feat: auto-capitalize the first letter of transaction descriptions

Transactions/recurring templates entered with mixed casing ("траты на
продукты") are now capitalized on create/update via a Pydantic validator,
so the fix applies to every client, not just the web UI. Adds a one-off
backfill script for existing rows.

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

backend/app/core/text.py

@@ -0,0 +1,12 @@
+"""Shared text-formatting helpers."""
+
+
+def capitalize_first_letter(value: str) -> str:
+    """Uppercase the first character, leaving the rest of the string untouched.
+
+    Unlike str.capitalize()/str.title(), this never lowercases the rest of the
+    string — "iPhone 15" stays "iPhone 15", not "Iphone 15".
+    """
+    if not value:
+        return value
+    return value[0].upper() + value[1:]

backend/app/schemas/recurring.py

@@ -1,8 +1,9 @@
 from datetime import date as date_
 from decimal import Decimal
 
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, field_validator
 
+from app.core.text import capitalize_first_letter
 from app.models.enums import RecurringFrequency, TransactionType
 
 
@@ -18,6 +19,13 @@ class RecurringTransactionCreate(BaseModel):
     frequency: RecurringFrequency
     anchor_date: date_
 
+    # Keeps templates consistent with regular transactions — see
+    # app/schemas/transaction.py for the same rule.
+    @field_validator("description")
+    @classmethod
+    def _capitalize_description(cls, value: str) -> str:
+        return capitalize_first_letter(value)
+
 
 class RecurringTransactionUpdate(BaseModel):
     account_id: int | None = None
@@ -32,6 +40,11 @@ class RecurringTransactionUpdate(BaseModel):
     anchor_date: date_ | None = None
     is_active: bool | None = None
 
+    @field_validator("description")
+    @classmethod
+    def _capitalize_description(cls, value: str | None) -> str | None:
+        return capitalize_first_letter(value) if value is not None else None
+
 
 class RecurringTransactionRead(BaseModel):
     id: int

backend/app/schemas/transaction.py

@@ -1,8 +1,9 @@
 from datetime import date as date_
 from decimal import Decimal
 
-from pydantic import BaseModel, ConfigDict, Field, model_validator
+from pydantic import BaseModel, ConfigDict, Field, field_validator, model_validator
 
+from app.core.text import capitalize_first_letter
 from app.models.enums import TransactionType
 from app.schemas.account import AccountRead
 from app.schemas.category import CategoryRead
@@ -19,6 +20,13 @@ class TransactionBase(BaseModel):
     notes: str | None = None
     date: date_
 
+    # Auto-capitalizes "траты на продукты" -> "Траты на продукты" so mixed
+    # casing from quick manual entry doesn't need fixing by hand later.
+    @field_validator("description")
+    @classmethod
+    def _capitalize_description(cls, value: str) -> str:
+        return capitalize_first_letter(value)
+
     @model_validator(mode="after")
     def _validate_type_specific_fields(self) -> "TransactionBase":
         if self.type == TransactionType.TRANSFER and not self.transfer_account_id:
@@ -47,6 +55,11 @@ class TransactionUpdate(BaseModel):
     notes: str | None = None
     date: date_ | None = None
 
+    @field_validator("description")
+    @classmethod
+    def _capitalize_description(cls, value: str | None) -> str | None:
+        return capitalize_first_letter(value) if value is not None else None
+
 
 class TransactionRead(TransactionBase):
     model_config = ConfigDict(from_attributes=True)

backend/scripts/capitalize_transaction_descriptions.py

@@ -0,0 +1,43 @@
+"""One-off backfill: capitalizes the first letter of every existing
+transaction/recurring-template description, so historical rows entered with
+mixed casing ("покупка продуктов", "ПОКУПКА хлеба") match the auto-
+capitalization now applied on create/update (see app/core/text.py and the
+description validators in app/schemas/transaction.py, app/schemas/recurring.py).
+
+Run it once against a running stack with:
+
+    docker compose exec backend python -m scripts.capitalize_transaction_descriptions
+
+Safe to re-run — already-capitalized descriptions are left untouched.
+"""
+import asyncio
+
+from sqlalchemy import select
+
+from app.core.text import capitalize_first_letter
+from app.db.session import AsyncSessionLocal
+from app.models import RecurringTransaction, Transaction
+
+
+async def _capitalize_all(session, model) -> int:
+    result = await session.execute(select(model))
+    updated = 0
+    for row in result.scalars().all():
+        fixed = capitalize_first_letter(row.description)
+        if fixed != row.description:
+            row.description = fixed
+            updated += 1
+    return updated
+
+
+async def main() -> None:
+    async with AsyncSessionLocal() as session:
+        transactions_updated = await _capitalize_all(session, Transaction)
+        recurring_updated = await _capitalize_all(session, RecurringTransaction)
+        await session.commit()
+        print(f"Transactions updated: {transactions_updated}")
+        print(f"Recurring templates updated: {recurring_updated}")
+
+
+if __name__ == "__main__":
+    asyncio.run(main())

backend/tests/test_transactions.py

@@ -24,6 +24,26 @@ async def test_create_expense_rejects_income_category(client: AsyncClient, accou
     assert resp.status_code == 400
 
 
+async def test_create_capitalizes_description_first_letter(client: AsyncClient, account_id, categories):
+    category = categories["Groceries"]
+    resp = await client.post(
+        "/transactions",
+        json=_txn(account_id, category_id=category["id"], description="траты на продукты"),
+    )
+    assert resp.status_code == 201
+    assert resp.json()["description"] == "Траты на продукты"
+
+
+async def test_update_capitalizes_description_first_letter(client: AsyncClient, account_id, categories):
+    category = categories["Groceries"]
+    created = await client.post("/transactions", json=_txn(account_id, category_id=category["id"]))
+    txn_id = created.json()["id"]
+
+    resp = await client.patch(f"/transactions/{txn_id}", json={"description": "new coffee shop"})
+    assert resp.status_code == 200
+    assert resp.json()["description"] == "New coffee shop"
+
+
 async def test_create_income_rejects_expense_category(client: AsyncClient, account_id, categories):
     expense_category = categories["Groceries"]
     resp = await client.post(
@@ -97,7 +117,7 @@ async def test_list_filters_by_year_and_month_excludes_other_months(client: Asyn
     resp = await client.get("/transactions", params={"year": 2021, "month": 8})
     body = resp.json()
     assert body["total"] == 1
-    assert [item["description"] for item in body["items"]] == ["august transaction"]
+    assert [item["description"] for item in body["items"]] == ["August transaction"]
 
 
 async def test_list_filters_by_explicit_date_range(client: AsyncClient, account_id, categories):
@@ -209,7 +229,7 @@ async def test_update_transaction_persists_changes(client: AsyncClient, account_
     resp = await client.patch(f"/transactions/{txn_id}", json={"amount": "99.99", "description": "updated"})
     assert resp.status_code == 200
     assert money(resp.json()["amount"]) == Decimal("99.99")
-    assert resp.json()["description"] == "updated"
+    assert resp.json()["description"] == "Updated"
 
     refetched = await client.get("/transactions", params={"page_size": 1})
     assert money(refetched.json()["items"][0]["amount"]) == Decimal("99.99")