fix(event-loop): ensure all cycle metrics include end time and duration

[stephentreacy]

Description

Event loop cycle metrics (end_time and duration) were not being recorded for cycles that ended with a recursive call. This caused total_duration and average_cycle_time in the response metrics to be inaccurate, making it difficult to monitor agent performance in multi-cycle invocations.

Response metric traces would like like this, where total_duration is only including the Cycle 2 duration:

{
  "total_cycles": 2,
  "total_duration": 2.97,
  "traces": [
    {
      "name": "Cycle 1",
      "start_time": 1772822921.485906,
      "end_time": null,
      "duration": null,
      "children": [
        {
          "name": "stream_messages",
          "start_time": 1772822921.486195,
          "end_time": 1772822924.446701,
          "duration": 2.96
        },
        {
          "name": "Tool: tool_name",
          "start_time": 1772822924.447283,
          "end_time": 1772822931.842052,
          "duration": 7.39
        },
        {
          "name": "Recursive call",
          "start_time": 1772822931.842254,
          "end_time": 1772822934.810739,
          "duration": 2.97
        }
      ]
    },
    {
      "name": "Cycle 2",
      "start_time": 1772822931.842278,
      "end_time": 1772822934.810579,
      "duration": 2.97,
      "children": [
        {
          "name": "stream_messages",
          "start_time": 1772822931.842385,
          "end_time": 1772822934.810402,
          "duration": 2.97
        }
      ]
    }
  ]
}

Related Issues

Documentation PR

Type of Change

Bug fix

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• I ran hatch run prepare

Tested locally with recursive call scenarios, verified cycle metrics now include accurate end_time and duration values

Cycle 1 duration includes all child durations except the recursive call.

{
  "total_cycles": 2,
  "total_duration": 14.80,
  "traces": [
    {
      "name": "Cycle 1",
      "start_time": 1772825264.482746,
      "end_time": 1772825275.644092,
      "duration": 11.16,
      "children": [
        {
          "name": "stream_messages",
          "start_time": 1772825264.483011,
          "end_time": 1772825267.999054,
          "duration": 3.52
        },
        {
          "name": "Tool: tool_name",
          "start_time": 1772825268.000930,
          "end_time": 1772825275.643905,
          "duration": 7.64
        },
        {
          "name": "Recursive call",
          "start_time": 1772825275.644141,
          "end_time": 1772825279.281506,
          "duration": 3.64
        }
      ]
    },
    {
      "name": "Cycle 2",
      "start_time": 1772825275.644161,
      "end_time": 1772825279.281480,
      "duration": 3.64,
      "children": [
        {
          "name": "stream_messages",
          "start_time": 1772825275.644274,
          "end_time": 1772825279.281442,
          "duration": 3.64
        }
      ]
    }
  ]
}

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[Copilot]

Pull request overview

Fixes inaccurate event-loop cycle timing metrics when a cycle ends by recursing into another event_loop_cycle (e.g., after tool execution), ensuring cycle traces get end_time/duration recorded so aggregate response metrics (like total/average duration) are correct for multi-cycle invocations.

Changes:

• End tool-execution cycles’ metrics before deciding to stop or recurse, ensuring recursive paths still record end_time and duration.
• Add a regression test covering the recursive-call scenario and asserting end_cycle is invoked for both the tool cycle and the subsequent text cycle.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/strands/event_loop/event_loop.py	Moves end_cycle so tool cycles are always finalized before recursion/stop logic.
tests/strands/event_loop/test_event_loop.py	Adds an async test to verify cycle-metrics finalization occurs in recursive tool-use flows.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Unshure]

Hi @stephentreacy , thanks for raising this. After you address the failing workflows, I am happy to approve and merge this change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[github-actions]

Assessment: Approve

Clean fix that correctly addresses the cycle metrics regression by moving end_cycle before the stop-vs-recurse conditional, ensuring all cycles record end_time and duration.

Review Notes

• Fix correctness: Moving the end_cycle call above the conditional ensures metrics are recorded for cycles that recurse, not just cycles that stop.
• Test coverage: New test validates the call count, though using wraps= would also verify actual trace values.
• Pre-existing: The attributes inconsistency across other end_cycle call sites is out of scope for this bug fix.

Good fix with clear before/after examples in the PR description.