🦠 Quarantine

How it works. A mystery illness swept a 12-person social network. One person — patient zero — was infected on day 0, and the illness jumped to a close contact exactly one day later, hop by hop. Everyone felt sick exactly 2 days after they were infected. Interview them all, then name patient zero.
Lab tests: you have 4. A test reveals someone's exact infection day — interviews can be off by a day (people misremember), but the lab never lies.
Scoring: 1000 − 100 per test used − 200 per wrong accusation (minimum 100 for a solved case). Solve it clean for a perfect 1000.