Summary Significantly expanded the test coverage for ZIOApp to verify its correct behavior across various scenarios.

Expanded from 34 → 57 tests (+68% more coverage)

New test suites added: Fiber Management (3 tests) - spawning, waiting, background fibers Signal Handler Integration (2 tests) - atomic flag, multiple concurrent apps Runtime & Lifecycle (3 tests) - runtime access, fiber ID, independent invocations Error Handling & Logging (3 tests) - typed errors, error preservation Scope & Resource Management (3 tests) - scoped resources, bootstrap scopes, nested scopes Interruption & Cancellation (2 tests) - external interruption, cause preservation Exit Behavior (2 tests) - exit codes for different outcomes Composition Operator (3 tests) - parallel execution, mixed environments Timeout Behavior (2 tests) - zero timeout, finite timeout cleanup Test Results: All 57 tests pass

This provides comprehensive coverage of ZIOApp’s core behaviors as requested in the bounty.

Fixes #9909

/claim #9909