Modernize retained Linux WebGL CMake baselines

docs/modernization/build-inventory.md

@@ -17,8 +17,8 @@ Keep it updated as platform paths move to shared CMake targets.
 | Android standard | `android/android/build.gradle`, `android/android/CMakeLists.txt` | Retained native library target `native-lib`; CMake 3.10/C++23 baseline now links the standard arm64 package path with modern component/service sources and the generated `nanort` overlay helper |
 | Android Quest | `android/quest/build.gradle`, `android/quest/CMakeLists.txt` | OVR SDK imported libraries; CMake 3.10/C++23 baseline and current Yoga source list configure with the shared Android package compatibility helper |
 | Android Focus/Wave | `android/focus/build.gradle`, `android/focus/CMakeLists.txt` | Wave SDK imported libraries; CMake 3.10/C++23 baseline and current Yoga source list configure with the shared Android package compatibility helper |
-| Linux | `linux/CMakeLists.txt` | Old CMake 3.4, C++14 flag |
-| WebGL/Emscripten | `webgl/CMakeLists.txt` | Old CMake 3.4, WebGL2 flags |
+| Linux | `linux/CMakeLists.txt` | Retained app target now uses CMake 3.10 and target-level C++23 while package/root target migration remains open |
+| WebGL/Emscripten | `webgl/CMakeLists.txt` | Retained WebGL app target now uses CMake 3.10 and target-level C++23 with retained WebGL2/Emscripten link flags |
 
 ## Existing Version Generation
 
@@ -211,6 +211,11 @@ powershell -ExecutionPolicy Bypass -File scripts\automation\apple-remote-build.p
   `panopainter_platform_build_apple_remote`. These targets call the existing
   platform automation scripts from CMake and keep platform validation discoverable
   from the CMake target graph while app/package target migration remains open.
+- Retained Linux and WebGL app CMake entrypoints are still separate from root
+  CMake, but now share the modernization baseline of CMake 3.10 and
+  target-level `cxx_std_23`. `panopainter_retained_platform_cmake_self_test`
+  guards those baselines until these entrypoints are replaced by shared root
+  CMake package/app targets.
 - Root CMake exposes named `fuzz` and `stress` CTest presets. `fuzz` currently
   runs deterministic parser/serializer edge tests for binary streams, image
   metadata, PPI, stroke scripts, and layout XML; `stress` currently runs the

docs/modernization/roadmap.md

@@ -1412,6 +1412,11 @@ checks: `panopainter_package_readiness`,
 `panopainter_android_native_package_smoke`. App/package entrypoints still need
 to consume shared targets and remain covered by debt until package validation
 is migrated from legacy package projects to root CMake.
+Retained Linux and WebGL app CMake entrypoints now match the interim platform
+baseline used by Android package paths: CMake 3.10 plus target-level
+`cxx_std_23`, with `panopainter_retained_platform_cmake_self_test` guarding
+against regressions while those entrypoints wait behind root CMake package/app
+target migration.
 Apple compile validation now runs on the local Mac mini SSH host
 `panopainter-mac` through `scripts/automation/apple-remote-build.ps1`. The host
 uses Homebrew CMake/Ninja/Git plus full Xcode via `DEVELOPER_DIR`, pulls the
@@ -2413,6 +2418,11 @@ Results:
   panopainter_windows_app_package_smoke`, which builds the CMake `PanoPainter`
   app target, validates the executable/runtime `data/` copy, and reports the
   still-blocked Windows AppX package state.
+- Retained Linux and WebGL app CMake files now use CMake 3.10 and target-level
+  C++23 instead of global C++14 flags; `python
+  scripts/dev/check_retained_platform_cmake.py` and CTest
+  `panopainter_retained_platform_cmake_self_test` guard those baselines while
+  the actual Linux/WebGL app/package targets remain outside root CMake.
 - Root CMake now exposes platform validation targets for the default headless
   platform-build sweep, the Android standard/Quest/Focus root CMake asset
   component sweep, the vcpkg-backed UI core dependency boundary, and the

linux/CMakeLists.txt

@@ -1,7 +1,5 @@
-cmake_minimum_required(VERSION 3.4.1)
-project(panopainter)
-
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++14")
+cmake_minimum_required(VERSION 3.10)
+project(PanoPainterLinux LANGUAGES C CXX)
 
 add_executable(panopainter
 	src/main.cpp
@@ -120,4 +118,7 @@ target_include_directories(panopainter PRIVATE
 )
 
