Chrome extension connection fails: MCP uses bridge instead of native socket

Bug Description

--chrome mode suddenly stopped working. The MCP tools always return "Browser extension is not connected" even though the native socket connection works perfectly when tested manually.

Environment

• Claude Code version: 2.1.49
• Chrome extension version: 1.0.53
• OS: macOS (Darwin 25.3.0, Apple Silicon)
• Chrome: 145.0.7632.77

Root Cause Analysis

The native messaging socket (/tmp/claude-mcp-browser-bridge-{user}/{pid}.sock) works perfectly - I can connect to it directly and execute tool calls (e.g., tabs_context_mcp) with valid responses including Chrome tab data.

However, Claude Code's MCP layer ignores the local socket and only attempts to connect via the WebSocket bridge (wss://bridge.claudeusercontent.com). Meanwhile, the Chrome extension connects via native messaging (local), not the bridge. The two sides never meet.

Evidence

1. Native socket works - Manual test via Python connecting to the Unix socket with length-prefixed protocol returns valid Chrome tab data
2. Claude Code only uses bridge - lsof shows Claude Code process has TCP connections to bc.googleusercontent.com (bridge) but zero Unix socket connections to the native host
3. No client update occurred - This was working before and broke without any update to Claude Code or the Chrome extension

Likely Cause

The server-side feature flag tengu_copper_bridge appears to have been recently enabled, switching Claude Code from native socket mode to bridge mode. However, the Chrome extension's corresponding flag (chrome_ext_bridge_enabled) may not be enabled, creating a mismatch where:

• Claude Code → connects to cloud bridge (no peer found)
• Chrome extension → connects via native messaging (works locally)
• Result: "Browser extension is not connected"

Steps to Reproduce

1. Start Chrome with the Claude extension installed (v1.0.53)
2. Run claude --chrome
3. Any MCP tool call (e.g., tabs_context_mcp) returns "Browser extension is not connected"
4. Meanwhile, manually connecting to the native socket at /tmp/claude-mcp-browser-bridge-{user}/{pid}.sock works perfectly

Expected Behavior

Claude Code should:

1. Fall back to native socket when bridge has no peer
2. OR ensure feature flags are synchronized between Claude Code and the Chrome extension

Workaround Attempted

• Removed Desktop app native messaging config (com.anthropic.claude_browser_extension.json) so Chrome uses Claude Code's native host → native host runs correctly from Claude Code binary, socket is created and responsive, but MCP still only uses bridge
• Restarted Chrome, reloaded extension, restarted Claude Code, re-logged in → no change

🤖 Generated with Claude Code