fix: repair orphaned toolUser in last message during session restore

src/strands/session/repository_session_manager.py

@@ -245,17 +245,16 @@ def initialize(self, agent: "Agent", **kwargs: Any) -> None:
     def _fix_broken_tool_use(self, messages: list[Message]) -> list[Message]:
         """Fix broken tool use/result pairs in message history.
 
-        This method handles two issues:
+        This method handles three issues:
         1. Orphaned toolUse messages without corresponding toolResult.
            Before 1.15.0, strands had a bug where they persisted sessions with a potentially broken messages array.
            This method retroactively fixes that issue by adding a tool_result outside of session management.
            After 1.15.0, this bug is no longer present.
-        2. Orphaned toolResult messages without corresponding toolUse (e.g., when pagination truncates messages)
+        2. Orphaned toolUse as the last message (e.g., process terminated during tool execution).
+        3. Orphaned toolResult messages without corresponding toolUse (e.g., when pagination truncates messages)
 
         Args:
             messages: The list of messages to fix
-            agent_id: The agent ID for fetching previous messages
-            removed_message_count: Number of messages removed by the conversation manager
 
         Returns:
             Fixed list of messages with proper tool use/result pairs
@@ -273,37 +272,38 @@ 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 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):
-                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})
+                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 missing_tool_use_ids:
+                    logger.warning(
+                        "Session message history has an orphaned toolUse with no toolResult. "
+                        "Adding toolResult content blocks to create valid conversation."
+                    )
+                    missing_content_blocks = generate_missing_tool_result_content(missing_tool_use_ids)
+
+                    if tool_result_ids:
+                        messages[index + 1]["content"].extend(missing_content_blocks)
+                    else:
+                        messages.insert(index + 1, {"role": "user", "content": missing_content_blocks})
+            else:
+                # Last message is an orphaned toolUse — typically caused by process termination during tool execution
+                logger.warning(
+                    "Session message history ends with an orphaned toolUse. "
+                    "Adding toolResult to create valid conversation."
+                )
+                messages.append({"role": "user", "content": generate_missing_tool_result_content(tool_use_ids)})
+
         return messages
 
     def sync_multi_agent(self, source: "MultiAgentBase", **kwargs: Any) -> None:

tests/strands/session/test_repository_session_manager.py

@@ -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_fixes_last_message(session_manager):
+    """Test that orphaned toolUse in the last message is fixed by appending a toolResult."""
     messages = [
         {"role": "user", "content": [{"text": "Hello"}]},
         {
@@ -430,8 +430,12 @@ 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
+    assert len(fixed_messages) == 3
+    appended = fixed_messages[2]
+    assert appended["role"] == "user"
+    assert len(appended["content"]) == 1
+    assert appended["content"][0]["toolResult"]["toolUseId"] == "last-message-123"
+    assert appended["content"][0]["toolResult"]["status"] == "error"
 
 
 def test_fix_broken_tool_use_does_not_change_valid_message(session_manager):