[tobiasraabe]

Summary

• catch BaseException at the user-task execution boundary
• retain the dedicated KeyboardInterrupt branch and existing pytask control-flow handling
• turn raw SystemExit, including SystemExit(0), into an ordinary failed task report
• verify unrelated execution, descendant skipping, and unconfiguration

Root cause

The task protocol caught Exception, but SystemExit inherits directly from BaseException. A task calling sys.exit(0) therefore escaped report creation and cleanup and could terminate pytask with a successful process status.

Impact

Raw SystemExit from task code now follows normal task failure semantics. Its exit code remains available on the reported exception, unrelated tasks continue, descendants skip, and the build returns pytask's failed-build exit code.

Validation

• uv run --group test pytest --snapshot-warn-unused: 935 passed, 39 skipped, 4 xfailed
• uv run --group test pytest tests/test_execute.py -q: 57 passed, 1 xfailed
• uv run --group typing --group test --isolated ty check --python-platform linux: passed
• project-locked uv run ruff check .: passed
• project-locked ruff format --check for changed files: passed
• all non-Ruff pre-commit hooks: passed

The repository's just recipes cannot locate their configured shell on this Windows checkout. The pre-commit Ruff 0.16 hook also reports new baseline rules across untouched main, while the project lock provides Ruff 0.15.16. This PR was checked with the project-locked Ruff version and does not alter lint configuration.