docs: what the hard memory limit counts on each system

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/native-client.md

@@ -271,6 +271,11 @@ process: on a clean launch this build commits 1.1 to 1.2 GB before a world is op
 the game's resources), so a budget under about 1.4 GB leaves too little to run, exactly as `-Xmx` too
 low throws `OutOfMemoryError`.
 
+What "committed" means depends on the system. On Windows it is the process's commit charge, the
+figure Task Manager shows, the graphics driver's pages included. On Linux and macOS there is no such
+figure: it is what the game's allocator (mimalloc) committed, so the driver's and the GPU's own memory
+are outside the budget there.
+
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