mix format with canonical_tailwind is not idempotent. A single pass does not produce stable output; running mix format --check-formatted immediately after mix format reports additional changes needed.

Steps to reproduce

1. Configure canonical_tailwind per the README
2. Have a file containing e.g. class="h-[48px] w-[48px] flex items-center"
3. Run mix format
4. Run mix format --check-formatted

Step 4 fails, reporting the file needs further formatting.

What happens

Pass 1 sorts the classes (reordering h-[48px] and w-[48px] to be adjacent). Pass 2 then sees them adjacent and collapses to the shorthand (size-[48px]). A single pass doesn't do both.

Observed shorthand collapses that only appear on a second pass:

• h-[48px] w-[48px] -> size-[48px]
• px-[1.2rem] py-[1.2rem] -> p-[1.2rem]
• h-[1.8rem] w-[1.8rem] -> size-[1.8rem]

Why this matters

This breaks CI. The standard Phoenix workflow runs mix format --check-formatted in CI to verify formatting. If a single mix format pass doesn't converge, CI will always fail.

Environment

• canonical_tailwind 0.1.0
• tailwindcss CLI 4.2.2
• Elixir 1.19.5 / OTP 28
• Phoenix LiveView 1.1.27