fix(pen-core/variables): resolveNodeForCanvas — fontWeight + empty-vars fallback

GAP-1: add 'fontWeight' to the text-node key list in resolveNodeForCanvas so
$type-*-weight refs resolve to a number before reaching the renderer.

GAP-2: replace the early-exit `if (!variables || Object.keys(variables).length === 0)
return node` with `if (!variables) variables = {}` so DEFAULT_PALETTE_FALLBACK
fires even when the document has an empty variables map (un-seeded v1 docs).

Adds 2 new tests to fallback-equivalence.test.ts covering both gaps.

packages/pen-core/src/__tests__/fallback-equivalence.test.ts

@@ -1,5 +1,7 @@
 import { describe, it, expect } from 'vitest';
-import { resolveVariableRef } from '../variables/resolve.js';
+import { resolveVariableRef, resolveNodeForCanvas } from '../variables/resolve.js';
+import { createEmptyDocument } from '../tree-utils.js';
+import type { PenNode } from '@zseven-w/pen-types';
 
 describe('resolver-side fallback (un-seeded doc, P1.6)', () => {
   const emptyVars = {};
@@ -75,3 +77,44 @@ describe('resolver-side fallback (un-seeded doc, P1.6)', () => {
     });
   });
 });
+
+describe('GAP fixes — resolveNodeForCanvas covers all numeric refs', () => {
+  it('resolves fontWeight ref via fallback', () => {
+    const doc = createEmptyDocument();
+    const textNode: PenNode = {
+      id: 'h',
+      type: 'text',
+      name: 'H1',
+      content: 'Hello',
+      fontSize: '$type-h1-size' as unknown as number,
+      fontWeight: '$type-h1-weight' as unknown as number,
+      fill: [{ type: 'solid', color: '$color-text-primary' }],
+    };
+    const resolved = resolveNodeForCanvas(
+      textNode,
+      doc.variables ?? {},
+      undefined,
+    ) as unknown as Record<string, unknown>;
+    expect(typeof resolved.fontWeight).toBe('number');
+    expect(resolved.fontWeight).toBe(600);
+  });
+
+  it('resolves refs in empty-vars doc (fallback fires past early-exit)', () => {
+    // createEmptyDocument() returns doc.variables = undefined; passing undefined as vars
+    // exercises the GAP-2 fix (the early-exit was `if (!variables || Object.keys...)`).
+    const textNode: PenNode = {
+      id: 't',
+      type: 'text',
+      name: 'T',
+      content: 'Hi',
+      fill: [{ type: 'solid', color: '$color-text-primary' }],
+    };
+    const resolved = resolveNodeForCanvas(
+      textNode,
+      undefined as unknown as Record<string, import('@zseven-w/pen-types').VariableDefinition>,
+      undefined,
+    ) as unknown as Record<string, unknown>;
+    const fill = (resolved.fill as Array<{ type: string; color: string }>)[0];
+    expect(fill.color).toBe('#0F172A');
+  });
+});

packages/pen-core/src/variables/resolve.ts

@@ -214,7 +214,7 @@ function resolveEffectsForCanvas(
  * Returns the same object reference when no variables are present.
  */
 export function resolveNodeForCanvas(node: PenNode, variables: Vars, activeTheme?: Theme): PenNode {
-  if (!variables || Object.keys(variables).length === 0) return node;
+  if (!variables) variables = {};
 
   let changed = false;
   const out: Record<string, unknown> = { ...node };
@@ -278,7 +278,7 @@ export function resolveNodeForCanvas(node: PenNode, variables: Vars, activeTheme
   // since both paths use `node.fontSize ?? 16` (not type-guarded for strings).
   if (node.type === 'text') {
     const n = node as unknown as Record<string, unknown>;
-    for (const key of ['fontSize', 'lineHeight', 'letterSpacing'] as const) {
+    for (const key of ['fontSize', 'fontWeight', 'lineHeight', 'letterSpacing'] as const) {
       if (typeof n[key] === 'string' && isVariableRef(n[key] as string)) {
         const resolved = resolveNumericRef(n[key] as string, variables, activeTheme);
         if (resolved !== undefined) {