[olmaks]

__register_plugins in task-sdk/src/airflow/sdk/plugins_manager.py uses return where it means
continue:

if plugin_instance.name in loaded_plugins:
    return

The first duplicate plugin name therefore abandons the rest of the batch, and every plugin after it is
dropped — silently, since nothing is logged and _get_plugins() still returns an empty import_errors.

airflow-core carries a copy of this function and fixed it in #60498, then hardened it in #66649 (record
the duplicate in import_errors). Neither fix reached the Task SDK copy. This PR applies both, so the
block becomes byte-identical to the core one.

It matters because the Task SDK copy is the one the task-running process uses. While the two disagree,
plugins load for the scheduler and API server but go missing inside tasks — most sharply, a plugin
registering on_task_instance_running / on_task_instance_failed after a duplicate name never fires,
with no error anywhere to attribute it to. Duplicate names are not exotic: the same plugin shipped both
flattened and as a package, or present in the plugins folder and as an entry point, is enough.

Covered by a new task-sdk/tests/task_sdk/test_plugins_manager.py carrying the two cases the core suite
already has for this branch; both fail on main and pass with the change.

---

Was generative AI tooling used to co-author this PR?

• Yes

Generated-by: Claude Code following the guidelines

---

• Read the Pull Request Guidelines for more information. Note: commit author/co-author name and email in commits become permanently public when merged.
• For fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
• When adding dependency, check compliance with the ASF 3rd Party License Policy.
• For significant user-facing changes create newsfragment: {pr_number}.significant.rst, in airflow-core/newsfragments. You can add this file in a follow-up commit after the PR is created so you know the PR number.

[boring-cyborg]

Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contributors' Guide
Here are some useful points:

• Pay attention to the quality of your code (ruff, mypy and type annotations). Our prek-hooks will help you with that.
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• Please follow ASF Code of Conduct for all communication including (but not limited to) comments on Pull Requests, Mailing list and Slack.
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  In case of doubts contact the developers at:
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[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.