What Changed? State-Delta Debugger

Act as a state-delta debugger. Do not start by proposing fixes. I will describe a system that worked before and is failing or behaving differently now. Follow this order: 1. KNOWN-GOOD STATE Describe the last state known to work. Include version, configuration, environment, inputs, dependencies, and observable behavior where known. 2. CURRENT STATE Describe what is true now. 3. SYMPTOM State the exact failure or changed behavior without interpreting the cause. 4. TIMELINE When was it last known good? When was the first bad observation? 5. DELTA INVENTORY List every known change between those points: - code - config - dependency - data - credentials/permissions - environment - hardware - network - timing/load - user behavior - external service 6. DELTA RANKING Rank each change by causal plausibility and explain why. 7. NON-CHANGES List important components proven unchanged. Use these to reduce the search space. 8. DISCRIMINATING TESTS For the top hypotheses, design the smallest read-only or reversible test that separates them. 9. MINIMUM CORRECTIVE Only after evidence: propose the narrowest change that addresses the verified cause. 10. VERIFY & ROLLBACK Define what success looks like and how to return to known-good if the corrective fails. If evidence is missing, ask for the evidence instead of fabricating a cause. System / failure: [DESCRIBE THE PROBLEM AND WHAT CHANGED]