perf(vm): lazily clone the type-check cache per transaction

[omarsy]

Summary

MakeGnoTransactionStore ran maps.Clone(vm.typeCheckCache) on every transaction (via the BeginTxHook), but only AddPackage and Run ever consume that cache — MsgCall and query eval, the common case, never type-check. Every such transaction paid for a full clone of the shared cache (~stdlib package count) and discarded it unused.

This stores a small holder that clones lazily on first access instead:

type typeCheckCacheHolder struct {
    base   gno.TypeCheckCache // shared, treated as read-only
    cloned gno.TypeCheckCache // per-tx working copy; nil until first get
}

func (h *typeCheckCacheHolder) get() gno.TypeCheckCache {
    if h.cloned == nil {
        h.cloned = maps.Clone(h.base)
    }
    return h.cloned
}

Transactions that never type-check skip the clone entirely; AddPackage/Run still get exactly one clone, shared across a tx's messages.

Why it's safe (no consensus / gas / behavior change)

• Off the metered path. The clone happens before the gas meter is wired to the preprocess allocator (SetPreprocessAllocator / SetGasMeter run afterward), so it never consumed tx gas in either the old or new code. No gas goldens change.
• Single-clone-per-tx preserved. BeginTxHook fires once per transaction, so all messages in a tx share one holder → one clone, identical to the previous eager behavior.
• Isolation preserved. Each tx gets a distinct holder over a read-only base (vm.typeCheckCache, only written at init/restart); the consumer writes to the clone, never base.
• Concurrency. A holder belongs to one tx's context and, like the rest of per-tx execution (store, allocator, gas meter), assumes a single driving goroutine; documented on the type. Verified with go test -race.

Impact

Pure node-side work reduction: eliminates one maps.Clone of the shared type-check cache for every non-type-checking transaction (the majority). No user-visible or consensus-visible effect.

Changed files

• gno.land/pkg/sdk/vm/keeper.go — lazy holder + accessor (20 lines).

Verification

• go test ./gno.land/pkg/sdk/vm/ ✅
• go test -race ./gno.land/pkg/sdk/vm/ ✅
• gofmt / go vet clean

🤖 Generated with Claude Code

[Gno2D2]

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