fix(gameengine): resolve duplicate CMake preset error from stale Conan layouts

When Conan's build output layout changes (e.g. build/generators/ vs
build/Release/generators/), CMakeUserPresets.json accumulates includes
that define the same preset names, causing CMake to fail with
"Duplicate preset". The fix detects preset name collisions across
included files and keeps only the newest, in addition to pruning
missing files.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

gameengine/python/dev_commands.py

@@ -338,7 +338,14 @@ def generate(args: argparse.Namespace) -> None:
 
 
 def _fix_cmake_user_presets() -> None:
-    """Ensure CMakeUserPresets.json only includes existing preset files."""
+    """Ensure CMakeUserPresets.json only includes existing, non-conflicting preset files.
+
+    Conan regenerates preset files when the build layout changes (e.g.
+    ``build-ninja/build/generators/`` vs ``build-ninja/build/Release/generators/``).
+    If the old file still exists, CMake fails with "Duplicate preset".  This
+    function removes missing includes *and* detects preset name collisions,
+    keeping only the newest file when duplicates are found.
+    """
     import json as json_mod
     presets_path = Path("CMakeUserPresets.json")
     if not presets_path.exists():
@@ -346,11 +353,39 @@ def _fix_cmake_user_presets() -> None:
     try:
         data = json_mod.loads(presets_path.read_text())
         includes = data.get("include", [])
+
+        # Drop missing files
         valid = [p for p in includes if Path(p).exists()]
-        if len(valid) != len(includes):
+
-            data["include"] = valid
+        # Detect and resolve duplicate preset names across included files
+        seen_names: dict[str, str] = {}  # preset_name -> include_path
+        duplicates: set[str] = set()
+        for inc_path in valid:
+            try:
+                inc_data = json_mod.loads(Path(inc_path).read_text())
+            except (json_mod.JSONDecodeError, OSError):
+                continue
+            for key in ("configurePresets", "buildPresets", "testPresets"):
+                for preset in inc_data.get(key, []):
+                    name = preset.get("name", "")
+                    if name in seen_names and seen_names[name] != inc_path:
+                        # Keep the newer file, drop the older one
+                        older = seen_names[name]
+                        newer = inc_path
+                        if Path(older).stat().st_mtime > Path(newer).stat().st_mtime:
+                            older, newer = newer, older
+                        duplicates.add(older)
+                        seen_names[name] = newer
+                    else:
+                        seen_names[name] = inc_path
+
+        deduped = [p for p in valid if p not in duplicates]
+
+        if deduped != includes:
+            data["include"] = deduped
             presets_path.write_text(json_mod.dumps(data, indent=4) + "\n")
-            print(f"  Fixed CMakeUserPresets.json: kept {len(valid)}/{len(includes)} includes")
+            removed = len(includes) - len(deduped)
+            print(f"  Fixed CMakeUserPresets.json: removed {removed} stale/duplicate include(s)")
     except (json_mod.JSONDecodeError, OSError):
         pass