fix(make-pdf): Liberation Sans font fallback for Linux rendering

On Linux (Docker, CI, servers), neither Helvetica nor Arial exist. Our CSS
stacks were falling through to DejaVu Sans — wider letterforms that look like
Verdana, not the intended Helvetica/Faber look. Liberation Sans is the standard
metric-compatible Arial clone (SIL OFL 1.1, apt package fonts-liberation).

- print-css.ts: all four font stacks (body + @top-center + @bottom-center +
  @bottom-right CONFIDENTIAL) gain "Liberation Sans" between Helvetica and
  Arial. File-header docblock updated to reflect the new stack.
- .github/docker/Dockerfile.ci: explicit apt-get install fonts-liberation +
  fontconfig with retry, fc-cache -f, and a verify step that fails the build
  loud if the font disappears. Playwright's install-deps happens to pull this
  in today but the dep is implicit and could silently regress.
- SKILL.md.tmpl: one-sentence note pointing Linux users at fonts-liberation.
- SKILL.md: regenerated via bun run gen:skill-docs --host all (only make-pdf's
  generated file changed — verified clean diff scope).
- render.test.ts: 2 assertions — Liberation Sans in body stack AND in at least
  one @page margin-box rule (proves all four intended stacks got touched, not
  just one).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

make-pdf/SKILL.md

@@ -470,6 +470,10 @@ left-aligned body, Helvetica throughout, curly quotes and em dashes, optional
 cover page and clickable TOC, diagonal DRAFT watermark when you need it.
 Copy-paste from the PDF produces clean words, never "S a i l i n g".
 
+On Linux, install `fonts-liberation` for correct rendering — Helvetica and Arial
+aren't present by default, and Liberation Sans is the standard metric-compatible
+fallback. CI and Docker builds install it automatically via Dockerfile.ci.
+
 ## MAKE-PDF SETUP (run this check BEFORE any make-pdf command)
 
 ```bash

make-pdf/SKILL.md.tmpl

@@ -39,6 +39,10 @@ left-aligned body, Helvetica throughout, curly quotes and em dashes, optional
 cover page and clickable TOC, diagonal DRAFT watermark when you need it.
 Copy-paste from the PDF produces clean words, never "S a i l i n g".
 
+On Linux, install `fonts-liberation` for correct rendering — Helvetica and Arial
+aren't present by default, and Liberation Sans is the standard metric-compatible
+fallback. CI and Docker builds install it automatically via Dockerfile.ci.
+
 {{MAKE_PDF_SETUP}}
 
 ## Core patterns

make-pdf/src/print-css.ts

@@ -5,8 +5,11 @@
  * Mirror those CSS rules here. The HTML references were approved via
  * /plan-design-review with explicit design decisions locked in the plan:
  *
- *   - Helvetica only (system font, no bundled webfonts — dodges the
- *     per-glyph Tj bug that breaks copy-paste extraction).
+ *   - Helvetica first, with Liberation Sans as a metric-compatible Linux
+ *     fallback (Helvetica and Arial aren't installed on most Linux distros;
+ *     Liberation Sans ships via the fonts-liberation package and Playwright's
+ *     install-deps). No bundled webfonts — dodges the per-glyph Tj bug that
+ *     breaks copy-paste extraction.
  *   - All paragraphs flush-left. No first-line indent, no justify, no
  *     p+p indent. text-align: left everywhere. 12pt margin-bottom.
  *   - Cover page has the same 1in margins as every other page. No flexbox
@@ -15,8 +18,8 @@
  *   - `@page :first` suppresses running header/footer but does NOT override
  *     the 1in margin.
  *   - No <link>, no external CSS/fonts — everything inlined.
- *   - CJK fallback: Helvetica, Arial, Hiragino Kaku Gothic ProN, Noto Sans
- *     CJK JP, Microsoft YaHei, sans-serif.
+ *   - CJK fallback: Helvetica, Liberation Sans, Arial, Hiragino Kaku Gothic
+ *     ProN, Noto Sans CJK JP, Microsoft YaHei, sans-serif.
  */
 
 export interface PrintCssOptions {
@@ -81,13 +84,13 @@ function pageRules(size: string, margin: string, opts: PrintCssOptions): string
     `  size: ${size};`,
     `  margin: ${margin};`,
     runningHeader
-      ? `  @top-center { content: "${runningHeader}"; font-family: Helvetica, Arial, sans-serif; font-size: 9pt; color: #666; }`
+      ? `  @top-center { content: "${runningHeader}"; font-family: Helvetica, "Liberation Sans", Arial, sans-serif; font-size: 9pt; color: #666; }`
       : ``,
     showPageNumbers
-      ? `  @bottom-center { content: counter(page) " of " counter(pages); font-family: Helvetica, Arial, sans-serif; font-size: 9pt; color: #666; }`
+      ? `  @bottom-center { content: counter(page) " of " counter(pages); font-family: Helvetica, "Liberation Sans", Arial, sans-serif; font-size: 9pt; color: #666; }`
       : ``,
     showConfidential
-      ? `  @bottom-right { content: "CONFIDENTIAL"; font-family: Helvetica, Arial, sans-serif; font-size: 8pt; color: #aaa; letter-spacing: 0.05em; }`
+      ? `  @bottom-right { content: "CONFIDENTIAL"; font-family: Helvetica, "Liberation Sans", Arial, sans-serif; font-size: 8pt; color: #aaa; letter-spacing: 0.05em; }`
       : ``,
     `}`,
     ``,
@@ -104,7 +107,7 @@ function rootTypography(): string {
   return [
     `html { lang: en; }`,
     `body {`,
-    `  font-family: Helvetica, Arial, "Hiragino Kaku Gothic ProN", "Noto Sans CJK JP", "Microsoft YaHei", sans-serif;`,
+    `  font-family: Helvetica, "Liberation Sans", Arial, "Hiragino Kaku Gothic ProN", "Noto Sans CJK JP", "Microsoft YaHei", sans-serif;`,
     `  font-size: 11pt;`,
     `  line-height: 1.5;`,
     `  color: #111;`,

make-pdf/test/render.test.ts

@@ -326,6 +326,23 @@ describe("printCss", () => {
     const css = printCss({ pageNumbers: true });
     expect(css).toMatch(/@bottom-center\s*\{\s*content:\s*counter\(page\)/);
   });
+
+  test("font stacks include Liberation Sans adjacent to Helvetica", () => {
+    const css = printCss({ confidential: true });
+    // Body stack
+    expect(css).toMatch(/font-family:\s*Helvetica,\s*"Liberation Sans",\s*Arial/);
+    // At least one @page margin box (running header / page number / CONFIDENTIAL)
+    // should also have the updated stack.
+    const marginBoxStacks = css.match(/@(top|bottom)-(center|right)\s*\{[^}]*Liberation Sans/g) ?? [];
+    expect(marginBoxStacks.length).toBeGreaterThanOrEqual(1);
+  });
+
+  test("all four original Helvetica stacks now include Liberation Sans", () => {
+    const css = printCss({ runningHeader: "Running Title", confidential: true });
+    // Count: body (1) + running header (1) + page numbers (1) + confidential (1) = 4
+    const occurrences = (css.match(/"Liberation Sans"/g) ?? []).length;
+    expect(occurrences).toBeGreaterThanOrEqual(4);
+  });
 });
 
 // ─── render() — pageNumbers / footerTemplate data flow ───────────────