fix: prevent rich inline CJK fragments from overflowing maxWidth

src/layout.test.ts

@@ -735,6 +735,60 @@ describe('rich-inline invariants', () => {
       )
     }
   })
+
+  test('CJK inline-rich items do not overflow maxWidth', () => {
+    // Regression test for https://github.com/chenglou/pretext/issues/120
+    // When CJK text is split across multiple rich inline items, the
+    // line-break engine's "always place at least one unit" guarantee can
+    // push a line past maxWidth if the rich inline stepper doesn't guard
+    // against overflow when starting a new item mid-line.
+    const maxWidth = 100
+    const prepared = prepareRichInline([
+      { text: '你好世界测试', font: FONT },
+      { text: '引号里的重点', font: FONT },
+      { text: '和括号里的补充', font: FONT },
+    ])
+
+    const lines: Array<{ width: number }> = []
+    walkRichInlineLineRanges(prepared, maxWidth, range => {
+      const line = materializeRichInlineLineRange(prepared, range)
+      lines.push({ width: line.width })
+    })
+
+    expect(lines.length).toBeGreaterThan(0)
+    for (const line of lines) {
+      expect(line.width).toBeLessThanOrEqual(maxWidth + 0.5) // allow lineFitEpsilon
+    }
+
+    // Also verify stats path stays consistent
+    const stats = measureRichInlineStats(prepared, maxWidth)
+    expect(stats.lineCount).toBe(lines.length)
+    expect(stats.maxLineWidth).toBeLessThanOrEqual(maxWidth + 0.5)
+  })
+
+  test('CJK inline-rich items with inter-item gap do not overflow', () => {
+    // CJK items separated by whitespace-only items (collapsed to gaps)
+    const maxWidth = 80
+    const prepared = prepareRichInline([
+      { text: '测试文本 ', font: FONT },
+      { text: ' 中文排版', font: FONT },
+      { text: ' 溢出修复', font: FONT },
+    ])
+
+    const lines: Array<{ width: number }> = []
+    walkRichInlineLineRanges(prepared, maxWidth, range => {
+      const line = materializeRichInlineLineRange(prepared, range)
+      lines.push({ width: line.width })
+    })
+
+    expect(lines.length).toBeGreaterThan(0)
+    for (const line of lines) {
+      expect(line.width).toBeLessThanOrEqual(maxWidth + 0.5)
+    }
+
+    const stats = measureRichInlineStats(prepared, maxWidth)
+    expect(stats.lineCount).toBe(lines.length)
+  })
 })
 
 describe('layout invariants', () => {

src/rich-inline.ts

@@ -319,6 +319,20 @@ function stepRichInlineLine(
       continue
     }
 
+    // Guard against overflow: stepPreparedLineGeometry always places at
+    // least one content unit even when it exceeds maxWidth (to prevent
+    // infinite loops in standalone layout). When we already have content on
+    // the current line and the returned fragment would push us past
+    // safeWidth, break the line before this item so the fragment can start
+    // fresh on the next line where it will have the full width available.
+    if (
+      lineWidth > 0 &&
+      atItemStart &&
+      gapBefore + lineWidthForItem + item.extraWidth > remainingWidth
+    ) {
+      break lineLoop
+    }
+
     // If the only thing we can fit after paying the boundary gap is a partial
     // slice of the item's first segment, prefer wrapping before the item so we
     // keep whole-word-style boundaries when they exist. But once the current
@@ -469,6 +483,15 @@ function stepRichInlineLineStats(
       continue
     }
 
+    // Guard against overflow (mirrors the check in stepRichInlineLine)
+    if (
+      lineWidth > 0 &&
+      atItemStart &&
+      gapBefore + lineWidthForItem + item.extraWidth > remainingWidth
+    ) {
+      break lineLoop
+    }
+
     if (
       lineWidth > 0 &&
       atItemStart &&