(message.content, str) and message.content:
         blocks.append(AnthropicTextContent(text=message.content))
     if message.tool_calls is not UNSET and message.tool_calls:
@@ -219,22 +230,59 @@ def chat_messages_to_anthropic(  # noqa: C901 — multi-role conversion
     return system, out
 
 
+def _thinking_block_json(block: AnthropicThinkingContent) -> dict[str, Any]:
+    """A ``thinking`` block as JSON: its text, plus the signature when sent."""
+    out: dict[str, Any] = {"type": "thinking", "thinking": block.thinking}
+    if isinstance(block.signature, str):
+        out["signature"] = block.signature
+    return out
+
+
+def _server_block_json(
+    block: AnthropicServerToolUseContent | AnthropicWebSearchToolResultContent,
+) -> dict[str, Any]:
+    """A hosted search's block as JSON: the query it ran, or the raw entries.
+
+    Rebuilt from the parsed block: an ``encrypted_content`` (and any other key
+    inside the loose ``content`` entries) survives byte for byte, while a key
+    the block model does not name cannot come back.
+    """
+    if isinstance(block, AnthropicServerToolUseContent):
+        out: dict[str, Any] = {"type": "server_tool_use", "id": block.id, "name": block.name, "input": block.input}
+        if block.caller is not UNSET:
+            out["caller"] = block.caller
+        return out
+    return {"type": "web_search_tool_result", "tool_use_id": block.tool_use_id, "content": block.content}
+
+
 def anthropic_response_to_assistant(response: AnthropicMessageResponse) -> AssistantChatMessage:
     """Map a completed Anthropic message to agent ``AssistantChatMessage``.
 
-    Server-side blocks (``server_tool_use`` / ``web_search_tool_result``) and
+    ``thinking`` lands in ``reasoning_content`` (the chat-shaped slot every
-    ``thinking`` are not part of the chat-shaped message: a search the model ran
+    surface's chain-of-thought goes into) and, signature included, in
-    through its backend already shows up in the text it answered with.
+    ``provider_blocks`` — the API wants the block back to continue a turn it
+    reasoned through. A hosted search's ``server_tool_use`` +
+    ``web_search_tool_result`` pair is not a call for the local registry, but it
+    is the model's own evidence: both go into ``provider_blocks`` verbatim, so
+    the next request hands them back and the model does not search again.
     """
     text_parts: list[str] = []
+    thinking_parts: list[str] = []
+    provider_blocks: list[dict[str, Any]] = []
     tool_calls: list[AnyAssistantToolCall] = []
     for block in response.content:
         if isinstance(block, AnthropicResponseText):
             if block.text:
                 text_parts.append(block.text)
             continue
-        if not isinstance(block, AnthropicResponseToolUse):
+        if isinstance(block, AnthropicThinkingContent):
+            thinking_parts.append(block.thinking)
+            provider_blocks.append(_thinking_block_json(block))
             continue
+        if isinstance(block, (AnthropicServerToolUseContent, AnthropicWebSearchToolResultContent)):
+            provider_blocks.append(_server_block_json(block))
+            continue
+        # The union's remaining member is the local tool call.
         tool_calls.append(
             AssistantFunctionToolCall(
                 id=block.id,
@@ -248,6 +296,8 @@ def anthropic_response_to_assistant(response: AnthropicMessageResponse) -> Assis
     return AssistantChatMessage(
         content=text or None,
         tool_calls=tool_calls or UNSET,
+        reasoning_content="".join(thinking_parts) or UNSET,
+        provider_blocks=provider_blocks or UNSET,
     )
 
 

src/plyngent/agent/stream_chunks.py

@@ -79,6 +79,32 @@ def reasoning_delta_chunk(
     )
 
