FortalAvatar token arithmetic produces a negative icon size

[leoafarias]

Summary

FortalAvatar cannot safely render its default icon path because the recipe multiplies an unresolved Mix numeric token reference by 0.5.

Found while validating #80 at b16636b017f3c8832d8f27f316cc24c0ad92ce8a.

Evidence

fortal_avatar_styles.dart computes:

.icon(.size(_fortalAvatarDimension(size) * 0.5))

Every _fortalAvatarDimension branch returns a numeric Fortal token reference. Mix represents unresolved double references with registered negative sentinels; arithmetic produces a new unregistered value instead of a derived token.

A focused widget test captures -5e-7 for size 2 rather than the intended 16:

testWidgets('FortalAvatar resolves a valid icon size', (tester) async {
  double? resolvedSize;

  await tester.pumpRemixApp(
    FortalAvatar(
      size: FortalAvatarSize.size2,
      icon: Icons.person,
      iconBuilder: (context, spec, icon) {
        resolvedSize = spec.size;
        return const SizedBox.shrink();
      },
    ),
  );

  expect(resolvedSize, greaterThanOrEqualTo(0)); // actual: -5e-7
});

Without iconBuilder, Icon(size: -5e-7) reaches Flutter and throws because the generated BoxConstraints has a negative minimum width/height.

This reproduces with:

• consumer Mix 2.2.0-beta.1;
• the Remix workspace override at Mix revision 07dafe904e56a9b60a172f4ef1863cf45564603a.

The same PR head contains no other Fortal recipe expression that performs arithmetic on a numeric token reference.

Expected

All Fortal avatar sizes resolve a finite, nonnegative icon size that preserves FortalThemeConfig.scaling.

Suggested direction

• Add explicit scaled avatar-icon-size tokens, or another token-preserving derived-value mechanism.
• Avoid ordinary arithmetic on unresolved sentinel-backed token references.
• Add default-icon widget coverage for every Fortal avatar size.
• Add a source/parity check that rejects numeric token arithmetic in Fortal recipes.

Acceptance criteria

• FortalAvatar(icon: ...) builds without an exception for sizes 1–9.
• Resolved icon sizes equal half of the resolved avatar dimensions at default and non-default Fortal scaling.
• The default icon path and iconBuilder receive the same valid geometry.
• A regression test fails if a token reference is arithmetically transformed before resolution.

Ownership

This is a Remix/Fortal recipe defect, not a Mix interpolation defect. Mix correctly resolves registered token references; the recipe discards that identity before resolution.

[leoafarias]

Resolved by #80 and included in merge commit 40704eb. The merged PR includes the implementation and verification for this issue. Closing as completed.