chore: sync from fn-registry agent

CMakeLists.txt

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+# engine_smoke — gamedev stack smoke test. Issue 0072a.
+# Standalone — does NOT use add_imgui_app() / fn_framework.
+#
+# Two build modes:
+#   1. As subdir of cpp/ (cmake -S cpp -B build): cpp/CMakeLists.txt already
+#      adds vendor/sdl3 and exposes SDL3::SDL3-static. We just link.
+#   2. As top-level (cmake -S cpp/apps/engine_smoke -B build) — used by the
+#      WASM pipeline and any standalone build. We do project() + manually
+#      add_subdirectory the vendored SDL3.
+
+cmake_minimum_required(VERSION 3.16)
+
+# Detect mode: top-level vs subdir.
+if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+    project(engine_smoke CXX)
+    set(_TOP_LEVEL TRUE)
+else()
+    set(_TOP_LEVEL FALSE)
+endif()
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_POSITION_INDEPENDENT_CODE ON)
+
+# Resolve the repo's cpp/vendor regardless of build mode.
+get_filename_component(_REPO_CPP_ROOT ${CMAKE_CURRENT_LIST_DIR}/../.. ABSOLUTE)
+set(_VENDOR ${_REPO_CPP_ROOT}/vendor)
+
+if(_TOP_LEVEL)
+    # Bring in SDL3 ourselves.
+    if(NOT EXISTS ${_VENDOR}/sdl3/CMakeLists.txt)
+        message(FATAL_ERROR "SDL3 vendoring missing: ${_VENDOR}/sdl3 — see cpp/vendor/sdl3.VENDORING.md")
+    endif()
+    set(SDL_SHARED OFF CACHE BOOL "" FORCE)
+    set(SDL_STATIC ON CACHE BOOL "" FORCE)
+    set(SDL_TEST_LIBRARY OFF CACHE BOOL "" FORCE)
+    set(SDL_TESTS OFF CACHE BOOL "" FORCE)
+    set(SDL_EXAMPLES OFF CACHE BOOL "" FORCE)
+    set(SDL_INSTALL OFF CACHE BOOL "" FORCE)
+    set(SDL_X11_XSCRNSAVER OFF CACHE BOOL "" FORCE)
+    add_subdirectory(${_VENDOR}/sdl3 ${CMAKE_BINARY_DIR}/_sdl3 EXCLUDE_FROM_ALL)
+endif()
+
+# --- ImGui (sources we need) ---
+set(_IMGUI_SRCS
+    ${_VENDOR}/imgui/imgui.cpp
+    ${_VENDOR}/imgui/imgui_demo.cpp
+    ${_VENDOR}/imgui/imgui_draw.cpp
+    ${_VENDOR}/imgui/imgui_tables.cpp
+    ${_VENDOR}/imgui/imgui_widgets.cpp
+    ${_VENDOR}/imgui/backends/imgui_impl_sdl3.cpp
+    ${_VENDOR}/imgui/backends/imgui_impl_opengl3.cpp
+)
+
+add_executable(engine_smoke
+    main.cpp
+    ${_IMGUI_SRCS}
+)
+
+target_include_directories(engine_smoke PRIVATE
+    ${_VENDOR}/imgui
+    ${_VENDOR}/sokol
+)
+
+target_link_libraries(engine_smoke PRIVATE SDL3::SDL3-static)
+
+if(NOT EMSCRIPTEN)
+    find_package(OpenGL REQUIRED)
+    target_link_libraries(engine_smoke PRIVATE OpenGL::GL)
+endif()
+
+if(EMSCRIPTEN)
+    set_target_properties(engine_smoke PROPERTIES SUFFIX ".html")
+    target_compile_options(engine_smoke PRIVATE
+        -Os
+        -fno-exceptions
+        -fno-rtti
+        -ffunction-sections
+        -fdata-sections
+    )
+    target_link_options(engine_smoke PRIVATE
+        -Os
+        -sUSE_WEBGL2=1
+        -sFULL_ES3=1
+        -sALLOW_MEMORY_GROWTH=1
+        -sINITIAL_MEMORY=33554432
+        -sASSERTIONS=0
+        -sENVIRONMENT=web
+        -Wl,--gc-sections
+        # NOTE: -sFILESYSTEM=0 + --closure=1 broke under SDL3 (closure
+        # references undeclared FS). Saves ~30KB JS + ~30KB wasm if
+        # we ever stub SDL3 filesystem refs out. Re-enable per app.
