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fix: repair orphaned toolUse in the last session message during restore #2073

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fix: repair orphaned toolUse in the last session message during restore #2073

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73 changes: 42 additions & 31 deletions src/strands/session/repository_session_manager.py
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Original file line number Diff line number Diff line change
Expand Up @@ -273,37 +273,48 @@ def _fix_broken_tool_use(self, messages: list[Message]) -> list[Message]:

# Then check for orphaned toolUse messages
for index, message in enumerate(messages):
# Check all but the latest message in the messages array
# The latest message being orphaned is handled in the agent class
if index + 1 < len(messages):
if any("toolUse" in content for content in message["content"]):
tool_use_ids = [
content["toolUse"]["toolUseId"] for content in message["content"] if "toolUse" in content
]

# Check if there are more messages after the current toolUse message
tool_result_ids = [
content["toolResult"]["toolUseId"]
for content in messages[index + 1]["content"]
if "toolResult" in content
]

missing_tool_use_ids = list(set(tool_use_ids) - set(tool_result_ids))
# If there are missing tool use ids, that means the messages history is broken
if missing_tool_use_ids:
logger.warning(
"Session message history has an orphaned toolUse with no toolResult. "
"Adding toolResult content blocks to create valid conversation."
)
# Create the missing toolResult content blocks
missing_content_blocks = generate_missing_tool_result_content(missing_tool_use_ids)

if tool_result_ids:
# If there were any toolResult ids, that means only some of the content blocks are missing
messages[index + 1]["content"].extend(missing_content_blocks)
else:
# The message following the toolUse was not a toolResult, so lets insert it
messages.insert(index + 1, {"role": "user", "content": missing_content_blocks})
if not any("toolUse" in content for content in message["content"]):
continue

tool_use_ids = [
content["toolUse"]["toolUseId"] for content in message["content"] if "toolUse" in content
]

if index + 1 >= len(messages):
# The last message has an orphaned toolUse. The in-process fallback
# (_has_tool_use_in_latest_message) only works within the same process.
# On cross-process restore the tool execution context is lost, so report
# an error to the model and let it decide how to proceed.
logger.warning(
"Session message history ends with an orphaned toolUse with no toolResult. "
"Adding toolResult content blocks to create valid conversation."
)
missing_content_blocks = generate_missing_tool_result_content(tool_use_ids)
messages.append({"role": "user", "content": missing_content_blocks})
else:
# Check if the next message already has tool results
tool_result_ids = [
content["toolResult"]["toolUseId"]
for content in messages[index + 1]["content"]
if "toolResult" in content
]

missing_tool_use_ids = list(set(tool_use_ids) - set(tool_result_ids))
# If there are missing tool use ids, that means the messages history is broken
if missing_tool_use_ids:
logger.warning(
"Session message history has an orphaned toolUse with no toolResult. "
"Adding toolResult content blocks to create valid conversation."
)
# Create the missing toolResult content blocks
missing_content_blocks = generate_missing_tool_result_content(missing_tool_use_ids)

if tool_result_ids:
# If there were any toolResult ids, that means only some of the content blocks are missing
messages[index + 1]["content"].extend(missing_content_blocks)
else:
# The message following the toolUse was not a toolResult, so lets insert it
messages.insert(index + 1, {"role": "user", "content": missing_content_blocks})
return messages

def sync_multi_agent(self, source: "MultiAgentBase", **kwargs: Any) -> None:
Expand Down
13 changes: 9 additions & 4 deletions tests/strands/session/test_repository_session_manager.py
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Original file line number Diff line number Diff line change
Expand Up @@ -416,8 +416,8 @@ def test_fix_broken_tool_use_handles_multiple_orphaned_tools(existing_session_ma
assert tool_use_ids == {"orphaned-123", "orphaned-456"}


def test_fix_broken_tool_use_ignores_last_message(session_manager):
"""Test that orphaned toolUse in the last message is not fixed."""
def test_fix_broken_tool_use_repairs_orphaned_last_message(session_manager):
"""Test that orphaned toolUse in the last message is repaired with a synthetic toolResult."""
messages = [
{"role": "user", "content": [{"text": "Hello"}]},
{
Expand All @@ -430,8 +430,13 @@ def test_fix_broken_tool_use_ignores_last_message(session_manager):

fixed_messages = session_manager._fix_broken_tool_use(messages)

# Should remain unchanged since toolUse is in last message
assert fixed_messages == messages
# A synthetic toolResult should be appended for the orphaned toolUse
assert len(fixed_messages) == 3
assert fixed_messages[2]["role"] == "user"
tool_result_ids = [
c["toolResult"]["toolUseId"] for c in fixed_messages[2]["content"] if "toolResult" in c
]
assert "last-message-123" in tool_result_ids


def test_fix_broken_tool_use_does_not_change_valid_message(session_manager):
Expand Down