`Size` can be a newtype.

[Zemyla]

The Exact and Max constructors require a nonnegative Int. Denotationally, Exact 0 is the same as Max 0. There's also unknown. This means you can fit an entire Size into the same space as an Int:

• Exact n is represented by a non-negative n.
• Max n is represented by a negative n, where n <= maxBound.
• Unknown is minBound, because minBound == negate minBound.

Doing so would allow Size to be unpacked in Bundle and various functions. Exact, Max, and Unknown can be pattern synonyms. I feel like this would improve performance somewhat.