fix finance balance delta recharges

backend/app/models/snapshot.py

@@ -1,5 +1,5 @@
 from datetime import datetime, timezone
-from sqlalchemy import Index, Integer, Text, DateTime, ForeignKey, text
+from sqlalchemy import Float, Index, Integer, Text, DateTime, ForeignKey, text
 from sqlalchemy.orm import mapped_column, Mapped
 from app.database import Base
 
@@ -15,3 +15,16 @@ class UpstreamRateSnapshot(Base):
     __table_args__ = (
         Index("ix_snapshot_upstream_captured", "upstream_id", text("captured_at DESC")),
     )
+
+
+class UpstreamBalanceSnapshot(Base):
+    __tablename__ = "upstream_balance_snapshots"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, index=True)
+    upstream_id: Mapped[int] = mapped_column(Integer, ForeignKey("upstreams.id", ondelete="CASCADE"), index=True)
+    balance: Mapped[float] = mapped_column(Float, nullable=False)
+    captured_at: Mapped[datetime] = mapped_column(DateTime, default=lambda: datetime.now(timezone.utc), index=True)
+
+    __table_args__ = (
+        Index("ix_balance_snap_upstream_captured", "upstream_id", text("captured_at DESC")),
+    )

backend/app/models/upstream.py

@@ -35,6 +35,8 @@ class Upstream(Base):
     # Balance alert
     balance_alert_threshold: Mapped[Optional[float]] = mapped_column(Float, nullable=True)
     balance_alert_notified: Mapped[bool] = mapped_column(Boolean, default=False)
+    # Finance cost mode: "usage_stats" (default) or "balance_delta"
+    finance_cost_mode: Mapped[str] = mapped_column(String(32), default="usage_stats")
     created_at: Mapped[datetime] = mapped_column(DateTime, default=lambda: datetime.now(timezone.utc))
     updated_at: Mapped[datetime] = mapped_column(
         DateTime, default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc)

backend/app/models/upstream_recharge_event.py

@@ -0,0 +1,24 @@
+from datetime import date, datetime, timezone
+
+from sqlalchemy import Date, DateTime, Float, ForeignKey, Index, Integer, String, Text
+from sqlalchemy.orm import Mapped, mapped_column
+
+from app.database import Base
+
+
+class UpstreamRechargeEvent(Base):
+    __tablename__ = "upstream_recharge_events"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, index=True)
+    upstream_id: Mapped[int] = mapped_column(Integer, ForeignKey("upstreams.id", ondelete="CASCADE"), index=True)
+    recharge_date: Mapped[date] = mapped_column(Date, nullable=False)
+    amount: Mapped[float] = mapped_column(Float, nullable=False)
+    note: Mapped[str] = mapped_column(Text, default="")
+    created_at: Mapped[datetime] = mapped_column(DateTime, default=lambda: datetime.now(timezone.utc))
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime, default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc)
+    )
+
+    __table_args__ = (
+        Index("ix_recharge_upstream_date", "upstream_id", "recharge_date"),
+    )