MCP tools fail with 'Browser extension is not connected' despite UI showing connected

Environment

• Claude Code CLI: 2.1.19
• Chrome Extension: 1.0.40
• macOS: 26.3 (Build 25D5087f)
• Chrome: 144.0.7559.97

Issue

The UI reports the Chrome extension as connected, but MCP tool calls fail.

What works (all show success):

• /chrome shows "Status: Enabled", "Extension: Installed"
• /mcp shows "claude-in-chrome · ✔ connected"
• "Reconnect extension" button opens Chrome and shows success
• Native messaging host files exist and are correct

What fails:

• Any MCP tool call (e.g., tabs_context_mcp) returns:

"Browser extension is not connected"

Troubleshooting Attempted

• Reinstalled Chrome extension 5+ times
• Removed and regenerated native messaging host files:
• ~/.claude/chrome/
• ~/Library/Application Support/Google/Chrome/NativeMessagingHosts/com.anthropic.claude_code_browser_extension.json
• Verified all config files are correct
• Restarted Chrome multiple times (Cmd+Q, reopen)
• Started Claude with --chrome flag
• No security software blocking
• No errors in Chrome DevTools console
• Verified user is signed into Claude in extension sidebar

Expected Behavior

When /mcp shows "claude-in-chrome · ✔ connected", MCP tool calls should work.

Actual Behavior

There's a disconnect between what /chrome and /mcp report vs. what the MCP tools actually experience at runtime.