CardDb: make loadCard idempotent (fix latent duplicate-PaperCard bug)

[shoeless]

Problem

CardDb.loadCard is not idempotent: addSetCard unconditionally increments the art index and appends a fresh PaperCard. A redundant call for a (name, set) printing that's already loaded therefore duplicates that PaperCard in allCardsByName.

Fix

Skip when that exact (name, set) printing already exists, via a new side-effect-free hasPrintingInSet check. Guarding on card-name presence alone would break the "add a printing from a not-yet-loaded set" path (StaticData.getOrLoadCommonCard), where the card can already exist under other sets while the requested set's printing is still missing — so the guard is keyed on the specific edition.

Why "any printing present" is a safe guard despite multi-printing sets

A set can contain multiple printings of the same name (CardEdition.getCardInSet returns a List<EditionEntry> — basic-land arts, showcase variants; that's what artIndex is for). The guard is still sound because loadCard is all-or-nothing per (name, set): addFromSetByName loops over every EditionEntry of that name in the set and addSetCards each one. addSetCard has exactly two callers — that loop, and the eager full-set path in initialize — so no code path ever adds a subset of a name's printings for a set. Any-printing-present therefore implies the (name, set) load already ran, art variants included. (Entries excluded by the functional-variant filter are excluded on every call equally, so the invariant holds.)

Single file, forge-core only.

🤖 Generated with Claude Code

[Hanmac]

artIndex is on my list to be removed anyway

I just need to find a better way to rename the image files #7771

[shoeless]

Good to know — this guard doesn't lean on artIndex, only on loadCard adding all of a (name, set)'s printings in one call, so it should carry over cleanly (or simplify) when artIndex goes away with #7771.

Pushed a small hardening while re-checking it: the existing-printing check now also matches the card's rules name, since a lookup name can be shared across different cards (CopyFaceFrom alt faces, flavor names) — no stock data hits that today, but custom content could.

To be clear, the duplication itself isn't artIndex's doing — allCardsByName is an ArrayList-backed multimap and nothing in the add path checks for an existing entry, so a redundant call appends regardless; artIndex only determines how the duplicates are labeled. The guard becomes droppable once that rework makes the add path uniqueness-enforcing.