Is it possible to combine multiple subnodes into a fat node?

[waterlens]

I'm trying to draw a diagram similar to this one:

My plan is to regard it as separate 4 nodes which are close enough together.
However, I found it hard to specify the distance between nodes in fletcher because I cannot directly get the size of a node.
And I don't know if I can let all nodes share the same height automatically.
Is it possible to add support to such a diagram, through a new concept of fat nodes and subnodes in fletcher?

Currently, I can get a scribbled diagram using fletcher,

with this code:

#import "@preview/fletcher:0.4.4" as fletcher: diagram, node, edge, draw

#let debug = if false { 2 } else { 0 }

#let nodeshape(node, extrude, fradius: x => x + 3pt) = {
	let (w, h) = node.size.map(i => i/2 + extrude)
	draw.rect(
		(-w, -h), (+w, +h),
		radius: fradius(extrude),
	)
}

#let lnodeshape = nodeshape.with(fradius: extrude => (north-west: extrude + 3pt, south-west: extrude + 3pt))
#let mnodeshape = nodeshape.with(fradius: extrude => 0pt)
#let rnodeshape = nodeshape.with(fradius: extrude => (north-east: extrude + 3pt, south-east: extrude + 3pt))

#let mydiagram = diagram.with(
  debug: debug,
  spacing: (10mm, 5mm),
  node-stroke: 1pt,
  edge-stroke: 1pt,
  mark-scale: 60%
)

#let node0 = node((0, 0), `Left`, shape: lnodeshape)
#let node1 = node((0.63, 0), `Right`, shape: rnodeshape)

#mydiagram(
  node0,
  node1,
)

[Jollywatt]

You could try making the composite node one node with a table as content. This solution still requires you to manually position edges, but that's easier than manually joining nodes.

#import "@preview/fletcher:0.4.4" as fletcher: diagram, node, edge, draw

#let label = table(
  columns: (12mm, 4mm, 4mm, 4mm),
  `Node`, none, `4`, none,
  stroke: (x, y) => if 0 < x and x < 3 { (x: 1pt) },
)

#diagram(
  node-stroke: 1pt,
  edge-stroke: 1pt,
  mark-scale: 50%,
  node((0,0), label, inset: 0pt, corner-radius: 3pt),
  edge((0.09,0), (0,1), "*-straight", snap-to: ((99,99), auto)),
  edge((0.41,0), (1,1), "*-straight", snap-to: ((99,99), auto)),
  node((0,1), `Subnode`),
)

I've used snap-to to prevent the edges from snapping to the composite node. (Surprisingly, passing none to snap-to doesn'y work — I'll fix that — so I gave it coordinates of a nonexistent node instead.)

It would be really cool to support something like pinit for doing something like this more automatically, though.

[Jollywatt]

@waterlens I'm going to assume that the table-in-a-node trick worked fine, so that we don't need to add a new kind of 'fat' node or 'subnode' :)