+    )
+endif()
+
+if(WIN32)
+    set_target_properties(engine_smoke PROPERTIES WIN32_EXECUTABLE TRUE)
+endif()

app.md

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+---
+name: engine_smoke
+lang: cpp
+domain: gamedev
+description: "Smoke test del stack gamedev: SDL3 + sokol_gfx + Dear ImGui. Valida que el stack compila y corre en PC (Linux/Windows desktop GL) y WASM (WebGL2 via emscripten) antes de invertir tiempo en runtime real (issue 0072a)."
+tags: [imgui, sdl3, sokol, gamedev, smoke, wasm]
+uses_functions: []
+uses_types: []
+framework: "imgui"
+entry_point: "main.cpp"
+dir_path: "cpp/apps/engine_smoke"
+repo_url: ""
+e2e_checks:
+  - id: build_pc
+    cmd: "cmake --build build --target engine_smoke -j"
+    timeout_s: 300
+  - id: smoke_self
+    cmd: "timeout 5 ./build/cpp/apps/engine_smoke/engine_smoke || test $? = 124"
+    timeout_s: 10
+    severity: warning  # requires display in CI; warning, not critical
+  - id: build_wasm
+    cmd: "bash bash/functions/pipelines/build_wasm_cpp_app.sh engine_smoke"
+    timeout_s: 600
+    severity: warning  # requires emsdk
+  - id: wasm_size_budget
+    cmd: "test -f build/wasm/engine_smoke/engine_smoke.wasm.gz && test $(stat -c%s build/wasm/engine_smoke/engine_smoke.wasm.gz) -lt 1572864"
+    severity: warning
+---
+
+# engine_smoke
+
+Primer experimento del stack gamedev (issue [0072a](../../../dev/issues/0072a-gamedev-smoke-sdl3-sokol-imgui.md)).
+
+## Que hace
+
+1. Abre ventana SDL3 1280x720 con context OpenGL.
+2. Inicializa `sokol_gfx` sobre ese context (GL 3.3 desktop, GLES3 en WASM).
+3. Pinta un fullscreen triangle con un fragment shader animado (gradient time-based).
+4. Pinta sobre eso un panel ImGui con FPS, tamaño de ventana y boton Quit.
+
+Sin `fn_framework`, sin `add_imgui_app()`. CMakeLists standalone para evitar contaminar el shell desktop hasta validar el stack.
+
+## Build PC (Linux)
+
+Desde la raiz del fn_registry:
+
+```bash
+cmake -S cpp -B build -DCMAKE_BUILD_TYPE=Release
+cmake --build build --target engine_smoke -j
+./build/cpp/apps/engine_smoke/engine_smoke
+```
+
+## Build WASM
+
+Requiere `emsdk` instalado y activado en el shell. Ver `cpp/vendor/sokol.VENDORING.md` y `bash/functions/pipelines/build_wasm_cpp_app.sh`.
+
+```bash
+bash bash/functions/pipelines/build_wasm_cpp_app.sh engine_smoke
+# Sirve build/wasm/engine_smoke/engine_smoke.html en navegador
+```
+
+Budget objetivo: gzip ≤ 1.5 MB.
+
+## Stack vendoreado
+
+- `cpp/vendor/sdl3/` — SDL3 release-3.4.8
+- `cpp/vendor/sokol/` — sokol_gfx single-header pinned commit
+- `cpp/vendor/imgui/` — ImGui 1.92.7 con backends `imgui_impl_sdl3` + `imgui_impl_opengl3`
+
+## Notas de implementacion
+
+- Fullscreen tri via `gl_VertexID` (3 vertices, no VBO). Cubre todo el viewport sin atributos.
+- Uniform `u_time` actualizado por frame.
+- Backend ImGui = `imgui_impl_opengl3` (oficial, 0 LoC custom). Compatible WebGL2 emscripten.
+- `SOKOL_GLCORE` desktop / `SOKOL_GLES3` web — selccion compile-time.
+- `setup_gfx` se llama UNA VEZ tras crear el GL context. `sg_setup` toma `sglue_environment()` que lee el contexto activo.
+
+## No-objetivos (smoke)
+
+- No texturas reales (eso entra en 0072b).
+- No audio.
+- No input game-style.
+- No fn_framework integration.
+- No mobile (Android/iOS son issues 0072g/h).

main.cpp

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+// engine_smoke — gamedev stack smoke test.
+// Validates SDL3 + sokol_gfx + Dear ImGui (imgui_impl_sdl3 + imgui_impl_opengl3)
+// builds and runs on PC (desktop GL 3.3) and WASM (WebGL2 via -sFULL_ES3=1).
+//
+// Issue 0072a. Standalone — does NOT use fn_framework / add_imgui_app.
