test(bench): SponzaBench harness + #40→HEAD perf measurement (#155)

Headless benchmark around the native Sponza RT scene: times setup and a
measured Render() loop over the full multi-mesh atrium, prints BENCH
metrics, and exits. Includes run-bench.sh and a README documenting the
methodology and the measured net gain from #40 to current master.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/SponzaBench/project.cpp

@@ -0,0 +1,60 @@
+import std;
+import Crafter.Build;
+namespace fs = std::filesystem;
+using namespace Crafter;
+
+// SponzaBench — a headless benchmark harness around the native Sponza
+// ray-tracing scene. Same asset bundle and shaders as examples/Sponza,
+// but main.cpp times setup + a fixed measured frame loop instead of
+// opening an interactive window. Native (Vulkan) only — the point is to
+// measure the native renderer's per-frame and setup cost across library
+// revisions (issue #155: net perf gain from #40 to now).
+constexpr std::string_view kSponzaGitUrl    = "https://github.com/jimmiebergmann/Sponza.git";
+constexpr std::string_view kSponzaCommitSHA = "222338979d32f4f4818466291bdbc29f192b86ba";
+constexpr std::uint16_t    kAlbedoSize      = 1024u;
+
+extern "C" Configuration CrafterBuildProject(std::span<const std::string_view> args) {
+    std::vector<std::string> graphicsArgs(args.begin(), args.end());
+    Configuration* graphics = LocalProject({
+        .projectFile = "../../project.cpp",
+        .args = graphicsArgs,
+    });
+
+    Configuration cfg;
+    cfg.path = "./";
+    cfg.name = "SponzaBench";
+    cfg.outputName = "SponzaBench";
+    cfg.type = ConfigurationType::Executable;
+    ApplyStandardArgs(cfg, args);
+    cfg.dependencies = { graphics };
+
+    std::array<fs::path, 0> ifaces = {};
+    std::array<fs::path, 1> impls = { "main" };
+    cfg.GetInterfacesAndImplementations(ifaces, impls);
+
+    fs::path sponzaRoot = GitFetch({
+        .url    = std::string(kSponzaGitUrl),
+        .commit = std::string(kSponzaCommitSHA),
+    });
+    std::string bundleKey = std::format("{}|{}", kSponzaCommitSHA, kAlbedoSize);
+    auto bundleHash = std::hash<std::string>{}(bundleKey);
+    fs::path bundleDir = fs::path("build") / std::format("sponza-bundle-{:016x}", bundleHash);
+
+    if (auto err = BuildOBJBundle(
+            sponzaRoot / "sponza.obj",
+            sponzaRoot / "sponza.mtl",
+            bundleDir,
+            kAlbedoSize); !err.empty()) {
+        std::println(std::cerr, "Sponza bundle error: {}", err);
+        std::exit(1);
+    }
+
+    for (const auto& entry : fs::directory_iterator(bundleDir)) {
+        if (entry.is_regular_file()) cfg.files.push_back(entry.path());
+    }
+
+    cfg.shaders.emplace_back(fs::path("raygen.glsl"),     std::string("main"), ShaderType::RayGen);
+    cfg.shaders.emplace_back(fs::path("closesthit.glsl"), std::string("main"), ShaderType::ClosestHit);
+    cfg.shaders.emplace_back(fs::path("miss.glsl"),       std::string("main"), ShaderType::Miss);
+    return cfg;
+}