feat: probe Vulkan loader boundary

fixtures/acceptance/coverage.tsv

@@ -26,6 +26,8 @@ S0-VK-002	covered	cargo test -p fparkan-render-vulkan --offline device_scoring_i
 S0-VK-003	covered	cargo test -p fparkan-render-vulkan --offline portability_subset_is_reported_and_enabled_when_exposed
 S0-VK-004	covered	cargo test -p fparkan-render-vulkan --offline rejects_missing_graphics_present_swapchain_and_format
 S0-VK-005	covered	cargo test -p fparkan-render-vulkan --offline capability_report_json_is_stable
+S0-VK-006	covered	cargo test -p fparkan-render-vulkan --offline loader_probe_report_json_is_stable
+S0-VK-007	covered	cargo xtask policy
 S0-LIMIT-001	covered	cargo test -p fparkan-binary --offline rejects_count_stride_overflow
 S0-LIMIT-002	covered	cargo test -p fparkan-binary --offline rejects_oversized_declared_allocation_before_read
 L1-P1-NRES-001	covered	cargo test -p fparkan-nres --offline licensed_corpora_nres_roundtrip_gates