 
+def provider_blocks_chunk(
+    *,
+    model: str,
+    blocks: list[dict[str, Any]],
+    created: int = 0,
+) -> ChatCompletionChunk:
+    """Carry provider-opaque blocks a bridge rebuilt mid-stream.
+
+    The loop copies them onto the round's assistant message
+    (``AssistantChatMessage.provider_blocks``), which is what puts them back on
+    the wire for the surface that produced them.
+    """
+    return ChatCompletionChunk(
+        id="bridge-stream",
+        object="chat.completion.chunk",
+        created=created,
+        model=model,
+        choices=[
+            ChunkChoice(
+                index=0,
+                delta=DeltaMessage(provider_blocks=blocks),
+            )
+        ],
+    )
+
+
 def tool_call_delta_chunk(
     *,
     model: str,
@@ -127,6 +153,7 @@ def usage_chunk(*, model: str, usage: dict[str, Any], created: int = 0) -> ChatC
 
 __all__ = [
     "finish_reason_chunk",
+    "provider_blocks_chunk",
     "reasoning_delta_chunk",
     "text_delta_chunk",
     "tool_call_delta_chunk",

src/plyngent/lmproto/anthropic/model.py

@@ -39,7 +39,11 @@ class AnthropicUserMessage(Struct, tag_field="role", tag="user"):
 
 
 class AnthropicAssistantMessage(Struct, tag_field="role", tag="assistant"):
-    content: str | list[AnthropicTextContent | AnthropicToolUseContent]
+    # ``dict`` entries are provider-opaque blocks echoed back verbatim: a
+    # ``thinking`` block (its ``signature`` cannot be rebuilt from the text) and
+    # the ``server_tool_use`` + ``web_search_tool_result`` pair a hosted search
+    # answers inside the turn.
+    content: str | list[AnthropicTextContent | AnthropicToolUseContent | dict[str, Any]]
 
 
 type AnthropicMessage = AnthropicUserMessage | AnthropicAssistantMessage
@@ -125,11 +129,13 @@ class AnthropicServerToolUseContent(Struct, omit_defaults=True, tag_field="type"
     Not a call for the local registry: the matching
     :class:`AnthropicWebSearchToolResultContent` arrives in the same response
     (see the ``messages_dispatch`` / ``messages_bridge`` bullets in AGENTS.md).
+    ``caller`` is the surface's own metadata and goes back with the block.
     """
 
     id: str = ""
     name: str = ""
     input: dict[str, Any] = field(default_factory=dict)
+    caller: dict[str, Any] | Unset = UNSET
 
 
 class AnthropicWebSearchToolResultContent(Struct, omit_defaults=True, tag_field="type", tag="web_search_tool_result"):
@@ -166,12 +172,27 @@ class AnthropicMessageResponse(Struct, omit_defaults=True):
 
 
 class AnthropicRawContentBlock(Struct, omit_defaults=True):
+    """One streamed content block: the ``content_block`` / ``delta`` payload.
+
+    The fields cover the response union: ``text`` fragments, ``thinking`` and
+    its opaque ``signature``, a ``server_tool_use``'s ``input`` (streamed as
+    ``partial_json``), and a ``web_search_tool_result``'s ``tool_use_id`` +
+    ``content`` (kept loose — an entry's ``encrypted_content`` goes back
+    unchanged). ``agent.messages_dispatch`` rebuilds the blocks from these to
+    hand them to the next request.
+    """
+
     type: str = ""
     id: str | None = None
     name: str | None = None
     text: str | None = None
     input: dict[str, Any] | None = None
     partial_json: str | None = None
+    thinking: str | None = None
+    signature: str | None = None
+    tool_use_id: str | None = None
+    content: list[dict[str, Any]] | None = None
+    caller: dict[str, Any] | None = None
 
 
 class AnthropicMessageStart(Struct, tag_field="type", tag="message_start"):

src/plyngent/lmproto/openai_compatible/model.py

@@ -74,6 +74,12 @@ class AssistantChatMessage(Struct, tag_field="role", tag="assistant"):
     tool_calls: list[AnyAssistantToolCall] | Unset = UNSET
     # OpenAI-compat / DeepSeek thinking streams (omitted when unset).
     reasoning_content: str | Unset = UNSET
+    # Provider-opaque assistant blocks kept as raw JSON and echoed back verbatim
+    # by the surface that produced them (Anthropic: a ``thinking`` block, whose
+    # ``signature`` only the provider can verify, and the ``server_tool_use`` +
+    # ``web_search_tool_result`` pair a hosted search answers inside the turn).
+    # Surfaces that do not know them send the message without the field.
+    provider_blocks: list[dict[str, Any]] | Unset = UNSET
 
