First attempt at cutting down the amount of recompiles for the tools, but maybe I just have meson only build the tool when I run it?

meson.build

@@ -105,7 +105,7 @@ executable('zedcaster',
   dependencies: dependencies)
 
 executable('arena',
-  sources + [ 'tools/arena.cpp' ],
+  arena_sources + [ 'tools/arena.cpp' ],
   cpp_args: cpp_args,
   link_args: link_args,
   include_directories: inc_dirs,

src/meson.build

@@ -66,3 +66,57 @@ sources = files(
   # root
   'dbc.cpp',
 )
+
+arena_sources = files(
+  # ai
+  'ai/ai.cpp',
+  'ai/ai_debug.cpp',
+  'ai/goap.cpp',
+
+  # combat
+  'combat/battle.cpp',
+  'combat/combat.cpp',
+
+  # boss fight mini game
+  'boss/fight.cpp',
+  'boss/system.cpp',
+  'boss/ui.cpp',
+
+  # gui
+  'gui/backend.cpp',
+  'gui/combat_ui.cpp',
+  'gui/debug_ui.cpp',
+  'gui/event_router.cpp',
+  'gui/guecstra.cpp',
+
+  # graphics
+  'graphics/animation.cpp',
+  'graphics/camera.cpp',
+  'graphics/easing.cpp',
+  'graphics/palette.cpp',
+  'graphics/scene.cpp',
+  'graphics/shaders.cpp',
+  'graphics/textures.cpp',
+  'graphics/lights.cpp',
+
+  # algos
+  'algos/matrix.cpp',
+  'algos/maze.cpp',
+  'algos/spatialmap.cpp',
+  'algos/rand.cpp',
+  'algos/pathing.cpp',
+
+  # game
+  'game/worldbuilder.cpp',
+  'game/map.cpp',
+  'game/level.cpp',
+  'game/inventory.cpp',
+  'game/sound.cpp',
+  'game/systems.cpp',
+  'game/components.cpp',
+  'game/config.cpp',
+  'game/rituals.cpp',
+
+  # root
+  'dbc.cpp',
+)