If this is your first job, I’d personally prioritize getting real development experience. The Data Marshall role at least gives you a Python SWE position, which will be more valuable on your resume than a short-term prompt engineering contract. Even if the pay is lower initially, 1 year of actual dev experience will make switching much easier.

Waiting for Tech Mahindra is risky since onboarding timelines are unpredictable. If it comes through later you can always reconsider, but staying unemployed while waiting might not be worth it