How Flecha is built

Flecha is a Chromium 158 fork. It’s Chromium rather than Electron because Google blocks sign-in in Electron apps; in Chromium, sign-in, extensions and the rest of the web platform work as they do in Chrome.

The fork is kept small on purpose so updating Chromium stays easy. Almost everything you see is a TypeScript extension.

flecha-browser/
├── chromium/
│   ├── patches/      the Chromium patch set, applied in order
│   ├── shell/        the interface, as a built-in MV3 extension
│   ├── native-host/  Node helper: browser import and the MCP server
│   ├── shared/       the Store and code shared by shell and host
│   ├── branding/     names, icons and bundle IDs
│   ├── build/        GN args for dev and release builds
│   └── scripts/      apply, build, run, package, release
└── package.json      npm scripts for the shell and host

The patches

About fifty small patches in chromium/patches/, numbered in the order they apply. They do three kinds of things:

• Make room for the shell. Hide Chromium’s tab strip and toolbar (0002), let the shell’s page draw the window frame (0011–0013, 0017, 0024), and load the shell as a component extension (0021).
• Give the shell what an extension can’t do. A private chrome.flechaPrivate API (0010) for shortcuts that run before the page (0016), the theme (0018), split view with a resizable gap (0019), Flechinha windows (0023, 0025), Peek (0026), DevTools and the default browser (0027), the find bar (0030), and per-Space storage partitions for separate cookies (0034).
• Tidy and package. The “Flecha Browser” profile folder (0001), no Chromium first run (0035), no missing-API-keys bar (0036), Sparkle updates and Check for Updates… (0040, 0053), and the release app’s name, version and bundled shell (0050–0052).

Each patch starts with a one-line description; changed lines in Chromium are marked with // Flecha: comments.

The shell

chromium/shell is a Manifest V3 extension with the ID abdiaepfgbbhdjaecjipmaailijaaide, built with esbuild.

• background.ts, the service worker, holds the Store: Spaces, tabs, folders, favorites, settings. It’s saved in chrome.storage.local.
• ui/ draws the window frame, sidebar, command bar and new tab page. settings.html, boosts.html and flechinha.html are the other pages.
• features/ holds the developer features: Boosts (compiled with sucrase, run through chrome.userScripts), the ad blocker (declarativeNetRequest rulesets built from EasyList and EasyPrivacy at build time), console error counts, responsive view and the local server scanner.

Because the shell is just an extension, UI work needs no Chromium build at all: run.sh loads it from chromium/shell/dist, and npm run shell:watch rebuilds it as you save.

The native helper

A browser can’t read other browsers’ files or listen on a port. chromium/native-host is a Node program that Chromium starts through native messaging (host name dev.oprimo.flecha.host). It only accepts Flecha’s own shell. It:

• reads Arc, Chromium-family, Firefox and Safari data for importing,
• runs the MCP server on 127.0.0.1, forwarding each tool call to the shell, which drives tabs through chrome.debugger.

Release builds carry Node inside the app as Contents/Helpers/flecha-node.

Next: build Flecha from source.