Refactor economics to expense-record ledger with correct Bubble cost

Replace pre-aggregated costs.json with expense_records.json (48 line-item
records) and payment_records.json. All monthly and cumulative totals are
computed deterministically in observatory/ledger.py. Correct Bubble.io to
$32/mo (since Feb 2025) — infrastructure €69.44/mo not €72.20.

projects/coulomb-pricing/observatory/load.py

@@ -4,16 +4,15 @@ import json
 from decimal import Decimal
 from pathlib import Path
 
-_ZERO = Decimal("0")
-
+from .ledger import build_monthly_ledger
 from .models import (
     Budget,
-    CostEntry,
+    ExpenseRecord,
     MembershipRecord,
     MonthlyPlatformCost,
+    PaymentRecord,
     PricingModel,
     Product,
-    RevenueEntry,
 )
 
 
@@ -67,55 +66,38 @@ def load_pricing_models(data_dir: Path | None = None) -> list[PricingModel]:
     ]
 
 
-def _parse_cost_entries(items: list[dict]) -> list[CostEntry]:
+def load_fx_rates(data_dir: Path | None = None) -> dict[str, Decimal]:
+    raw = _read_json((data_dir or default_data_dir()) / "expense_records.json")
+    return {pair: _money(rate) for pair, rate in raw.get("fx_rates", {}).items()}
+
+
+def load_expense_records(data_dir: Path | None = None) -> list[ExpenseRecord]:
+    raw = _read_json((data_dir or default_data_dir()) / "expense_records.json")
     return [
-        CostEntry(
+        ExpenseRecord(
             id=item["id"],
-            name=item["name"],
-            category=item["category"],
+            period=item["period"],
+            vendor=item["vendor"],
+            description=item["description"],
+            cost_class=item["cost_class"],
             amount=_money(item["amount"]),
             currency=item["currency"],
-            cadence=item["cadence"],
-            allocation=item["allocation"],
+            source=item["source"],
         )
-        for item in items
+        for item in raw["records"]
     ]
 
 
-def load_cost_rate_card(data_dir: Path | None = None) -> tuple[list[CostEntry], dict[str, Decimal]]:
-    raw = _read_json((data_dir or default_data_dir()) / "costs.json")
-    items = raw.get("rate_card", raw.get("entries", []))
-    fx = {pair: _money(rate) for pair, rate in raw.get("fx_rates", {}).items()}
-    return _parse_cost_entries(items), fx
-
-
-def load_monthly_platform_costs(data_dir: Path | None = None) -> list[MonthlyPlatformCost]:
-    raw = _read_json((data_dir or default_data_dir()) / "costs.json")
-    rows: list[MonthlyPlatformCost] = []
-    for item in raw.get("monthly_history", []):
-        if "infrastructure_cost" in item:
-            infrastructure = _money(item["infrastructure_cost"])
-            processing = _money(item.get("payment_processing_cost", "0"))
-        else:
-            # Legacy single platform_cost field treated as infrastructure only.
-            infrastructure = _money(item["platform_cost"])
-            processing = _ZERO
-        rows.append(
-            MonthlyPlatformCost(
-                period=item["period"],
-                infrastructure_cost=infrastructure,
-                payment_processing_cost=processing,
-                active_members=item["active_members"],
-                gross_revenue=_money(item["gross_revenue"]),
-            )
-        )
-    return rows
-
-
-def load_revenue(data_dir: Path | None = None) -> list[RevenueEntry]:
-    raw = _read_json((data_dir or default_data_dir()) / "revenue.json")
+def load_payment_records(data_dir: Path | None = None) -> list[PaymentRecord]:
+    root = data_dir or default_data_dir()
+    path = root / "payment_records.json"
+    if not path.exists():
+        # Backward compatibility with legacy revenue.json
+        path = root / "revenue.json"
+    raw = _read_json(path)
+    items = raw.get("records", raw.get("entries", []))
     return [
-        RevenueEntry(
+        PaymentRecord(
             id=item["id"],
             period=item["period"],
             gross_amount=_money(item["gross_amount"]),
@@ -124,8 +106,9 @@ def load_revenue(data_dir: Path | None = None) -> list[RevenueEntry]:
             net_amount=_money(item["net_amount"]),
             currency=item["currency"],
             source=item["source"],
+            member_count=item.get("member_count", 0),
         )
-        for item in raw["entries"]
+        for item in items
     ]
 
 
@@ -143,5 +126,16 @@ def load_membership(data_dir: Path | None = None) -> list[MembershipRecord]:
     ]
 
 
+def load_monthly_ledger(data_dir: Path | None = None) -> list[MonthlyPlatformCost]:
+    root = data_dir or default_data_dir()
+    return build_monthly_ledger(
+        load_budget(root),
+        load_expense_records(root),
+        load_payment_records(root),
+        load_membership(root),
+        load_fx_rates(root),
+    )
+
+
 def latest_period(monthly_costs: list[MonthlyPlatformCost]) -> str:
     return max(item.period for item in monthly_costs)