Shake: depend on rules from Shakefile in subdirectory?

Question

I've got a project that looks something like this:

.
├── pyproject.toml
├── server.py
├── Shakefile.hs
└── ui
   ├── index.ts
   └── Shakefile.hs

ui/Shakefile.hs contains something to the effect of:

import Development.Shake

main = shakeArgs shakeOptions $ do
  want ["dist/index.js"]

  "dist/index.js" %> \out -> do
    need ["index.ts"]
    cmd "tsc --outFile" [out]

and the root Shakefile.hs looks like:

import Development.Shake

main = shakeArgs shakeOptions $ do
  want ["dist/server.tar"]

  "dist/server.tar" %> \out -> do
    need ["ui/dist/index.js", "server.py"]
    cmd "tar cf" [out, "ui/dist/index.js", "server.py"]

Question: how should I model dist/server.tar's dependency on ui/dist/index.js?

My first guess was simply to add a rule specifying how to build ui/dist/index.html relative to the project root, with the action being to simply call shake (so that I don't have to keep the recipes in sync):

-- added to ./Shakefile.hs
"ui/dist/index.js" %> \_ -> do
  cmd "stack exec shake -- -C ui dist/index.js"

BUT, considering the Shake paper cites Recursive Make Considered Harmful, I'm near certain this isn't the way to go.

Is there a way to import rules from another Shakefile? Can vanilla Haskell's import system be used to implement something like this? In either case, how could we (automatically?) translate rules and actions using paths relative to the child directory to be correct relative to the parent?

In general, I'm wondering about Shake's applicability to monorepos, and about the composability of different Shake-based build systems (i.e. Shakefiles from different internal projects).

Thanks for your consideration!