Migrate all 29 money columns from float to NUMERIC/Decimal (BE-02)

Models use Money = Annotated[Decimal, PlainSerializer(float)] so storage
is exact NUMERIC(15,2) (rates 15,6) while JSON keeps emitting plain
numbers — the frontend contract is unchanged, pinned by
test_models_serialization.py. Service layers coerce to float at their
boundaries (projection math, rate multipliers, agent tool output, the
savings constants become Decimal) so no naive Decimal/float mixing can
raise. Migration 7f567c8bafdb applied to dev: per-row values and the
table sum byte-identical before/after; endpoints verified live on the
new schema. 59/59 tests green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/app/models/models.py

@@ -1,7 +1,9 @@
 import enum
 from datetime import date, datetime
-from typing import Optional
+from decimal import Decimal
+from typing import Annotated, Optional
 
+from pydantic import PlainSerializer
 from sqlalchemy import JSON, Column, UniqueConstraint
 from sqlalchemy.dialects.postgresql import JSONB
 from sqlmodel import Field, Relationship, SQLModel
@@ -12,6 +14,13 @@ from app.timeutil import utcnow
 # SQLite (tests).
 JSON_OR_JSONB = JSON().with_variant(JSONB(), "postgresql")
 
+# Monetary values: exact NUMERIC storage, but serialized to JSON as plain
+# numbers so the API contract (frontend expects `number`) is unchanged.
+# Pinned by tests/test_models_serialization.py.
+Money = Annotated[
+    Decimal, PlainSerializer(float, return_type=float, when_used="json")
+]
+
 
 class RecurringItemType(str, enum.Enum):
     INCOME = "INCOME"
@@ -106,9 +115,9 @@ class AccountBase(SQLModel):
     bank: Bank
     currency: Currency
     label: str
-    balance: float = 0.0
+    balance: Money = Field(default=Decimal("0"), max_digits=15, decimal_places=2)
     account_type: AccountType = AccountType.BANK
-    next_payment: Optional[float] = None
+    next_payment: Optional[Money] = Field(default=None, max_digits=15, decimal_places=2)
 
 
 class Account(AccountBase, table=True):
@@ -126,16 +135,16 @@ class AccountRead(AccountBase):
 
 
 class AccountUpdate(SQLModel):
-    balance: Optional[float] = None
+    balance: Optional[Money] = None
     label: Optional[str] = None
-    next_payment: Optional[float] = None
+    next_payment: Optional[Money] = None
 
 
 # --- Transaction ---
 
 
 class TransactionBase(SQLModel):
-    amount: float
+    amount: Money = Field(max_digits=15, decimal_places=2)
     currency: Currency = Currency.CRC
     merchant: str
     city: Optional[str] = None
@@ -171,7 +180,7 @@ class TransactionRead(TransactionBase):
 
 
 class TransactionUpdate(SQLModel):
-    amount: Optional[float] = None
+    amount: Optional[Money] = None
     currency: Optional[Currency] = None
     merchant: Optional[str] = None
     city: Optional[str] = None
@@ -189,14 +198,14 @@ class TransactionUpdate(SQLModel):
 class ExchangeRate(SQLModel, table=True):
     id: Optional[int] = Field(default=None, primary_key=True)
     date: datetime
-    buy_rate: float
-    sell_rate: float
+    buy_rate: Decimal = Field(max_digits=15, decimal_places=6)
+    sell_rate: Decimal = Field(max_digits=15, decimal_places=6)
     fetched_at: datetime = Field(default_factory=utcnow)
 
 
 class ExchangeRateRead(SQLModel):
-    buy_rate: float
-    sell_rate: float
+    buy_rate: Money
+    sell_rate: Money
     date: datetime
     fetched_at: datetime
 
@@ -254,7 +263,7 @@ class UserSettingsUpdate(SQLModel):
 
 class RecurringItemBase(SQLModel):
     name: str
-    amount: float
+    amount: Money = Field(max_digits=15, decimal_places=2)
     currency: Currency = Currency.CRC
     item_type: RecurringItemType
     frequency: RecurringFrequency = RecurringFrequency.MONTHLY
@@ -287,7 +296,7 @@ class RecurringItemRead(RecurringItemBase):
 
