cevm: bind to the clean unversioned C ABI, drop the compat shim

The Go bindings called gpu_execute_block_v4 / gpu_free_result_v2, which
luxcpp/cevm main does not export — it renamed those to gpu_execute_block /
gpu_free_result. A luxd built CGO_ENABLED=1 against the shipped libs would have
failed to link, not merely mismatched a version. It stayed hidden because
production builds pure-Go and this box had stale branch-built libs installed.

cevm_v4compat.h and cevm_abi_v4compat_cgo.go existed only to bridge that gap —
113 lines whose own comment described the header and library being out of step.
Deleted; cgo already includes the library header directly.

ABIVersion is now taken from that header (C.EVM_GPU_ABI_VERSION) instead of a
hand-maintained Go constant that had drifted to 7 while the header said 6. One
definition, so the two cannot disagree; a runtime panic no longer has to catch
what the compiler can.

go vet clean; ./evm/cevm and ./evm/cevm/parallel both pass.

Co-authored-by: Hanzo Dev <[email protected]>

evm/cevm/cevm.go

@@ -205,7 +205,7 @@ type BlockContext struct {
 // the GPU a state snapshot (account nonce, balance, code, code_hash) so
 // the kernel CALL/CREATE path resolves targets on-device instead of
 // returning CallNotSupported. V3 callers still see the same wire shape.
-const ABIVersion uint32 = 6
+//
 
 // StateAccount is one entry in the snapshot of touched accounts handed to
 // ExecuteBlockV4. Fields mirror the C-side CGpuStateAccount byte-for-byte

evm/cevm/cevm_cgo.go

@@ -52,6 +52,10 @@ func AutoDetect() Backend {
 // module's expected ABIVersion. A mismatch means the binary and the cevm
 // module were built against incompatible C++ headers and any execution would
 // produce silently wrong results — fail fast at process start instead.
+// ABIVersion is the ABI this build was compiled against, taken from the
+// library's own header. There is no second copy to keep in sync.
+const ABIVersion = uint32(C.EVM_GPU_ABI_VERSION)
+
 func init() {
 	got := uint32(C.gpu_abi_version())
 	if got != ABIVersion {
@@ -262,7 +266,7 @@ func ExecuteBlockV4(backend Backend, numThreads uint32, txs []Transaction, ctx *
 		}
 	}
 
-	result := C.gpu_execute_block_v4(
+	result := C.gpu_execute_block(
 		&ctxs[0],
 		C.uint32_t(len(ctxs)),
 		C.uint8_t(backend),
@@ -274,7 +278,7 @@ func ExecuteBlockV4(backend Backend, numThreads uint32, txs []Transaction, ctx *
 		codePtr,
 		C.uint32_t(codeSize),
 	)
-	defer C.gpu_free_result_v2(&result)
+	defer C.gpu_free_result(&result)
 	runtime.KeepAlive(ctxs)
 	runtime.KeepAlive(cctxStorage)
 	runtime.KeepAlive(cAccts)

evm/cevm/cevm_nocgo.go

@@ -2,6 +2,9 @@
 
 package cevm
 
+// No library linked, so there is no ABI to report.
+const ABIVersion uint32 = 0
+
 import "fmt"
 
 // AutoDetect returns CPUSequential when built without CGo.