dgb: wire M3 RPC guard tests into ctest + CI allowlist

Register the three standalone M3 regression guards
(rpc_request_test / softfork_check_test / genesis_check_test) as ctest
targets in src/impl/dgb/test/CMakeLists.txt and add them to BOTH
build.yml --target allowlists. Header-only: each links only GTest +
nlohmann_json (no OBJECT lib), so they stay buildable while the
external-daemon transport rpc.cpp wiring remains deferred (Option-B).

Avoids the #143 NOT_BUILT trap: a gtest target present in CMake but
absent from the build.yml allowlist becomes a NOT_BUILT sentinel that
reds master. Both lists, always.

23/23 guard assertions pass (rpc-request 8, softfork 8, genesis 7).

Author: frstrtr

.github/workflows/build.yml

@@ -68,6 +68,7 @@ jobs:
                     test_mweb_builder \
                     test_address_resolution test_compute_share_target \
                     test_utxo test_dgb_subsidy dgb_share_test \
+                    rpc_request_test softfork_check_test genesis_check_test \
                     v37_test \
             -j$(nproc)
 
@@ -195,6 +196,7 @@ jobs:
                     test_mweb_builder \
                     test_address_resolution test_compute_share_target \
                     test_utxo test_dgb_subsidy dgb_share_test \
+                    rpc_request_test softfork_check_test genesis_check_test \
                     test_coin_broadcaster test_multiaddress_pplns test_pplns_stress \
                     v37_test \
             -j$(nproc)

src/impl/dgb/test/CMakeLists.txt

@@ -16,4 +16,19 @@ if (BUILD_TESTING AND GTest_FOUND)
     include(GoogleTest)
     include_directories(${gtest_SOURCE_DIR}/include ${gtest_SOURCE_DIR})
     gtest_add_tests(dgb_share_test "" AUTO)
+
+    # --- M3 RPC-transport standalone regression guards ---------------------
+    # Header-only guards over the external-daemon RPC coin-layer SSOTs
+    # (rpc_request.hpp request-shape + version floor + genesis identity, and
+    # softfork_check.hpp softfork-name collection). They link no OBJECT lib —
+    # only GTest + nlohmann_json — so they stay buildable even while the
+    # transport rpc.cpp wiring is deferred (Option-B scope). Each MUST appear
+    # in BOTH this ctest registration AND the build.yml --target allowlist,
+    # or it becomes a #143-style NOT_BUILT sentinel that reds master.
+    foreach(dgb_guard rpc_request_test softfork_check_test genesis_check_test)
+        add_executable(${dgb_guard} ${dgb_guard}.cpp)
+        target_link_libraries(${dgb_guard} PRIVATE
+            GTest::gtest_main GTest::gtest nlohmann_json::nlohmann_json)
+        gtest_add_tests(${dgb_guard} "" AUTO)
+    endforeach()
 endif()