 class RecurringItemUpdate(SQLModel):
     name: Optional[str] = None
-    amount: Optional[float] = None
+    amount: Optional[Money] = None
     currency: Optional[Currency] = None
     item_type: Optional[RecurringItemType] = None
     frequency: Optional[RecurringFrequency] = None
@@ -323,15 +332,15 @@ class PensionSnapshotBase(SQLModel):
     contract_number: str
     period_start: date
     period_end: date
-    saldo_anterior: float
-    aportes: float
-    rendimientos: float
-    retiros: float
-    traslados: float
-    comision: float
-    correccion: float
-    bonificacion: float
-    saldo_final: float
+    saldo_anterior: Money = Field(max_digits=15, decimal_places=2)
+    aportes: Money = Field(max_digits=15, decimal_places=2)
+    rendimientos: Money = Field(max_digits=15, decimal_places=2)
+    retiros: Money = Field(max_digits=15, decimal_places=2)
+    traslados: Money = Field(max_digits=15, decimal_places=2)
+    comision: Money = Field(max_digits=15, decimal_places=2)
+    correccion: Money = Field(max_digits=15, decimal_places=2)
+    bonificacion: Money = Field(max_digits=15, decimal_places=2)
+    saldo_final: Money = Field(max_digits=15, decimal_places=2)
     source_filename: str
 
 
@@ -356,20 +365,20 @@ class BalanceOverride(SQLModel, table=True):
     id: Optional[int] = Field(default=None, primary_key=True)
     year: int
     month: int
-    override_balance: float
+    override_balance: Money = Field(max_digits=15, decimal_places=2)
     created_at: datetime = Field(default_factory=utcnow)
     updated_at: datetime = Field(default_factory=utcnow)
 
 
 class BalanceOverrideCreate(SQLModel):
-    override_balance: float
+    override_balance: Money
 
 
 class BalanceOverrideRead(SQLModel):
     id: int
     year: int
     month: int
-    override_balance: float
+    override_balance: Money
     updated_at: datetime
 
 
@@ -379,8 +388,8 @@ class BalanceOverrideRead(SQLModel):
 class SavingsAccrualBase(SQLModel):
     year: int
     month: int
-    memp_amount: float = 200000.0
-    mpat_amount: float = 200000.0
+    memp_amount: Money = Field(default=Decimal("200000"), max_digits=15, decimal_places=2)
+    mpat_amount: Money = Field(default=Decimal("200000"), max_digits=15, decimal_places=2)
     trigger_transaction_id: Optional[int] = None
     notes: Optional[str] = None
 
@@ -401,8 +410,8 @@ class SavingsAccrualRead(SavingsAccrualBase):
 
 
 class SavingsAccrualUpdate(SQLModel):
-    memp_amount: Optional[float] = None
-    mpat_amount: Optional[float] = None
+    memp_amount: Optional[Money] = None
+    mpat_amount: Optional[Money] = None
     notes: Optional[str] = None
 
 
@@ -418,10 +427,10 @@ class MunicipalReceiptBase(SQLModel):
     holder_name: str
     holder_cedula: str
     holder_address: str
-    subtotal: float
-    interests: float
-    iva: float
-    total: float
+    subtotal: Money = Field(max_digits=15, decimal_places=2)
+    interests: Money = Field(max_digits=15, decimal_places=2)
+    iva: Money = Field(max_digits=15, decimal_places=2)
+    total: Money = Field(max_digits=15, decimal_places=2)
     raw_charges: list[dict] = Field(
         default_factory=list,
         sa_column=Column(JSON, nullable=False, server_default="[]"),
@@ -453,13 +462,13 @@ class MunicipalReceiptRead(MunicipalReceiptBase):
 class WaterMeterReadingBase(SQLModel):
     meter_id: str
     period: str  # "YYYY-MM"
-    reading_previous: float = 0
-    reading_current: float = 0
-    consumption_m3: float
-    agua_potable: float = 0
-    serv_ambientales: float = 0
-    alcant_sanitario: float = 0
-    iva: float = 0
+    reading_previous: Money = Field(default=Decimal("0"), max_digits=15, decimal_places=2)
+    reading_current: Money = Field(default=Decimal("0"), max_digits=15, decimal_places=2)
+    consumption_m3: Money = Field(max_digits=15, decimal_places=2)
+    agua_potable: Money = Field(default=Decimal("0"), max_digits=15, decimal_places=2)
+    serv_ambientales: Money = Field(default=Decimal("0"), max_digits=15, decimal_places=2)
+    alcant_sanitario: Money = Field(default=Decimal("0"), max_digits=15, decimal_places=2)
+    iva: Money = Field(default=Decimal("0"), max_digits=15, decimal_places=2)
     is_historical: bool = False
     receipt_id: Optional[int] = Field(default=None, foreign_key="municipalreceipt.id")