perf(gnovm): skip store probe for synthetic package paths

[omarsy]

Summary

Every transaction's preprocessing calls evalConst, which spins up a throwaway Machine with the compiler-internal PkgPath == ".dontcare". NewMachineWithOptions then calls store.GetPackage(".dontcare", …), which fell through the per-tx object cache to a backend store read — a guaranteed miss, charged as a full I/O read of 59,000 gas, once per transaction.

Synthetic (dot-prefixed) package paths (.uverse, .dontcare, …) are never persisted and cannot appear in user source, so there is nothing in the backend to find. GetPackage now consults only the per-tx object cache for them and returns early, skipping both the backend read and the pkgGetter.

oid := ObjectIDFromPkgPath(pkgPath)
// Synthetic packages are never persisted: check only the cache — a
// backend read would be a guaranteed miss charged as a full I/O
// read, and the pkgGetter cannot resolve them either.
if IsSyntheticPath(pkgPath) {
    if oo, exists := ds.cacheObjects[oid]; exists {
        return oo.(*PackageValue)
    }
    return nil
}

A named IsSyntheticPath predicate is added alongside the existing path predicates (IsRealmPath, IsEphemeralPath, …) in mempackage.go so the convention is named rather than an inline byte check.

Impact

Every transaction is exactly 59,000 gas cheaper. Measured on the gnokey_gasfee integration flow:

tx	before	after
call Hello()	1,270,991	1,211,991
addpkg r/hello	2,815,572	2,756,572

Each affected gas golden was verified to shift by exactly −59,000 (a single avoided flat store read), confirming no other behavior changed.

Ephemeral /e/…/run paths (MsgRun) do not flow through GetPackage, so they are out of scope here.

Changed files

• Code — gnovm/pkg/gnolang/store.go (early-exit in GetPackage), gnovm/pkg/gnolang/mempackage.go (new IsSyntheticPath predicate).
• Test goldens — gno.land/pkg/integration/testdata/{gnokey_gasfee,gc,restart_gas,simulate_gas,stdlib_ibc_crypto_determinism,stdlib_restart_compare}.txtar, each −59,000 gas.

Verification

• go test ./gno.land/pkg/sdk/vm/ -run Gas ✅
• go test ./gno.land/pkg/integration/ -run TestTestdata ✅ (goldens regenerated)
• go test ./gnovm/pkg/gnolang/ -run Files -test.short ✅

🤖 Generated with Claude Code

[Gno2D2]

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