Fix inflated word spacing in PDF description text

writeDescription/emitBlocks rendered each word as a separately positioned
Tj, advancing by our approximate average-glyph-width estimate — which is
much wider than real space/character widths, producing "This  is  bold"
style gaps. Render each line as one continuous text object instead
(PdfBuilder.textRun), so consecutive Tj operators advance using the
viewer's real font metrics.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

core/pdf.js

@@ -102,6 +102,35 @@ class PdfBuilder {
     );
   }
 
+  /**
+   * Render a line made of mixed-font/color segments (e.g. bold/italic runs)
+   * as one continuous text object: consecutive Tj operators without an
+   * intervening Tm advance the cursor by each font's real glyph widths, so
+   * spacing matches the viewer's metrics exactly (unlike our approximate
+   * textWidth(), which is only used for word-wrap decisions).
+   */
+  textRun(parts, x, yTop, size) {
+    const y = this.pageHeight - yTop - size;
+    const ops = [`BT 1 0 0 1 ${x.toFixed(2)} ${y.toFixed(2)} Tm`];
+    let curFont = null;
+    let curColor = null;
+    for (const part of parts) {
+      if (!part.text) continue;
+      if (part.font !== curFont) {
+        ops.push(`/${part.font} ${size} Tf`);
+        curFont = part.font;
+      }
+      if (!curColor || part.color[0] !== curColor[0] || part.color[1] !== curColor[1] || part.color[2] !== curColor[2]) {
+        ops.push(`${col(part.color)} rg`);
+        curColor = part.color;
+      }
+      const clean = String(part.text).replace(/\t/g, '    ');
+      ops.push(`(${esc(toLatin1(clean))}) Tj`);
+    }
+    ops.push('ET');
+    this.currentPage.ops.push(ops.join(' '));
+  }
+
   rect(x, yTop, w, h, { fill = null, stroke = null, lineWidth = 1 } = {}) {
     const y = this.pageHeight - yTop - h;
     const ops = [];

exporters/pdf.js

@@ -148,12 +148,12 @@ function exportPdf(ast, outDir, template = {}) {
         ensure(item.lineHeight);
         const textX = M + indentBase + item.indent;
         if (idx === 0 && item.prefix) pdf.text(item.prefix, textX - LIST_INDENT, y, { size: item.size, font: 'F1', color });
-        let x = textX;
-        for (const word of line) {
-          const c = word.href ? tpl.accentColor : (item.muted ? [100, 100, 100] : color);
-          pdf.text(word.text, x, y, { size: item.size, font: word.font, color: c });
-          x += pdf.textWidth(word.text, item.size, word.font);
-        }
+        const parts = line.map((word) => ({
+          text: word.text,
+          font: word.font,
+          color: word.href ? tpl.accentColor : (item.muted ? [100, 100, 100] : color),
+        }));
+        pdf.textRun(parts, textX, y, item.size);
         y += item.lineHeight;
       });
       y += 4;
@@ -271,12 +271,12 @@ function exportPdf(ast, outDir, template = {}) {
         item.lines.forEach((line, idx) => {
           const textX = M + 10 + item.indent;
           if (idx === 0 && item.prefix) pdf.text(item.prefix, textX - LIST_INDENT, by, { size: item.size, font: 'F1' });
-          let x = textX;
-          for (const word of line) {
-            const c = word.href ? tpl.accentColor : (item.muted ? [100, 100, 100] : [0, 0, 0]);
-            pdf.text(word.text, x, by, { size: item.size, font: word.font, color: c });
-            x += pdf.textWidth(word.text, item.size, word.font);
-          }
+          const parts = line.map((word) => ({
+            text: word.text,
+            font: word.font,
+            color: word.href ? tpl.accentColor : (item.muted ? [100, 100, 100] : [0, 0, 0]),
+          }));
+          pdf.textRun(parts, textX, by, item.size);
           by += item.lineHeight;
         });
         by += 4;