+
+#include <cstdio>
+#include <cstdint>
+#include <cmath>
+
+#include <SDL3/SDL.h>
+
+// sokol_gfx — single TU includes the implementation.
+#define SOKOL_IMPL
+#if defined(__EMSCRIPTEN__)
+    #define SOKOL_GLES3
+#else
+    #define SOKOL_GLCORE
+#endif
+#include "sokol_gfx.h"
+#include "sokol_log.h"
+// sokol_glue.h is NOT used: it pulls in sokol_app symbols. We use SDL3 for
+// windowing, so we build sg_environment / sg_swapchain manually.
+
+#include "imgui.h"
+#include "backends/imgui_impl_sdl3.h"
+#include "backends/imgui_impl_opengl3.h"
+
+#if defined(__EMSCRIPTEN__)
+    #include <emscripten/emscripten.h>
+#endif
+
+namespace {
+
+struct App {
+    SDL_Window* win = nullptr;
+    SDL_GLContext gl = nullptr;
+    sg_pipeline pip{};
+    sg_bindings bind{};
+    sg_pass_action pass_action{};
+    bool running = true;
+    uint64_t frame = 0;
+};
+
+App g_app;
+
+// Fullscreen-quad vertex shader (no inputs, gl_VertexID trick).
+const char* VS_SRC =
+#if defined(__EMSCRIPTEN__)
+    "#version 300 es\n"
+#else
+    "#version 330 core\n"
+#endif
+    "out vec2 v_uv;\n"
+    "void main() {\n"
+    "  vec2 p = vec2((gl_VertexID == 1) ? 3.0 : -1.0, (gl_VertexID == 2) ? 3.0 : -1.0);\n"
+    "  v_uv = p * 0.5 + 0.5;\n"
+    "  gl_Position = vec4(p, 0.0, 1.0);\n"
+    "}\n";
+
+const char* FS_SRC =
+#if defined(__EMSCRIPTEN__)
+    "#version 300 es\n"
+    "precision mediump float;\n"
+#else
+    "#version 330 core\n"
+#endif
+    "in vec2 v_uv;\n"
+    "out vec4 frag;\n"
+    "uniform float u_time;\n"
+    "void main() {\n"
+    "  float r = 0.5 + 0.5 * sin(u_time + v_uv.x * 6.2831);\n"
+    "  float g = 0.5 + 0.5 * sin(u_time * 1.3 + v_uv.y * 6.2831);\n"
+    "  float b = 0.5 + 0.5 * sin(u_time * 0.7 + (v_uv.x + v_uv.y) * 6.2831);\n"
+    "  frag = vec4(r, g, b, 1.0);\n"
+    "}\n";
+
+sg_environment make_environment() {
+    sg_environment env{};
+    env.defaults.color_format = SG_PIXELFORMAT_RGBA8;
+    env.defaults.depth_format = SG_PIXELFORMAT_DEPTH_STENCIL;
+    env.defaults.sample_count = 1;
+    return env;
+}
+
+sg_swapchain make_swapchain(int w, int h) {
+    sg_swapchain sw{};
+    sw.width = w;
+    sw.height = h;
+    sw.sample_count = 1;
+    sw.color_format = SG_PIXELFORMAT_RGBA8;
+    sw.depth_format = SG_PIXELFORMAT_DEPTH_STENCIL;
+    sw.gl.framebuffer = 0;  // default framebuffer
+    return sw;
+}
+
+void setup_gfx() {
+    sg_desc d{};
+    d.environment = make_environment();
+    d.logger.func = slog_func;
+    sg_setup(&d);
+
+    sg_shader_desc sd{};
+    sd.vertex_func.source = VS_SRC;
+    sd.fragment_func.source = FS_SRC;
+    sd.uniform_blocks[0].stage = SG_SHADERSTAGE_FRAGMENT;
+    sd.uniform_blocks[0].size = sizeof(float);
+    sd.uniform_blocks[0].layout = SG_UNIFORMLAYOUT_NATIVE;
+    sd.uniform_blocks[0].glsl_uniforms[0].type = SG_UNIFORMTYPE_FLOAT;
+    sd.uniform_blocks[0].glsl_uniforms[0].glsl_name = "u_time";
+    sg_shader shd = sg_make_shader(&sd);
+
+    sg_pipeline_desc pd{};
+    pd.shader = shd;
+    pd.primitive_type = SG_PRIMITIVETYPE_TRIANGLES;
+    g_app.pip = sg_make_pipeline(&pd);
+
+    g_app.pass_action.colors[0].load_action = SG_LOADACTION_CLEAR;
+    g_app.pass_action.colors[0].clear_value = {0.05f, 0.05f, 0.08f, 1.0f};
+}
+
+void frame() {
+    SDL_Event ev;
+    while (SDL_PollEvent(&ev)) {
