4.0.0 fails current nightly: mutable bindings lack $ prefixes

Summary

roc-lang/unicode 4.0.0 fails under nightly-2026-09-08-39a3f89
because mutable bindings in the released package do not use the new $
naming convention.

This is not specific to roc bundle: checking a consumer's source package
directly reproduces it.

Reproduction

Using the 4.0.0 package dependency:

{ unicode: "https://github.com/roc-lang/unicode/releases/download/4.0.0/3DGC3M4b2pxaRLg4i8cmxWkm2E2WbCPCLntQzf2mkbUV.tar.zst" }

and Roc nightly-2026-09-08-39a3f89, run against roc-pdf commit
c365811bd3dfbf835379a8ad914fa60a683da07d:

roc check package/main.roc

Actual result

The command reports 171 diagnostics and exits with status 2. Examples include:

var name missing '$' .../Bidi.roc:104:7
var output = []

var name missing '$' .../ScriptItemization.roc:203:7
var state = initial

The same diagnostics break ordinary source validation and the release-bundle
consumer test.

Expected result

The released unicode package checks successfully with the current nightly. Its
mutable bindings should use $-prefixed names, followed by a new package
release for consumers to pin.

Downstream evidence

• Initial nightly updater run: https://github.com/lukewilliamboswell/roc-pdf/actions/runs/34256023551
• Candidate release validation: https://github.com/lukewilliamboswell/roc-pdf/actions/runs/34331598811
• Candidate PR: https://github.com/lukewilliamboswell/roc-pdf/pull/28

I also inspected the archive produced by roc bundle: roc-pdf's existing
var $name bindings retain their $ prefixes. The failing files are from the
downloaded unicode 4.0.0 package, not rewritten roc-pdf modules.