 target_link_libraries(panopainter glfw curl GL dl X11 pthread)
+target_compile_features(panopainter PRIVATE cxx_std_23)
+set_target_properties(panopainter PROPERTIES
+    CXX_EXTENSIONS OFF)
 target_compile_definitions(panopainter PUBLIC "$<$<CONFIG:DEBUG>:_DEBUG>")

scripts/dev/check_retained_platform_cmake.py

@@ -0,0 +1,61 @@
+#!/usr/bin/env python3
+"""Guard retained non-root platform CMake files during Phase 6 migration."""
+
+from __future__ import annotations
+
+import json
+import re
+import sys
+from pathlib import Path
+
+
+RETAINED_PLATFORM_CMAKE = [
+    Path("linux/CMakeLists.txt"),
+    Path("webgl/CMakeLists.txt"),
+]
+
+
+def repo_root() -> Path:
+    return Path(__file__).resolve().parents[2]
+
+
+def cmake_minimum_version(text: str) -> tuple[int, ...] | None:
+    match = re.search(r"cmake_minimum_required\s*\(\s*VERSION\s+([0-9.]+)", text, re.I)
+    if not match:
+        return None
+    return tuple(int(part) for part in match.group(1).split("."))
+
+
+def main() -> int:
+    root = repo_root()
+    results: dict[str, object] = {}
+    ok = True
+
+    for path in RETAINED_PLATFORM_CMAKE:
+        text = (root / path).read_text(encoding="utf-8")
+        minimum_version = cmake_minimum_version(text)
+        has_target_cxx23 = "target_compile_features(panopainter PRIVATE cxx_std_23)" in text
+        has_cxx_extensions_off = "CXX_EXTENSIONS OFF" in text
+        uses_global_cxx_standard_flag = bool(re.search(r"-std=c\+\+14|-std=c\+\+17|-std=c\+\+20", text))
+        platform_ok = (
+            minimum_version is not None
+            and minimum_version >= (3, 10)
+            and has_target_cxx23
+            and has_cxx_extensions_off
+            and not uses_global_cxx_standard_flag
+        )
+        ok = ok and platform_ok
+        results[str(path)] = {
+            "ok": platform_ok,
+            "minimumVersion": ".".join(str(part) for part in minimum_version) if minimum_version else None,
+            "hasTargetCxx23": has_target_cxx23,
+            "hasCxxExtensionsOff": has_cxx_extensions_off,
+            "usesGlobalCxxStandardFlag": uses_global_cxx_standard_flag,
+        }
+
+    print(json.dumps({"ok": ok, "platforms": results}, separators=(",", ":")))
+    return 0 if ok else 1
+
+
+if __name__ == "__main__":
+    sys.exit(main())

tests/CMakeLists.txt

@@ -15,6 +15,11 @@ add_test(NAME panopainter_package_smoke_readiness_self_test
 set_tests_properties(panopainter_package_smoke_readiness_self_test PROPERTIES
     LABELS "tooling;desktop-fast")
 
+add_test(NAME panopainter_retained_platform_cmake_self_test
+    COMMAND "${Python3_EXECUTABLE}" "${PROJECT_SOURCE_DIR}/scripts/dev/check_retained_platform_cmake.py")
+set_tests_properties(panopainter_retained_platform_cmake_self_test PROPERTIES
+    LABELS "tooling;desktop-fast")
+
 add_library(pp_test_harness INTERFACE)
 target_include_directories(pp_test_harness INTERFACE
     "${CMAKE_CURRENT_SOURCE_DIR}")

webgl/CMakeLists.txt

@@ -1,5 +1,5 @@
-cmake_minimum_required(VERSION 3.4.1)
-project(panopainter)
+cmake_minimum_required(VERSION 3.10)
+project(PanoPainterWebGL LANGUAGES C CXX)
 file(COPY ../data
     DESTINATION ${CMAKE_CURRENT_BINARY_DIR})
 add_executable(panopainter 
@@ -103,8 +103,10 @@ add_executable(panopainter
     ../src/node_shorcuts.cpp
     ../src/node_metadata.cpp
 )
-target_compile_options(panopainter PRIVATE -std=c++14 -O3)
+target_compile_options(panopainter PRIVATE -O3)
+target_compile_features(panopainter PRIVATE cxx_std_23)
 set_target_properties(panopainter PROPERTIES 
+    CXX_EXTENSIONS OFF
     SUFFIX ".html"
     RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/html"
     LINK_FLAGS "\