test(coverage): a reproducible coverage preset, report and floor check

CMakePresets.json

@@ -49,6 +49,25 @@
         "PLOT_BUILD_QT6": true,
         "PLOT_BUILD_GTK4": true
       }
+    },
+    {
+      "name": "linux-coverage",
+      "displayName": "Linux Debug (code coverage)",
+      "description": "The instrumented tree behind tools/coverage.sh: src/** compiled with --coverage -O0 -g (and linked with --coverage, so the test binary writes .gcda), built into build/cov. Adapters and examples stay off so the measurement is the library plus its unit suite and the build stays quick; PLOT_BUILD_TESTS=ON and PLOT_COVERAGE=ON are required, the latter adding the `coverage` target. Nothing here changes the other presets.",
+      "generator": "Ninja",
+      "binaryDir": "${sourceDir}/build/cov",
+      "cacheVariables": {
+        "CMAKE_BUILD_TYPE": "Debug",
+        "CMAKE_CXX_FLAGS": "--coverage -O0 -g",
+        "CMAKE_EXE_LINKER_FLAGS": "--coverage",
+        "PLOT_BUILD_TESTS": true,
+        "PLOT_COVERAGE": true,
+        "PLOT_BUILD_EXAMPLES": false,
+        "PLOT_BUILD_GLFW": false,
+        "PLOT_BUILD_IMGUI": false,
+        "PLOT_BUILD_QT6": false,
+        "PLOT_BUILD_GTK4": false
+      }
     }
   ],
   "buildPresets": [
@@ -63,6 +82,10 @@
     {
       "name": "linux-asan",
       "configurePreset": "linux-asan"
+    },
+    {
+      "name": "linux-coverage",
+      "configurePreset": "linux-coverage"
     }
   ]
 }