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+# Monospace Font Embedding + Naming Differentiation
+
+**Date:** 2026-07-22
+**Branch:** react-electron
+**Goal:** Bring `react-electron` to feature parity with `master` by porting the v4.5.0 "embedded monospace font" feature, and differentiate the dev build identity from the installed `markdown-converter` deb so the two can coexist on the same machine.
+
+---
+
+## Context
+
+The `react-electron` branch is the active development branch — a major rewrite of the renderer in React 19 + TypeScript + Tailwind/shadcn while keeping the main process in CommonJS. As of commit `bb4e874` it is **ahead** of `master` in nearly every dimension (auto-updater, crash writer, migration runner, command palette, first-run wizard, updates settings, crash report modal, 30+ React modals, large-file mode, scoped CSS).
+
+A repo-wide diff (`git diff --stat master..react-electron`) shows 301 files changed, +38,293/-26,786 lines. Master is **behind** react-electron.
+
+The **only** feature present in `master` and absent in `react-electron` is the monospace-font-embedding feature added in master v4.5.0 (commits `3f8679c` through `b218c76`, 19 commits). It bundles JetBrains Mono + Fira Code TTFs and embeds them into PDF/DOCX/EPUB/HTML exports so ASCII art and code blocks render with the exact font the user sees in the preview.
+
+A second concern: the user has `markdown-converter` installed as a `.deb`. Running `npm run dev` from this repo currently uses the same `appId` (`com.concreteinfo.markdownconverter`) and `productName` (`MarkdownConverter`), which triggers Electron's single-instance lock and confuses file-association routing. We rename this branch's identity to `Markdown Converter React` / `markdown-converter-react` to coexist.
+
+---
+
+## Scope
+
+### In scope
+
+1. Port the monospace font embedding feature from `master` v4.5.0 into the react-electron branch:
+   - All five `src/main/*.js` modules (`MonospaceFontConfig`, `PdfFontHeader`, `DocxFontEmbedder`, `EpubFontEmbedder`, `ExportCss`)
+   - Settings schema module (`src/main/settings/monospaceSettings.js`)
+   - Two new IPC handlers (`get-monospace-settings`, `set-monospace-settings`) plus preload allowlist and TypeScript declaration
+   - Renderer body-class toggle and CSS tokens (`--font-mono-active`, `--font-mono-feature`)
+   - Bundled font assets: `JetBrainsMono-{Regular,Bold}.ttf`, `FiraCode-{Regular,Bold}.ttf` plus LICENSE files
+   - `asarUnpack` directive for `assets/fonts/**`
+   - `download-tools.js` extension to fetch Fira Code
+   - Wire `buildMonospaceExportCss`, `buildPdfFontHeader`, `DocxFontEmbedder.embed`, `EpubFontEmbedder.embed` into `src/main/index.js` export pipelines (PDF, DOCX, EPUB, HTML paths)
+   - Print-preview font integration (`src/renderer/components/preview/PrintPreviewFrame.tsx` or equivalent)
+   - Tests: one test file per new module mirroring master's coverage plus an E2E smoke test
+
+2. Rename branch identity:
+   - `package.json` `name` → `markdown-converter-react`
+   - `package.json` `build.productName` → `Markdown Converter React`
+   - `package.json` `build.appId` → `com.concreteinfo.markdownconverter.react`
+   - `package.json` `build.linux.executableName` → `markdown-converter-react`
+   - Window title prefix → `Markdown Converter — React Dev` in dev mode (use `process.env.VITE_DEV_SERVER_URL` as the gate)
+   - Settings file path remains `userData/settings.json` (no migration needed) — but add a new key `appVariant: "react"` so the renderer can show the correct title
+
+### Out of scope
+
+- React renderer rewrites (already ahead of master)
+- Auto-updater, crash, migration (already ahead of master)
+- Tauri / Web migration
+- Pandoc version bump
+- Documentation beyond this spec, the implementation plan, and the changelog entry
+- Changes to v4-to-v5 settings migration (we leave the existing runner alone)
+
+---
+
+## Design
+
+### Module layout (new files)
+
+```
+src/main/
+  MonospaceFontConfig.js          # path resolver — finds bundled TTF
+  PdfFontHeader.js                # builds .tex fontspec header for xelatex/lualatex
+  DocxFontEmbedder.js             # injects TTF into pandoc DOCX output (post-process)
+  EpubFontEmbedder.js             # EPUB --epub-embed-font + manifest patch
+  ExportCss.js                    # builds CSS string with woff2 embedded as base64
+  settings/
+    monospaceSettings.js          # schema, defaults, family map
+  ipc/
