cmd/keeper: export getInput in wasm builds (#33686)

This is a tweak to the wasm build, that expects the `geth_io` namespace
to expect a `geth_io` module, providing a `len` and `read` methods. This
will be provided by the WASM interface in sp1. This forces an API change
on the OpenVM side, but the interface on their side is still being
designed, so we should proceed with this change, and we'll make a
different tag for OpenVM if this can't work for them.

Co-authored-by: wakabat <wakabat@protonmail.com>

cmd/keeper/getpayload_wasm.go

@@ -0,0 +1,36 @@
+// Copyright 2026 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+//go:build wasm
+// +build wasm
+
+package main
+
+import (
+	"unsafe"
+)
+
+//go:wasmimport geth_io len
+func hintLen() uint32
+
+//go:wasmimport geth_io read
+func hintRead(data unsafe.Pointer)
+
+func getInput() []byte {
+	data := make([]byte, hintLen())
+	hintRead(unsafe.Pointer(&data[0]))
+	return data
+}

cmd/keeper/stubs.go

@@ -14,7 +14,8 @@
 // You should have received a copy of the GNU Lesser General Public License
 // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
 
-//go:build !example && !ziren
+//go:build !example && !ziren && !wasm
+// +build !example,!ziren,!wasm
 
 package main