Understand the Machine Behind Money.

{  "id": "rrp-floor-mechanics",  "title": "The Floor Under Every Overnight Rate",  "subtitle": "Watch the ON RRP facility drain reserves and set the price of cash.",  "icon": "🪜",  "difficulty": "advanced",  "challenges": [    {      "id": "rrp-flow-step",      "type": "t_account_flow",      "prompt": "A money market fund parks $500M at the Fed's ON RRP window overnight.",      "explanation": "Total Fed liabilities are unchanged: $500M moved from the reserves line to the reverse repo line. But reserves are base money and reverse repos are not.",      "currency": "USD",      "entities": [        { "id": "fed", "label": "Federal Reserve", "tier": "central_bank",          "openingLines": [            { "account": "Commercial bank reserves", "side": "liability", "amount": 3100000000000 },            { "account": "Reverse repurchase agreements", "side": "liability", "amount": 420000000000 }          ] },        { "id": "mmf", "label": "Money Market Fund", "tier": "shadow_bank",          "role": "Cannot hold reserves" }      ],      "expectedShifts": [        { "entityId": "fed", "side": "liability",          "account": "Reverse repurchase agreements", "delta": 500000000 },        { "entityId": "fed", "side": "liability",          "account": "Commercial bank reserves", "delta": -500000000 },        { "entityId": "mmf", "side": "asset",          "account": "Reverse repo claims", "delta": 500000000 },        { "entityId": "mmf", "side": "asset",          "account": "Bank deposits", "delta": -500000000 }      ],      "aggregateEffects": [        { "aggregate": "M0", "direction": "contract",          "note": "Reserves fell by $500M. Reverse repos are a Fed liability too, but they are not base money." }      ],      "xp": 30    }  ]}