refactor(hooks): fire Before/AfterReduceContextEvent inside reduce_context() implementations

Hooks were previously fired only from agent.py around the overflow-path
call to reduce_context(). SlidingWindowConversationManager.apply_management()
also calls reduce_context() for per-turn trimming, so hooks never fired
on that path.

Move hook invocations into reduce_context() in both
SlidingWindowConversationManager and SummarizerConversationManager, using
the synchronous invoke_callbacks(). Remove the now-redundant async calls
from agent.py. Update tests accordingly.

Author: Zelys-DFKH

src/strands/agent/conversation_manager/sliding_window_conversation_manager.py

@@ -6,7 +6,7 @@
 if TYPE_CHECKING:
     from ...agent.agent import Agent
 
-from ...hooks import BeforeModelCallEvent, BeforeReduceContextEvent, AfterReduceContextEvent, HookRegistry
+from ...hooks import AfterReduceContextEvent, BeforeModelCallEvent, BeforeReduceContextEvent, HookRegistry
 from ...types.content import ContentBlock, Messages
 from ...types.exceptions import ContextWindowOverflowException
 from ...types.tools import ToolResultContent
@@ -171,7 +171,6 @@ def reduce_context(self, agent: "Agent", e: Exception | None = None, **kwargs: A
                 Such as when the conversation is already minimal or when tool result messages cannot be properly
                 converted.
         """
-        # Fire before event
         agent.hooks.invoke_callbacks(BeforeReduceContextEvent(agent=agent, exception=e))
 
         messages = agent.messages
@@ -185,6 +184,7 @@ def reduce_context(self, agent: "Agent", e: Exception | None = None, **kwargs: A
             results_truncated = self._truncate_tool_results(messages, oldest_message_idx_with_tool_results)
             if results_truncated:
                 logger.debug("message_index=<%s> | tool results truncated", oldest_message_idx_with_tool_results)
+                agent.hooks.invoke_callbacks(AfterReduceContextEvent(agent=agent))
                 return
 
         # Try to trim index id when tool result cannot be truncated anymore
@@ -216,7 +216,6 @@ def reduce_context(self, agent: "Agent", e: Exception | None = None, **kwargs: A
         # Overwrite message history
         messages[:] = messages[trim_index:]
 
-        # Fire after event
         agent.hooks.invoke_callbacks(AfterReduceContextEvent(agent=agent))
 
     def _truncate_tool_results(self, messages: Messages, msg_idx: int) -> bool:

src/strands/agent/conversation_manager/summarizing_conversation_manager.py

@@ -7,13 +7,13 @@
 
 from ..._async import run_async
 from ...event_loop.streaming import process_stream
+from ...hooks import AfterReduceContextEvent, BeforeReduceContextEvent
 from ...tools._tool_helpers import noop_tool
 from ...tools.registry import ToolRegistry
 from ...types.content import Message
 from ...types.exceptions import ContextWindowOverflowException
 from ...types.tools import AgentTool
 from .conversation_manager import ConversationManager
-from ...hooks import BeforeReduceContextEvent, AfterReduceContextEvent
 
 if TYPE_CHECKING:
     from ..agent import Agent
@@ -136,7 +136,6 @@ def reduce_context(self, agent: "Agent", e: Exception | None = None, **kwargs: A
         Raises:
             ContextWindowOverflowException: If the context cannot be summarized.
         """
-        # Fire before event
         agent.hooks.invoke_callbacks(BeforeReduceContextEvent(agent=agent, exception=e))
 
         try:
@@ -175,7 +174,6 @@ def reduce_context(self, agent: "Agent", e: Exception | None = None, **kwargs: A
             # Replace the summarized messages with the summary
             agent.messages[:] = [self._summary_message] + remaining_messages
 
-            # Fire after event
             agent.hooks.invoke_callbacks(AfterReduceContextEvent(agent=agent))
 
         except Exception as summarization_error:

tests/strands/agent/test_agent.py

@@ -2781,13 +2781,18 @@ async def test_stream_async_fires_before_and_after_reduce_context_hook_events(mo
         ),
     ]
 
+    # Seed messages so SlidingWindowConversationManager.reduce_context() can trim them.
+    agent.messages[:] = [
+        {"role": "user", "content": [{"text": "msg1"}]},
+        {"role": "assistant", "content": [{"text": "resp1"}]},
+        {"role": "user", "content": [{"text": "msg2"}]},
+    ]
+
     before_events = []
     after_events = []
     agent.add_hook(lambda e: before_events.append(e), BeforeReduceContextEvent)
     agent.add_hook(lambda e: after_events.append(e), AfterReduceContextEvent)
 
-    agent.conversation_manager.reduce_context = unittest.mock.Mock()
-
     await alist(agent.stream_async("hello"))
 
     assert len(before_events) == 1

tests/strands/agent/test_summarizing_conversation_manager.py

@@ -4,6 +4,7 @@
 import pytest
 
 from strands.agent.agent import Agent
+from strands.hooks.registry import HookRegistry
 from strands.agent.conversation_manager.summarizing_conversation_manager import (
     DEFAULT_SUMMARIZATION_PROMPT,
     SummarizingConversationManager,
@@ -45,6 +46,7 @@ def __init__(self, summary_response="This is a summary of the conversation."):
         self.summary_response = summary_response
         self.system_prompt = None
         self.messages = []
+        self.hooks = HookRegistry()
         self.model = Mock()
         self.model.stream = Mock(side_effect=lambda *a, **kw: _mock_model_stream(self.summary_response))
         self.call_tracker = Mock()