#+EXEC shapes

`#+EXEC`	ABI	invoked by	builds
`command`	argv + stdin → stdout	agent, workflow	yes
`component`	WIT-typed, in-process	component, workflow	yes
`kernel`	`bytes → bytes` hot loop	the fabric	yes
`task`	runnable recipe	agent	no
`federation`	OQL data source + sync	the query layer	mixed
`posix`	native binary	agent, workflow	no

Each shape in depth, with when to use it: The six shapes.