diff --git a/src/dedalus_labs/lib/runner/core.py b/src/dedalus_labs/lib/runner/core.py
index 94f0acf..0e44600 100644
--- a/src/dedalus_labs/lib/runner/core.py
+++ b/src/dedalus_labs/lib/runner/core.py
@@ -8,6 +8,7 @@
 
 import asyncio
 import inspect
+import json
 from typing import (
     TYPE_CHECKING,
     Any,
@@ -685,6 +686,7 @@ async def _execute_streaming_async(
             content_chunks = 0
             tool_call_chunks = 0
             finish_reason = None
+            mcp_tool_results_from_server: list = []
             async for chunk in stream:
                 chunk_count += 1
                 if exec_config.verbose:
@@ -694,6 +696,12 @@ async def _execute_streaming_async(
                         meta = extra.get("x_dedalus_event") or extra.get("dedalus_event")
                         if isinstance(meta, dict) and meta.get("type") == "agent_updated":
                             print(f" [EVENT] agent_updated: agent={meta.get('agent')} model={meta.get('model')}")
+
+                # Collect MCP tool results emitted by the server
+                chunk_extra = getattr(chunk, "__pydantic_extra__", None) or {}
+                if isinstance(chunk_extra, dict) and "mcp_tool_results" in chunk_extra:
+                    mcp_tool_results_from_server = chunk_extra["mcp_tool_results"]
+
                 if hasattr(chunk, "choices") and chunk.choices:
                     choice = chunk.choices[0]
                     delta = choice.delta
@@ -765,7 +773,6 @@ async def _execute_streaming_async(
                     local_only = [
                         tc for tc in tool_calls if tc["function"]["name"] in getattr(tool_handler, "_funcs", {})
                     ]
-                    messages.append({"role": "assistant", "tool_calls": local_only})
 
                     from ._scheduler import execute_local_tools_async
 
@@ -965,9 +972,16 @@ def _execute_streaming_sync(
             tool_call_chunks = 0
             finish_reason = None
             accumulated_content = ""
+            mcp_tool_results_from_server: list = []
 
             for chunk in stream:
                 chunk_count += 1
+
+                # Collect MCP tool results emitted by the server
+                chunk_extra = getattr(chunk, "__pydantic_extra__", None) or {}
+                if isinstance(chunk_extra, dict) and "mcp_tool_results" in chunk_extra:
+                    mcp_tool_results_from_server = chunk_extra["mcp_tool_results"]
+
                 if hasattr(chunk, "choices") and chunk.choices:
                     choice = chunk.choices[0]
                     delta = choice.delta
@@ -1048,7 +1062,6 @@ def _execute_streaming_sync(
                     local_only = [
                         tc for tc in tool_calls if tc["function"]["name"] in getattr(tool_handler, "_funcs", {})
                     ]
-                    messages.append({"role": "assistant", "tool_calls": local_only})
 
                     from ._scheduler import execute_local_tools_sync
 
@@ -1153,16 +1166,18 @@ def _extract_tool_calls(self, choice) -> list[ToolCall]:
             fn = tc_dict.get("function", {})
             fn_dict = vars(fn) if hasattr(fn, "__dict__") else fn
 
-            calls.append(
-                {
-                    "id": tc_dict.get("id", ""),
-                    "type": tc_dict.get("type", "function"),
-                    "function": {
-                        "name": fn_dict.get("name", ""),
-                        "arguments": fn_dict.get("arguments", "{}"),
-                    },
-                }
-            )
+            tc_out: ToolCall = {
+                "id": tc_dict.get("id", ""),
+                "type": tc_dict.get("type", "function"),
+                "function": {
+                    "name": fn_dict.get("name", ""),
+                    "arguments": fn_dict.get("arguments", "{}"),
+                },
+            }
+            thought_sig = tc_dict.get("thought_signature")
+            if thought_sig:
+                tc_out["thought_signature"] = thought_sig
+            calls.append(tc_out)
         return calls
 
     async def _execute_tool_calls(
@@ -1245,6 +1260,9 @@ def _accumulate_tool_calls(self, deltas, acc: list[ToolCall]) -> None:
                     acc[index]["function"]["name"] = fn.name
                 if hasattr(fn, "arguments") and fn.arguments:
                     acc[index]["function"]["arguments"] += fn.arguments
+            thought_sig = getattr(delta, "thought_signature", None)
+            if thought_sig:
+                acc[index]["thought_signature"] = thought_sig
 
     @staticmethod
     def _mk_kwargs(mc: _ModelConfig) -> Dict[str, Any]: