Complete Economic Observatory MVP (ADAPTIVE-WP-0002)

Add file-based Bubble, Stripe, and OpenRouter importers; usage attribution,
cost allocation, pricing simulator, credit wallets, and recommendations in the
dashboard API. Document whynot-design UI workflow and archive the finished
workplan with all ten tasks marked done.

projects/coulomb-pricing/observatory/usage.py

@@ -0,0 +1,48 @@
+from __future__ import annotations
+
+from decimal import Decimal, ROUND_HALF_UP
+from typing import Any
+
+TWOPLACES = Decimal("0.01")
+
+
+def _money(value: Decimal) -> Decimal:
+    return value.quantize(TWOPLACES, rounding=ROUND_HALF_UP)
+
+
+def load_usage_records(data_dir) -> list[dict[str, Any]]:
+    from pathlib import Path
+
+    from .load import _read_json, default_data_dir
+
+    root = data_dir or default_data_dir()
+    path = Path(root) / "usage_records.json"
+    if not path.exists():
+        return []
+    raw = _read_json(path)
+    return list(raw.get("records", []))
+
+
+def build_usage_summary(records: list[dict[str, Any]], period: str) -> dict:
+    period_rows = [row for row in records if row.get("period") == period]
+    by_member: dict[str, Decimal] = {}
+    by_model: dict[str, Decimal] = {}
+    total = Decimal("0")
+
+    for row in period_rows:
+        cost = Decimal(str(row.get("cost_eur", "0")))
+        total += cost
+        member_id = row.get("member_id") or "unknown"
+        model = row.get("model") or "unknown"
+        by_member[member_id] = by_member.get(member_id, Decimal("0")) + cost
+        by_model[model] = by_model.get(model, Decimal("0")) + cost
+
+    active_members = len(by_member) or 1
+    return {
+        "period": period,
+        "total_ai_spend_eur": _money(total),
+        "cost_per_active_user_eur": _money(total / active_members),
+        "by_member": {key: _money(value) for key, value in sorted(by_member.items())},
+        "by_model": {key: _money(value) for key, value in sorted(by_model.items())},
+        "record_count": len(period_rows),
+    }