[Bug] Prevent empty non-interactive tasks from reading stdin

[nightcityblade]

Thank you for contributing to Swarms!

• Description: Prevent non-interactive agents from reading stdin when run() receives None, an empty string, or whitespace. Such calls now raise a clear ValueError; interactive agents retain their prompt behavior. Adds focused regression coverage that fails if stdin is accessed.
• Issue: Fixes [Bug][Agent] agent.run() with an empty task blocks on stdin even when interactive=False — a commented-out guard inverted the feature #1852
• Dependencies: None
• Tag maintainer: @kyegomez
• Twitter handle: N/A

Please make sure your PR is passing linting and testing before submitting. Run make format, make lint and make test to check this locally.

See contribution guidelines for more information on how to write/run tests, lint, etc:
https://github.com/kyegomez/swarms/blob/master/CONTRIBUTING.md

If you're adding a new integration, please include:

1. a test for the integration, preferably unit tests that do not rely on network access,
2. an example notebook showing its use.

Maintainer responsibilities:

• General / Misc / if you don't know who to tag: kye@swarms.world
• DataLoaders / VectorStores / Retrievers: kye@swarms.world
• swarms.models: kye@swarms.world
• swarms.memory: kye@swarms.world
• swarms.structures: kye@swarms.world

If no one reviews your PR within a few days, feel free to email Kye at kye@swarms.world

See contribution guidelines for more information on how to write/run tests, lint, etc: https://github.com/kyegomez/swarms

Validation performed:

• .venv/bin/python -m pytest tests/structs/test_agent.py::TestBasicAgent::test_noninteractive_empty_task_does_not_read_stdin -q — 3 passed
• .venv/bin/black . --check --diff — 955 files unchanged
• .venv/bin/ruff check . — passed

[github-actions]

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