[WIP] Fix duration limit problem causing soft lock state

[Copilot]

• Inspect repository structure and locate solver code/tests related to duration_limit
• Run baseline tests to identify current environment/test status
• Set up missing local test dependency and run baseline tests successfully
• Reproduce the duration_limit behavior with focused test coverage
• Implement the minimal fix in solver input handling to prevent problematic duration_limit states
• Add/adjust targeted tests for the fixed behavior
• Run targeted tests for changed areas, then run full test suite
• Run CodeQL security check and address any findings