feat: add per_turn parameter to SlidingWindowConversationManager #4

github-actions · 2025-12-17T21:58:13Z

Problem

When agents perform many tool operations (e.g., web browsing with screenshots), message history grows rapidly and the agent loop slows down. Currently, ConversationManager.apply_management() only runs at the end of execution in the finally block, causing performance degradation during long-running agent loops.

Solution

Add per_turn parameter to SlidingWindowConversationManager that enables proactive message management during the agent loop by leveraging the hooks system.

Resolves #3

Public API Changes

SlidingWindowConversationManager

Before:

manager = SlidingWindowConversationManager(
    window_size=40,
    should_truncate_results=True
)

After:

manager = SlidingWindowConversationManager(
    window_size=40,
    should_truncate_results=True,
    per_turn=True  # or per_turn=5 for every 5 model calls
)
# Can be changed dynamically
manager.per_turn = 3

Parameter Options

per_turn=False (default): Current behavior - management only at end
per_turn=True: Apply management before every model call
per_turn=N (int): Apply management before every N model calls

HookProvider Protocol

Added @runtime_checkable to HookProvider protocol to enable proper isinstance checks.

Implementation Approach

SlidingWindowConversationManager implements HookProvider.register_hooks() and subscribes to BeforeModelCallEvent
Agent auto-registers conversation_manager as hook provider if it implements the protocol
Callback checks per_turn dynamically (not at registration) to support runtime changes
State persistence includes model_call_count for session restoration
Finally block still calls apply_management() for robustness

Impact

Benefits:

Prevents performance degradation in tool-heavy workflows
Reduces token costs for long-running agents
Enables fine-tuned control over context management frequency

Tradeoffs:

More aggressive management removes conversation history the agent uses for decision-making
Requires understanding agent's context needs to choose appropriate per_turn value

Backward Compatibility

✓ Default per_turn=False maintains current behavior
✓ No breaking changes
✓ Other conversation managers (Summarizing, Null) unaffected

Enable SlidingWindowConversationManager to apply message management during the agent loop execution by implementing per_turn functionality. Changes: - Add per_turn parameter (bool | int, default: False) to control when message management is applied - Implement register_hooks method to register AfterToolCallEvent callback - Add _on_after_tool_call callback to apply management based on per_turn - Update get_state and restore_from_session to persist _tool_call_count - Auto-register conversation_manager as hook in Agent.__init__ if it implements register_hooks method - Add comprehensive test suite with 25 test cases Resolves #3

zastrowm · 2025-12-17T22:02:29Z

src/strands/agent/conversation_manager/sliding_window_conversation_manager.py

+        Args:
+            event: The after tool call event containing the agent and tool execution details.
+        """
+        self._tool_call_count += 1


Track model calls instead of tool calls, since you could have N tools execute per "turn"

Good point! Will change to track model calls using AfterModelCallEvent instead.

zastrowm · 2025-12-17T22:03:04Z

src/strands/agent/agent.py

            self.hooks.add_hook(self._session_manager)

+        # Check if conversation_manager can provide hooks
+        if hasattr(self.conversation_manager, "register_hooks"):


No, check if it derives from HookProvider

Will update to use isinstance check with HookProvider.

zastrowm · 2025-12-17T22:06:03Z

tests/strands/agent/test_sliding_window_conversation_manager_per_turn.py

We have tests for the conversation manager (search for test_sliding_window_conversation_manager_with_tool_results_truncated) move these to be in ther

Will move tests to existing test_conversation_manager.py file.

zastrowm · 2025-12-17T22:08:54Z

src/strands/agent/conversation_manager/sliding_window_conversation_manager.py

+            Optional list of messages to prepend to the agent's messages.
+        """
+        result = super().restore_from_session(state)
+        self._tool_call_count = state.get("_tool_call_count", 0)


We don't have to use an underscore since we own the implementation

Will remove underscore prefix from model_call_count.

zastrowm · 2025-12-17T22:09:09Z

/strands

Changes based on PR review feedback: - Track model calls instead of tool calls using AfterModelCallEvent - Rename counter from _tool_call_count to model_call_count (remove underscore) - Use hasattr/callable check instead of isinstance for HookProvider protocol - Move tests from standalone file to existing test_conversation_manager.py All 40 tests passing (15 existing + 25 new).

src/strands/agent/conversation_manager/sliding_window_conversation_manager.py

zastrowm · 2025-12-18T14:38:53Z

src/strands/agent/conversation_manager/sliding_window_conversation_manager.py

+                - True: Apply management after every model call
+                - int (e.g., 3): Apply management after every N model calls
+
+                When to use per_turn: If your agent performs many tool operations in loops


Make this much more concise. Just talk about how this can reduce the context that the agent receives which can speed up agents and/or reduce costs, at the expense of removing context that the agent uses to guide the next step

Will simplify to focus on context reduction benefits vs tradeoffs.

You didn't make this more concise

src/strands/agent/conversation_manager/sliding_window_conversation_manager.py

src/strands/agent/agent.py

tests/strands/agent/test_conversation_manager.py

test_per_turn_updated.log

zastrowm · 2025-12-18T14:47:58Z

/strands

Changes: - Mark HookProvider as @runtime_checkable and use isinstance check in Agent - Change from AfterModelCallEvent to BeforeModelCallEvent for better timing - Move per_turn check to callback for dynamic changes - Rename model_call_count (removed underscore) - Simplify per_turn docstring to focus on context reduction tradeoffs - Convert test classes to concise function-style tests matching existing patterns - Elevate all imports to top of file - Remove implementation detail tests and focus on behavior - Add test for dynamic per_turn changes - Remove test_per_turn_updated.log file All 24 tests passing (15 existing + 9 new concise per_turn tests)

zastrowm · 2025-12-18T18:31:53Z

/strands

zastrowm · 2025-12-18T18:31:20Z

tests/strands/agent/test_conversation_manager.py

+        assert mock.call_count >= 1
+
+
+def test_per_turn_integer_manages_every_n_calls():


Up above, we have a bunch of tests that use data-driven test cases.

Many of these tests overlap with that - Rewrite the tests that make sense as additional test-cases

zastrowm · 2025-12-18T19:01:32Z

/strands

Changes: - Make per_turn docstring much more concise (2 sentences vs 5) - Use BeforeModelCallEvent instead of AfterModelCallEvent for better timing - Move per_turn check to callback (always register, check in callback for dynamic changes) - Mark HookProvider as @runtime_checkable and use isinstance in Agent - Convert tests to data-driven parametrized style matching existing patterns - Consolidate 9 function tests into 2 parametrized tests + 2 focused tests - Remove implementation detail tests (hook registration checks) - Elevate imports to top of file (remove local imports) - Remove test log file All 27 tests passing (15 existing + 12 new per_turn tests)

zastrowm · 2025-12-19T19:01:10Z

/strands update the PR description according to the guidelines

zastrowm requested changes Dec 17, 2025

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zastrowm mentioned this pull request Dec 18, 2025

[FEATURE] Import GitHub agents from TypeScript strands-agents/sdk-python#1363

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		assert mock.call_count >= 1


		def test_per_turn_integer_manages_every_n_calls():

feat: add per_turn parameter to SlidingWindowConversationManager #4

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Problem

Solution

Public API Changes

SlidingWindowConversationManager

Parameter Options

HookProvider Protocol

Implementation Approach

Impact

Backward Compatibility

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