[FEATURE] Expose ConversationManager's reduce_context() as Hook Event

[VincentBai-dotcom]

Problem Statement

I'm building observability plugin to Strands agent. The end goal is to have a dashboard listing what has the agent done during an invocation. So far I'm able to expose the tool calls, model outputs, and more, but I can't natively collect the event when the ConversationManager decides to reduce context.

Proposed Solution

Expose BeforeReduceContext and AfterReduceContext as Hook Event that allows developers to pass in custom callbacks that get executed during these two events, along with the existing Hook Event described here: https://strandsagents.com/docs/user-guide/concepts/agents/hooks/.

This can possibly solve another existing feature request too: #1679

Use Case

Need this feature such that developers can detect conversation context compaction event and collect it in their observability layer.

Alternatives Solutions

No response

Additional Context

No response

[Zelys-DFKH]

Traced the gap. The overflow handler in _execute_event_loop_cycle calls reduce_context() with no surrounding hook events. The fix adds BeforeReduceContextEvent (carries the ContextWindowOverflowException) and AfterReduceContextEvent around that call, exported from strands.hooks alongside the existing events. Opening a PR now.