 
 class ToolChatMessage(ChatMessage, tag_field="role", tag="tool"):
@@ -243,6 +249,10 @@ class DeltaMessage(Struct):
     # ``response.reasoning_text.done``), replacing any streamed fragments.
     reasoning_full: bool | Unset = UNSET
     tool_calls: list[StreamToolCallDelta] | Unset = UNSET
+    # Provider-opaque blocks a bridge rebuilt mid-stream (see
+    # ``AssistantChatMessage.provider_blocks``): the loop copies them onto the
+    # round's assistant message.
+    provider_blocks: list[dict[str, Any]] | Unset = UNSET
 
 
 class ChunkChoice(Struct):

tests/test_agent/test_messages_bridge.py

@@ -4,6 +4,7 @@ from __future__ import annotations
 
 from typing import TYPE_CHECKING
 
+import msgspec
 from msgspec import UNSET
 
 from plyngent.agent.messages_bridge import (
@@ -156,15 +157,20 @@ def test_anthropic_response_to_assistant_with_tools() -> None:
     assert '"a":1' in call.function.arguments or '"a": 1' in call.function.arguments
 
 
-def test_anthropic_response_to_assistant_ignores_server_tool_blocks() -> None:
+def test_anthropic_response_to_assistant_keeps_thinking_and_search_blocks() -> None:
-    """A server-side search is not a call for the registry, nor part of the message."""
+    """A server-side search is not a registry call, but it is the round's evidence."""
     response = AnthropicMessageResponse(
         id="msg_search",
         model="deepseek-flash",
         stop_reason="end_turn",
         content=[
             AnthropicThinkingContent(thinking="Let me search.", signature="sig-1"),
-            AnthropicServerToolUseContent(id="call_00_1", name="web_search", input={"query": "DeepSeek-V4"}),
+            AnthropicServerToolUseContent(
+                id="call_00_1",
+                name="web_search",
+                input={"query": "DeepSeek-V4"},
+                caller={"type": "direct"},
+            ),
             AnthropicWebSearchToolResultContent(
                 tool_use_id="call_00_1",
                 content=[{"type": "web_search_result", "url": "https://api-docs.deepseek.com"}],
@@ -176,6 +182,65 @@ def test_anthropic_response_to_assistant_ignores_server_tool_blocks() -> None:
     assistant = anthropic_response_to_assistant(response)
     assert assistant.content == "DeepSeek-V4 is out."
     assert assistant.tool_calls is UNSET
+    # The chain of thought is the round's reasoning text; the signature it must
+    # go back with only exists on the block.
+    assert assistant.reasoning_content == "Let me search."
+    assert assistant.provider_blocks == [
+        {"type": "thinking", "thinking": "Let me search.", "signature": "sig-1"},
+        {
+            "type": "server_tool_use",
+            "id": "call_00_1",
+            "name": "web_search",
+            "input": {"query": "DeepSeek-V4"},
+            "caller": {"type": "direct"},
+        },
+        {
+            "type": "web_search_tool_result",
+            "tool_use_id": "call_00_1",
+            "content": [{"type": "web_search_result", "url": "https://api-docs.deepseek.com"}],
+        },
+    ]
+
+
+def test_chat_param_to_anthropic_param_hands_provider_blocks_back() -> None:
+    """The next request carries the round's thinking and search blocks first."""
+    assistant = AssistantChatMessage(
+        content="DeepSeek-V4 is out.",
+        reasoning_content="Let me search.",
+        provider_blocks=[
+            {"type": "thinking", "thinking": "Let me search.", "signature": "sig-1"},
+            {
+                "type": "web_search_tool_result",
+                "tool_use_id": "call_00_1",
+                "content": [{"type": "web_search_result", "encrypted_content": "sd918tZXSvVp"}],
+            },
+        ],
+        tool_calls=[
+            AssistantFunctionToolCall(
+                id="tu_1",
+                function=AssistantFunctionTool(name="read_file", arguments='{"path": "a.py"}'),
+            )
+        ],
+    )
+    param = ChatCompletionsParam(model="deepseek-flash", messages=[assistant])
+    built = chat_param_to_anthropic_param(param)
+    # The wire shape: DeepSeek answers a trimmed ``encrypted_content`` with 422.
+    data = msgspec.json.decode(msgspec.json.encode(built))
+    assert data["messages"] == [
+        {
+            "role": "assistant",
+            "content": [
+                {"type": "thinking", "thinking": "Let me search.", "signature": "sig-1"},
+                {
+                    "type": "web_search_tool_result",
+                    "tool_use_id": "call_00_1",
+                    "content": [{"type": "web_search_result", "encrypted_content": "sd918tZXSvVp"}],
+                },
+                {"type": "text", "text": "DeepSeek-V4 is out."},
+                {"type": "tool_use", "id": "tu_1", "name": "read_file", "input": {"path": "a.py"}},
+            ],
+        }
+    ]
 
