fix(tools): set_font_range now produces valid style runs

- Use applyStyleToRange from text/style-runs.ts instead of naively
  appending runs (which created overlaps and invalid state)
- Apply fontWeight from style name (e.g. 'Bold' → 700)
- Apply color as fills on the style override
- Previously the color param was accepted but silently ignored

Fixes #214

packages/core/src/tools/modify.ts

@@ -1,9 +1,11 @@
 /* eslint-disable max-lines -- property setters share common patterns, splitting would scatter related tools */
 import { parseColor } from '../color'
 import { DEFAULT_SHADOW_COLOR } from '../constants'
+import { styleToWeight } from '../text/fonts'
+import { applyStyleToRange } from '../text/style-runs'
 import { defineTool } from './schema'
 
-import type { CharacterStyleOverride, Effect, SceneNode, StyleRun } from '../scene-graph'
+import type { CharacterStyleOverride, Effect, SceneNode } from '../scene-graph'
 import type { Matrix } from '../types'
 
 export const setFill = defineTool({
@@ -487,18 +489,21 @@ export const setFontRange = defineTool({
   execute: (figma, args) => {
     const node = figma.getNodeById(args.id)
     if (!node) return { error: `Node "${args.id}" not found` }
-    const style: CharacterStyleOverride = {}
-    if (args.family) style.fontFamily = args.family
-    if (args.size) style.fontSize = args.size
-    if (args.style === 'italic' || args.style === 'Italic') style.italic = true
-    const run: StyleRun = {
-      start: args.start,
-      length: args.end - args.start,
-      style
+    const override: CharacterStyleOverride = {}
+    if (args.family) override.fontFamily = args.family
+    if (args.size) override.fontSize = args.size
+    if (args.style) {
+      const s = args.style.toLowerCase()
+      if (s.includes('italic')) override.italic = true
+      override.fontWeight = styleToWeight(args.style)
     }
-    figma.graph.updateNode(node.id, {
-      styleRuns: [...(figma.graph.getNode(node.id)?.styleRuns ?? []), run]
-    })
+    if (args.color) {
+      override.fills = [{ type: 'SOLID', color: parseColor(args.color), opacity: 1, visible: true }]
+    }
+    const raw = figma.graph.getNode(node.id)
+    if (!raw) return { error: `Node "${args.id}" not found` }
+    const runs = applyStyleToRange(raw.styleRuns, args.start, args.end, override, raw.text.length)
+    figma.graph.updateNode(node.id, { styleRuns: runs })
     return { id: args.id, range: { start: args.start, end: args.end } }
   }
 })

tests/engine/tools.test.ts

@@ -542,6 +542,47 @@ describe('set_constraints', () => {
   })
 })
 
+describe('set_font_range', () => {
+  test('applies font style to text range and survives serialization', () => {
+    const { figma, graph } = setup()
+    const createText = ALL_TOOLS.find((t) => t.name === 'create_shape')!
+    const setText = ALL_TOOLS.find((t) => t.name === 'set_text')!
+    const setFontRange = ALL_TOOLS.find((t) => t.name === 'set_font_range')!
+
+    const created = createText.execute(figma, { type: 'TEXT', x: 0, y: 0, width: 200, height: 20 }) as any
+    setText.execute(figma, { id: created.id, text: 'Hello World' })
+    setFontRange.execute(figma, { id: created.id, start: 0, end: 5, family: 'Inter', size: 18, style: 'Bold' })
+
+    const node = graph.getNode(created.id)!
+    expect(node.styleRuns.length).toBeGreaterThan(0)
+    for (const run of node.styleRuns) {
+      expect(run.style).toBeDefined()
+      expect(typeof run.start).toBe('number')
+      expect(typeof run.length).toBe('number')
+    }
+    const boldRun = node.styleRuns.find((r) => r.style.fontWeight === 700)
+    expect(boldRun).toBeDefined()
+    expect(boldRun!.start).toBe(0)
+    expect(boldRun!.length).toBe(5)
+  })
+
+  test('applies color to text range', () => {
+    const { figma, graph } = setup()
+    const createText = ALL_TOOLS.find((t) => t.name === 'create_shape')!
+    const setText = ALL_TOOLS.find((t) => t.name === 'set_text')!
+    const setFontRange = ALL_TOOLS.find((t) => t.name === 'set_font_range')!
+
+    const created = createText.execute(figma, { type: 'TEXT', x: 0, y: 0, width: 200, height: 20 }) as any
+    setText.execute(figma, { id: created.id, text: 'Red text' })
+    setFontRange.execute(figma, { id: created.id, start: 0, end: 3, color: '#ff0000' })
+
+    const node = graph.getNode(created.id)!
+    const colorRun = node.styleRuns.find((r) => r.style.fills?.length)
+    expect(colorRun).toBeDefined()
+    expect(colorRun!.style.fills![0].color.r).toBeCloseTo(1)
+  })
+})
+
 describe('render', () => {
   test('renders JSX string', async () => {
     const { figma } = setup()