refactor: split the Deck response contract from its detail view

[lesnik512]

Problem

One Deck schema served two endpoints with different card-loading strategies, leaking the difference into the type:

class Deck(DeckBase):
    id: PositiveInt
    cards: list[Card] | None

• get_deck → fetch_with_cards (selectinload) → cards populated.
• list_decks / create_deck / update_deck → relationship is lazy="noload", so .cards returns [] without loading.

So list_decks reported cards: [] for every deck even when the deck has cards — the list contract was lying. The | None was also dead: noload yields [], never None.

Change

Split the one schema into two:

class Deck(DeckBase):
    """Light deck view for lists and writes; cards are not loaded."""
    id: PositiveInt

class DeckWithCards(Deck):
    """Deck detail view; cards are eager-loaded (selectinload) and always present."""
    cards: list[Card]

• get_deck → DeckWithCards (cards always present, non-optional)
• list_decks → Decks (Collection[Deck]), create_deck / update_deck → Deck

Each endpoint's return type now states exactly what it loads. The dead | None is gone. The two-shape convention is documented in CLAUDE.md (Conventions) and in docstrings on the schemas.

Contract change ⚠️

Intentional: the cards key disappears from list / create / update responses (they never loaded cards anyway). get_deck is unchanged. Any client reading cards off a list response is affected.

Tests

test_get_one_deck locks DeckWithCards (asserts cards); list/create/update tests never asserted cards, so they stay green. 19 passed, 100% coverage.

🤖 Generated with Claude Code