Add undo/redo/reset chain to useUpdateFragment

[jho406]

useUpdateFragment currently fires and forgets — once you update a fragment, there's no way to walk it back without manually dispatching the previous state. This makes optimistic UI patterns tedious.

Proposed API

update() returns a chainable object with the fragment bound and an internal undo/redo stack:

const update = useUpdateFragment()

// Chain multiple updates
const cart = update(cartRef, (draft) => { draft.quantity = 5 })
  .update((draft) => { draft.quantity = 10 })
  .update((draft) => { draft.color = 'red' })

// Walk backward/forward
cart.undo()  // back to q=10
cart.undo()  // back to q=5
cart.redo()  // forward to q=10

// Discard everything this chain did
cart.reset() // back to state before the chain started

Behavior

• The first call update(ref, updater) binds the fragment and starts the chain
• Each method returns a new chain object with the stack curried in
• Every update, undo, redo, and reset dispatches updateFragment immediately
• undo() at the bottom of the stack is a no-op (no dispatch)
• redo() at the top of the stack is a no-op (no dispatch)
• update() after undo() clears the redo stack (standard undo/redo semantics)
• reset() restores the state from before the chain started and clears the stack

Use case: optimistic UI

const update = useUpdateFragment()
const cart = update(cartRef, (draft) => { draft.items.push(item) })

try {
  await remote('/cart', { method: 'POST', body: item })
} catch {
  cart.reset()
}

Getting started

git checkout v2
cd superglue/superglue
npm install
npx vitest run spec/lib/useSetFragment.spec.jsx # existing tests

When opening your PR, target the v2 branch.

[jho406]

I'm happy to take just a reset for starters. That would have value on its own, great for when a fetch fails.