feat: browser extension for cookie export (plasmate-extension)

[dbhurley]

Problem

Storing auth cookies via plasmate auth set requires users to manually open dev tools, navigate to Application > Cookies, and copy values by hand. This is error-prone and unfriendly for non-technical users.

Proposed Solution

A lightweight Chrome/Chromium browser extension that exports auth cookies for the current domain in a Plasmate-ready format.

User flow

1. User navigates to a site (e.g., x.com) and logs in normally
2. Clicks the Plasmate extension icon in the toolbar
3. Extension shows relevant cookies for the current domain
4. User clicks "Copy for Plasmate" - copies a CLI command to clipboard:

   plasmate auth set x.com --cookies "ct0=abc123; auth_token=xyz789"
   

5. User pastes into terminal, done

Design principles

• Minimal permissions: only cookies and activeTab (no broad host access)
• No network: extension never phones home, all processing is local
• Tiny: target < 50 lines of core logic, no frameworks
• Smart defaults: for known domains (x.com, github.com), highlight the cookies that matter
• Clipboard only: no direct connection to Plasmate server

Scope

• Chrome Manifest V3 extension
• Popup UI showing domain + cookie list with checkboxes
• "Copy CLI command" button
• "Copy JSON" button (for programmatic use)
• Known-domain presets (x.com: ct0 + auth_token, github.com: user_session + __Host-user_session_same_site)

Out of scope (v1)

• Firefox/Safari ports
• Direct WebSocket connection to Plasmate server
• Cookie monitoring/auto-refresh
• Chrome Web Store publishing (manual install via developer mode initially)

Repository

Code will live in plasmate-labs/plasmate-extension (separate from the engine).

Related: #1 (auth profiles), #2 (auth CLI implementation)