Prefer fork-choice finalized checkpoint; add test

CMakeLists.txt

@@ -197,8 +197,21 @@ if(LANTERN_BUILD_TESTS)
     target_link_libraries(lantern_client_state_staleness_test PRIVATE lantern)
     add_test(NAME lantern_client_state_staleness COMMAND lantern_client_state_staleness_test)
 
-    add_executable(lantern_genesis_anchor_test tests/unit/test_genesis_anchor.c)
+    add_executable(lantern_genesis_anchor_test
+        tests/unit/test_genesis_anchor.c
+        tests/unit/client_test_helpers.c
+    )
     target_link_libraries(lantern_genesis_anchor_test PRIVATE lantern)
+    target_include_directories(
+        lantern_genesis_anchor_test
+        PRIVATE
+            ${PROJECT_SOURCE_DIR}/tests/unit
+    )
+    target_compile_definitions(
+        lantern_genesis_anchor_test
+        PRIVATE
+            LANTERN_TEST_FIXTURE_DIR="${PROJECT_SOURCE_DIR}/tests/fixtures"
+    )
     add_test(NAME lantern_genesis_anchor COMMAND lantern_genesis_anchor_test)
 
     add_executable(lantern_genesis_bootstrap_test tests/unit/test_genesis_bootstrap.c)

src/core/client_http.c

@@ -615,6 +615,15 @@ int http_finalized_state_ssz_cb(void *context, uint8_t **out_bytes, size_t *out_
     }
 
     LanternCheckpoint finalized = client->state.latest_finalized;
+    if (client->has_fork_choice)
+    {
+        const LanternCheckpoint *fork_finalized =
+            lantern_fork_choice_latest_finalized(&client->fork_choice);
+        if (fork_finalized && !lantern_root_is_zero(&fork_finalized->root))
+        {
+            finalized = *fork_finalized;
+        }
+    }
     lantern_client_unlock_state(client, state_locked);
 
     if (lantern_root_is_zero(&finalized.root))

src/core/client_reqresp.c

@@ -1083,6 +1083,15 @@ int reqresp_build_status(void *context, LanternStatusMessage *out_status)
     }
 
     out_status->finalized = client->state.latest_finalized;
+    if (client->has_fork_choice)
+    {
+        const LanternCheckpoint *fork_finalized =
+            lantern_fork_choice_latest_finalized(&client->fork_choice);
+        if (fork_finalized && !lantern_root_is_zero(&fork_finalized->root))
+        {
+            out_status->finalized = *fork_finalized;
+        }
+    }
 
     bool head_set = false;
     if (client->has_fork_choice)

src/core/client_sync_blocks.c

@@ -1544,7 +1544,16 @@ static bool rebuild_state_for_root_locked(
     LanternRoot replay_stop_root = {0};
     char replay_stop_hex[ROOT_HEX_BUFFER_LEN] = {0};
 
-    if (client->has_state)
+    if (client->has_fork_choice)
+    {
+        const LanternCheckpoint *fork_finalized =
+            lantern_fork_choice_latest_finalized(&client->fork_choice);
+        if (fork_finalized)
+        {
+            replay_stop_root = fork_finalized->root;
+        }
+    }
+    else if (client->has_state)
     {
         replay_stop_root = client->state.latest_finalized.root;
     }