+    monospace-handlers.js         # IPC handler registration
+  utils/
+    (existing)                    # no change
+
+src/renderer/
+  hooks/
+    use-monospace-classes.ts      # toggles body.mono-{jetbrains,fira}{,-ligatures} classes
+  components/preview/
+    PrintPreviewFrame.tsx         # wire print preview to monospace settings via IPC
+  styles/globals.css              # add --font-mono-active/--font-mono-feature declarations
+  types/electron.d.ts             # extend ElectronAPI with monospace.{getSettings,saveSettings}
+
+src/preload.js                    # add monospace channels to ALLOWED_SEND_CHANNELS + expose on window.electronAPI.monospace
+
+assets/fonts/
+  JetBrainsMono-Regular.ttf       # bundled, ~270 KB
+  JetBrainsMono-Bold.ttf          # bundled, ~278 KB
+  JetBrainsMono-LICENSE.txt
+  FiraCode-Regular.ttf            # bundled, ~300 KB
+  FiraCode-Bold.ttf               # bundled, ~300 KB
+  FiraCode-LICENSE.txt
+
+scripts/download-tools.js         # extend to fetch Fira Code
+
+tests/
+  unit/main/monospace/
+    MonospaceFontConfig.test.js
+    monospaceSettings.test.js
+    PdfFontHeader.test.js
+    DocxFontEmbedder.test.js
+    EpubFontEmbedder.test.js
+    ExportCss.test.js
+    monospace-handlers.test.js
+  smoke-e2e-monospace.js          # e2e: convert ASCII-art Markdown → PDF/DOCX/EPUB/HTML, assert TTF references appear in output
+```
+
+### Key interfaces (TypeScript-style for clarity)
+
+```ts
+// src/main/settings/monospaceSettings.js
+type MonoFont = 'jetbrains-mono' | 'fira-code';
+const FAMILY_BY_KEY: Record<MonoFont, string> = {
+  'jetbrains-mono': 'JetBrains Mono',
+  'fira-code': 'Fira Code',
+};
+function getActiveMonoFont(settings): string;
+function isLigaturesEnabled(settings): boolean;
+function safeMonospaceSettings(input): { monospaceFont: MonoFont; monospaceLigatures: boolean };
+
+// src/main/MonospaceFontConfig.js
+function getMonoFontTtfPath(familyKey, weight = 400): string | null;  // null if asset missing
+function ligaturesEnabled(settings): boolean;
+function getActiveFamily(settings): string;
+
+// src/main/PdfFontHeader.js
+function buildPdfFontHeader(settings, ttfPath, fontFamily): { headerPath: string; familyName: string };
+
+// src/main/DocxFontEmbedder.js
+async function embedDocxFont(inputDocxPath, outputDocxPath, ttfPath, fontFamily): Promise<void>;
+async function buildDocxWithEmbeddedFont(pandocArgs, settings): Promise<{args, postProcess}>;
+
+// src/main/EpubFontEmbedder.js
+async function embedEpubFont(epubPath, ttfPath, fontFamily): Promise<void>;
+function withEpubEmbedFontArgs(pandocArgs, ttfPath, fontFamily): string[];
+
+// src/main/ExportCss.js
+function buildExportCss(settings, { woff2Base64, family, ligatures }): string;
+function buildFontFaceBlock(familyKey, woff2Base64): string;
+
+// src/main/ipc/monospace-handlers.js
+function register({ getMainWindow }): void;
+//   ipcMain.handle('get-monospace-settings', () => ({ monospaceFont, monospaceLigatures }))
+//   ipcMain.handle('set-monospace-settings', (_e, partial) => safeMonospaceSettings(partial) → persist + broadcast)
+```
+
+### Renderer integration
+
+- `use-monospace-classes.ts` hook runs once on mount, calls `electronAPI.monospace.getSettings()`, applies `document.body.classList` of:
+  - `mono-jetbrains-mono` | `mono-fira-code`
+  - `mono-ligatures-on` | `mono-ligatures-off`
+- CSS in `globals.css`:
+  ```css
+  :root {
+    --font-mono-active: 'JetBrains Mono', 'SF Mono', Monaco, 'Courier New', monospace;
+    --font-mono-feature: 'liga' 0, 'calt' 0;
+  }
+  body.mono-fira-code { --font-mono-active: 'Fira Code', 'JetBrains Mono', 'SF Mono', monospace; }
+  body.mono-ligatures-on { --font-mono-feature: 'liga' 1, 'calt' 1; }
+  ```
+- All existing `font-family: monospace` and `font-family: var(--font-mono)` usages continue to work; the new tokens sit above them.
+
+### Wiring into export pipelines
+
+In `src/main/index.js` `exportWithPandoc` (PDF branch):
+- Read `monospaceFont` + `monospaceLigatures` from settings
+- Resolve TTF path via `MonospaceFontConfig.getMonoFontTtfPath`
+- If path exists: build font header via `PdfFontHeader.buildPdfFontHeader`, pass `--include-in-header=…`
+- If path missing: log warning, fall back to existing `-V monofont=Consolas` behavior
+
+In DOCX branch: invoke `DocxFontEmbedder.embedDocxFont` post-pandoc.
+In EPUB branch: prepend `--epub-embed-font=…` to pandoc args; call `EpubFontEmbedder.embedEpubFont` to patch manifest.