+        ImGui_ImplSDL3_ProcessEvent(&ev);
+        if (ev.type == SDL_EVENT_QUIT) g_app.running = false;
+        if (ev.type == SDL_EVENT_WINDOW_CLOSE_REQUESTED) g_app.running = false;
+    }
+
+    int w, h;
+    SDL_GetWindowSizeInPixels(g_app.win, &w, &h);
+
+    sg_pass p{};
+    p.action = g_app.pass_action;
+    p.swapchain = make_swapchain(w, h);
+    sg_begin_pass(&p);
+    sg_apply_pipeline(g_app.pip);
+
+    float t = (float)g_app.frame * (1.0f / 60.0f);
+    sg_range time_range{ &t, sizeof(t) };
+    sg_apply_uniforms(0, &time_range);
+
+    sg_draw(0, 3, 1);  // 3 vertices, fullscreen tri via gl_VertexID
+
+    // ImGui on top
+    ImGui_ImplOpenGL3_NewFrame();
+    ImGui_ImplSDL3_NewFrame();
+    ImGui::NewFrame();
+
+    ImGui::SetNextWindowPos(ImVec2(10, 10));
+    ImGui::Begin("engine_smoke", nullptr,
+        ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoResize |
+        ImGuiWindowFlags_AlwaysAutoResize | ImGuiWindowFlags_NoMove);
+    ImGui::Text("SDL3 + sokol_gfx + ImGui");
+    ImGui::Text("FPS: %.1f", ImGui::GetIO().Framerate);
+    ImGui::Text("Frame: %llu  Size: %dx%d", (unsigned long long)g_app.frame, w, h);
+    if (ImGui::Button("Quit")) g_app.running = false;
+    ImGui::End();
+
+    ImGui::Render();
+    ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
+
+    sg_end_pass();
+    sg_commit();
+    SDL_GL_SwapWindow(g_app.win);
+    g_app.frame++;
+}
+
+#if defined(__EMSCRIPTEN__)
+void emscripten_loop() {
+    if (!g_app.running) {
+        emscripten_cancel_main_loop();
+        return;
+    }
+    frame();
+}
+#endif
+
+}  // namespace
+
+int main(int /*argc*/, char** /*argv*/) {
+    if (!SDL_Init(SDL_INIT_VIDEO)) {
+        std::fprintf(stderr, "SDL_Init failed: %s\n", SDL_GetError());
+        return 1;
+    }
+
+#if defined(__EMSCRIPTEN__)
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
+#else
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
+#endif
+    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
+    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
+
+    g_app.win = SDL_CreateWindow("engine_smoke", 1280, 720,
+        SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_HIGH_PIXEL_DENSITY);
+    if (!g_app.win) {
+        std::fprintf(stderr, "SDL_CreateWindow failed: %s\n", SDL_GetError());
+        SDL_Quit();
+        return 1;
+    }
+    g_app.gl = SDL_GL_CreateContext(g_app.win);
+    if (!g_app.gl) {
+        std::fprintf(stderr, "SDL_GL_CreateContext failed: %s\n", SDL_GetError());
+        SDL_DestroyWindow(g_app.win);
+        SDL_Quit();
+        return 1;
+    }
+    SDL_GL_MakeCurrent(g_app.win, g_app.gl);
+    SDL_GL_SetSwapInterval(1);
+
+    setup_gfx();
+
+    IMGUI_CHECKVERSION();
+    ImGui::CreateContext();
+    ImGui::StyleColorsDark();
+    ImGui_ImplSDL3_InitForOpenGL(g_app.win, g_app.gl);
+#if defined(__EMSCRIPTEN__)
+    ImGui_ImplOpenGL3_Init("#version 300 es");
+#else
+    ImGui_ImplOpenGL3_Init("#version 330 core");
+#endif
+
+#if defined(__EMSCRIPTEN__)
+    emscripten_set_main_loop(emscripten_loop, 0, 1);
+#else
+    while (g_app.running) frame();
+#endif
+
+    ImGui_ImplOpenGL3_Shutdown();
+    ImGui_ImplSDL3_Shutdown();
+    ImGui::DestroyContext();
+    sg_shutdown();
+    SDL_GL_DestroyContext(g_app.gl);
+    SDL_DestroyWindow(g_app.win);
+    SDL_Quit();
+    return 0;
+}