feat(math-cuda): RPX256 permutation kernel source + host known-answer harness (lane K, phase 1)

Makefile

@@ -3,7 +3,7 @@ compile-programs compile-recursion-elfs clean-asm clean-rust clean-bench clean-s
 clean-recursion-elfs clean test test-asm \
 test-rust test-ethrex test-ethrex-offline test-executor test-syscalls test-flamegraph flamegraph-prover test-profile-recursion test-profile-recursion-single test-profile-recursion-multi \
 test-profile-recursion-block recursion-profile-block-input \
-test-fast test-prover test-prover-all test-prover-debug test-disk-spill test-math-cuda test-blake3-host-kat test-blake3-second-source test-cuda-integration test-cuda-d1 test-cuda-fallback \
+test-fast test-prover test-prover-all test-prover-debug test-disk-spill test-math-cuda test-blake3-host-kat test-rpx-host-kat test-blake3-second-source test-cuda-integration test-cuda-d1 test-cuda-fallback \
 test-prover-cuda test-prover-comprehensive-cuda \
 bench-math-cuda bench-prover bench-prover-cuda build check clippy fmt lint regen-ethrex-fixtures \
 update-ethrex-fixture-checksums check-ethrex-fixture-checksums ethrex-real-block-fixture \
@@ -621,6 +621,17 @@ test-blake3-host-kat:
 	    -o target/host_kat/blake3_host_kat_6r $(HOST_KAT_DIR)/blake3_host_kat.cpp
 	./target/host_kat/blake3_host_kat_6r
 
+# Known-answer tests for the RPX256 device kernel source, run on the HOST through
+# the Track G shim (no GPU, no nvcc): the permutation, the rate-8 overwrite-duplex
+# leaf and the parent compress against vectors printed from the Rust oracle
+# (`prover/tests/rpx_host_kat_vectors.rs`), plus miden-crypto's 19 RPO vectors
+# through the shared FB round.
+test-rpx-host-kat:
+	@mkdir -p target/host_kat
+	$(CXX) $(HOST_KAT_CXXFLAGS) \
+	    -o target/host_kat/rpx_host_kat $(HOST_KAT_DIR)/rpx_host_kat.cpp
+	./target/host_kat/rpx_host_kat
+
 # SECOND-SOURCE validation of the 6-round vectors the KAT above trusts.
 #
 # `test-blake3-host-kat` checks the KERNEL against the committed tables. This