Claude in Chrome: Browser extension never connects despite MCP server being registered

Bug Description

The Claude in Chrome browser extension fails to establish a connection between the MCP server and the Chrome browser extension. The MCP server registers successfully (tools are available, /plugin shows it enabled, /chrome command runs), but every call to tabs_context_mcp returns "Browser extension is not connected."

Environment

• OS: macOS (Darwin 25.2.0)
• Claude Code: Latest (native install)
• Chrome: Latest stable
• Model: claude-opus-4-6

Steps to Reproduce

1. Install Claude in Chrome extension from Chrome Web Store
2. Enable the plugin via /plugin in Claude Code terminal
3. Confirm extension shows in Chrome toolbar (visible as "Claude in Chrome" tab with loading spinner)
4. Log into claude.ai in the same Chrome browser with same Anthropic account
5. Run /chrome command in Claude Code
6. Call mcp__claude-in-chrome__tabs_context_mcp with createIfEmpty: true

Expected Behavior

Should return tab context information and establish browser automation session.

Actual Behavior

Every call returns:

Browser extension is not connected. Please ensure the Claude browser extension is installed and running...

Troubleshooting Already Attempted

All of the following were tried with no success:

1. Restart Chrome completely (quit + reopen) — no change
2. Uninstall + reinstall the Chrome extension — no change
3. Remove + re-add plugin via /plugin toggle — no change
4. Remove from settings.json + re-enable — no change
5. switch_browser tool — same "not connected" error
6. /chrome command multiple times — MCP server reconnects but browser bridge never establishes
7. Open claude.ai in Chrome tab — no change
8. Multiple retry attempts (10+) over ~15 minute session — consistently fails

Key Observation

• /plugin output shows: Reconnected to claude-in-chrome — confirming the MCP server side is alive
• The Chrome extension UI shows a loading spinner (see screenshot description: orange "Claude" tab with spinning icon next to "Claude in Ch..." text)
• The MCP tools ARE registered (all mcp__claude-in-chrome__* tools appear in tool list)
• But the WebSocket/bridge between MCP server ↔ Chrome extension never connects

Hypothesis

The MCP server plugin starts and registers tools correctly, but the actual WebSocket connection to the Chrome browser extension fails silently. There may be a handshake or authentication step that doesn't complete, or a port/host mismatch between what the MCP server listens on and what the extension tries to connect to.

Plugin Config Context

{
  "enabledPlugins": {
    "claude-in-chrome@anthropic-agent-skills": true
  }
}

Settings also include other plugins (context7, document-skills, ralph-loop, etc.) — none interfere.