Wow it sure gets defensive about how it figures out the context size…
(Was using gemini-flash-2.5-preview)
tl,dr: {context_size} was working because this particular keyword seemed to be a read-only property that’s provided by Cursor.
It kinda-sorta is inconvenient that {javascriptFunctions()} were interpolated inside the quasi-XML/YAML format of the rule too – and this too was codegen-ed.
Everything above with a grain of 
since it’s questionable halulu.
I think I hit the fourth wall…