 
 def test_provider_tools_to_anthropic_tools_maps_the_search_intent() -> None:

tests/test_lmproto/test_anthropic.py

@@ -6,11 +6,14 @@ import pytest
 from plyngent.lmproto.anthropic import AnthropicClient
 from plyngent.lmproto.anthropic.config import AnthropicConfig
 from plyngent.lmproto.anthropic.model import (
+    AnthropicAssistantMessage,
     AnthropicContentBlockDelta,
     AnthropicMessageResponse,
     AnthropicMessagesParam,
     AnthropicMessageStop,
+    AnthropicRawContentBlock,
     AnthropicResponseText,
+    AnthropicTextContent,
     AnthropicThinkingConfig,
     AnthropicUsage,
     AnthropicUserMessage,
@@ -126,6 +129,52 @@ def test_messages_param_keeps_the_thinking_type_on_the_wire() -> None:
     assert data["thinking"] == {"type": "enabled", "budget_tokens": 16384}
 
 
+def test_stream_block_keeps_the_provider_fields() -> None:
+    """A streamed block carries what a rebuild puts back on the wire."""
+    result = msgspec.json.decode(
+        b'{"type":"web_search_tool_result","tool_use_id":"call_00_1",'
+        b'"content":[{"type":"web_search_result","encrypted_content":"sd9"}]}',
+        type=AnthropicRawContentBlock,
+    )
+    assert result.tool_use_id == "call_00_1"
+    assert result.content == [{"type": "web_search_result", "encrypted_content": "sd9"}]
+    thinking = msgspec.json.decode(
+        b'{"type":"thinking","thinking":"hmm","signature":"sig-1"}',
+        type=AnthropicRawContentBlock,
+    )
+    assert (thinking.thinking, thinking.signature) == ("hmm", "sig-1")
+
+
+def test_assistant_message_encodes_provider_blocks_verbatim() -> None:
+    """An echoed block keeps its own keys — ``encrypted_content`` included."""
+    param = AnthropicMessagesParam(
+        model="deepseek-flash",
+        messages=[
+            AnthropicAssistantMessage(
+                content=[
+                    {"type": "thinking", "thinking": "hmm", "signature": "sig-1"},
+                    {
+                        "type": "web_search_tool_result",
+                        "tool_use_id": "call_00_1",
+                        "content": [{"type": "web_search_result", "encrypted_content": "sd9"}],
+                    },
+                    AnthropicTextContent(text="done"),
+                ]
+            )
+        ],
+    )
+    data = msgspec.json.decode(msgspec.json.encode(param))
+    assert data["messages"][0]["content"] == [
+        {"type": "thinking", "thinking": "hmm", "signature": "sig-1"},
+        {
+            "type": "web_search_tool_result",
+            "tool_use_id": "call_00_1",
+            "content": [{"type": "web_search_result", "encrypted_content": "sd9"}],
+        },
+        {"type": "text", "text": "done"},
+    ]
+
+
 async def test_client_messages_create(monkeypatch: pytest.MonkeyPatch) -> None:
     client = AnthropicClient(AnthropicConfig(api_key="sk-test", base_url="https://example/v1"))