What I did

Added unit tests for the upOptions.OnExit() method in cmd/compose/up_test.go.

The new test (TestUpOptions_OnExit) covers all cascade behavior modes:

• CascadeIgnore (default behavior)
• CascadeStop (--abort-on-container-exit)
• CascadeFail (--abort-on-container-failure)
• Edge case: both flags set (stop takes precedence)

This test follows the existing test patterns in the codebase, using table-driven tests with the args field containing the full upOptions struct.

Related issue

N/A

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