diff --git a/src/acp/contrib/tool_calls.py b/src/acp/contrib/tool_calls.py
index 6fa5a7f5..3b5c05c9 100644
--- a/src/acp/contrib/tool_calls.py
+++ b/src/acp/contrib/tool_calls.py
@@ -2,6 +2,7 @@
 
 import uuid
 from collections.abc import Callable, Sequence
+from copy import deepcopy
 from typing import Any, cast
 
 from pydantic import BaseModel, ConfigDict
@@ -86,8 +87,8 @@ def __init__(
         self.status = status
         self.content = _copy_model_list(content)
         self.locations = _copy_model_list(locations)
-        self.raw_input = raw_input
-        self.raw_output = raw_output
+        self.raw_input = deepcopy(raw_input)
+        self.raw_output = deepcopy(raw_output)
         self._stream_buffer: str | None = None
 
     def to_view(self) -> TrackedToolCallView:
diff --git a/tests/contrib/test_contrib_tool_calls.py b/tests/contrib/test_contrib_tool_calls.py
index 71ffefc2..80e6f05c 100644
--- a/tests/contrib/test_contrib_tool_calls.py
+++ b/tests/contrib/test_contrib_tool_calls.py
@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import pytest
+
 from acp.contrib.tool_calls import ToolCallTracker
 from acp.schema import ContentToolCallContent, TextContentBlock, ToolCallProgress
 
@@ -33,3 +35,41 @@ def test_tool_call_tracker_streaming_text_updates_content():
     assert isinstance(second_content, ContentToolCallContent)
     assert isinstance(second_content.content, TextContentBlock)
     assert second_content.content.text == "hello, world"
+
+
+@pytest.mark.parametrize("field", ["raw_input", "raw_output"])
+def test_tracker_start_snapshots_incoming_raw_payloads(field: str) -> None:
+    tracker = ToolCallTracker()
+    payload = {"nested": ["original"]}
+    notification = tracker.start(
+        "external",
+        title="Run",
+        raw_input=payload if field == "raw_input" else None,
+        raw_output=payload if field == "raw_output" else None,
+    )
+
+    payload["nested"].append("caller mutation")
+
+    assert getattr(tracker.view("external"), field) == {"nested": ["original"]}
+    assert getattr(notification, field) == {"nested": ["original"]}
+
+
+@pytest.mark.parametrize("payload", [None, False, 0, "text", ["item"]])
+def test_tracker_preserves_json_raw_payload_values(payload: object) -> None:
+    tracker = ToolCallTracker()
+    tracker.start("external", title="Run", raw_input=payload, raw_output=payload)
+
+    assert tracker.view("external").raw_input == payload
+    assert tracker.tool_call_model("external").raw_output == payload
+
+
+def test_tracker_progress_can_clear_raw_payloads() -> None:
+    tracker = ToolCallTracker()
+    tracker.start("external", title="Run", raw_input={"old": True}, raw_output={"old": True})
+
+    progress = tracker.progress("external", raw_input=None, raw_output=None)
+
+    assert progress.raw_input is None
+    assert progress.raw_output is None
+    assert tracker.view("external").raw_input is None
+    assert tracker.view("external").raw_output is None