+In HTML branch: write CSS via `ExportCss.buildExportCss` (embed woff2 as base64) and reference in `<style>`.
+
+### Naming differentiation
+
+`package.json` changes:
+```diff
+- "name": "markdown-converter"
++ "name": "markdown-converter-react"
+- "productName": "MarkdownConverter"
++ "productName": "Markdown Converter React"
+- "appId": "com.concreteinfo.markdownconverter"
++ "appId": "com.concreteinfo.markdownconverter.react"
++ "linux": {
++   "executableName": "markdown-converter-react",
++   "synopsis": "Markdown editor (React build)",
++   "description": "Markdown editor and universal file converter — React build"
++ }
+```
+
+`src/main/window/index.js`:
+```js
+const isDev = !!process.env.VITE_DEV_SERVER_URL;
+const titleSuffix = isDev ? ' — React Dev' : '';
+mainWindow = new BrowserWindow({
+  title: `Markdown Converter${titleSuffix}`,
+  ...
+});
+```
+
+### Settings impact
+
+Add two keys to `migration-transform.js` v5 schema with safe defaults:
+- `monospaceFont: z.enum(['jetbrains-mono', 'fira-code']).default('jetbrains-mono')`
+- `monospaceLigatures: z.boolean().default(false)`
+- `appVariant: z.enum(['classic', 'react']).default('react')`
+
+Existing user settings remain valid; the migration just fills in the new defaults.
+
+---
+
+## Testing strategy (TDD)
+
+For each new module: red-green-refactor.
+
+1. `MonospaceFontConfig.test.js` — uses tmpdir + mocked `process.resourcesPath` to assert resolution from `assets/fonts/JetBrainsMono-Regular.ttf`. Covers missing-file fallback.
+2. `monospaceSettings.test.js` — schema validation: rejects unknown fonts, coerces ligatures boolean, fills defaults.
+3. `PdfFontHeader.test.js` — writes a temp `.tex` file, asserts `\setmonofont{JetBrainsMono-Regular.ttf}[...]` lines match.
+4. `DocxFontEmbedder.test.js` — given a minimal DOCX zip, asserts `word/fonts/` contains the TTF and `word/_rels/fontTable.xml.rels` references it.
+5. `EpubFontEmbedder.test.js` — asserts `META-INF/container.xml` and `content.opf` updated after `--epub-embed-font`.
+6. `ExportCss.test.js` — base64 round-trip: `atob(css.match(/base64,([A-Za-z0-9+/=]+)/)[1])` returns the original woff2 bytes.
+7. `monospace-handlers.test.js` — invokes the registered handlers against `ipcMain` mock; asserts settings persistence + broadcast.
+8. `smoke-e2e-monospace.js` — runs `pandoc` end-to-end against a fixture markdown with ASCII art; greps output for font references.
+
+Coverage threshold maintained: jest at 15%, vitest at v8 + renderer lines.
+
+---
+
+## Risks
+
+- **TTF download license** — Fira Code is OFL-1.1; JetBrains Mono is OFL-1.1. Both allow redistribution; LICENSE files ship alongside TTFs. No risk.
+- **Pandoc version sensitivity** — `--epub-embed-font` requires pandoc ≥ 2.19. The download-tools script pins to 3.9.0.2; check `pandocVersion` and gracefully fall back if older.
+- **asarUnpack size** — adding ~1.2 MB of TTFs to packaged builds. Acceptable; matches master.
+- **Dev/prod appId split** — if a user installs both `markdown-converter` and `markdown-converter-react` debs, their settings files are separate (`userData/com.concreteinfo.markdownconverter.react/settings.json`). Documented in README.
+- **Test environment** — the e2e smoke test requires pandoc available locally. We'll `test.skip` if `which pandoc` fails.
+
+---
+
+## Definition of done
+
+- [ ] All planned steps implemented, not just the first/easiest ones
+- [ ] No forbidden markers (`TODO`, `FIXME`, `XXX`, `HACK`, `not implemented`, `placeholder`, `stub`, `coming soon`) in changed source
+- [ ] New test suites pass; existing 638 tests still pass
+- [ ] `npm run build:linux` produces a `.deb` artifact named `markdown-converter-react_*_amd64.deb`
+- [ ] App launches in dev mode with title `Markdown Converter — React Dev`
+- [ ] E2E smoke test confirms TTF references in PDF/DOCX/EPUB/HTML output
+- [ ] CHANGELOG.md updated with a "5.1.0 — react-electron parity" entry
+- [ ] No unrelated refactors; every changed line traces to the request
+
+---
+
+## Learning collaboration
+
+Per the project's learning-mode preference, the user will be asked to contribute two 5-10 line decisions during implementation:
+
+1. **Default monospace family** in `monospaceSettings.js` (`jetbrains-mono` vs `fira-code` vs `system-fallback`).
+2. **Body-class gating strategy** in `use-monospace-classes.ts` (apply on every settings change vs debounce vs once-on-mount).
+
+These choices shape the feature's behavior in ways that benefit from the user's domain knowledge.