Bug: MCP calls to Claude in Chrome succeed but return "not connected" error

Observed behavior:

• Claude Code terminal shows "Tabs read" / "Tab created" (success indicators)
• But the actual response received by the model is: Browser extension is not connected. Please ensure the Claude browser extension...
• The request reaches the extension and is processed, but the response data is replaced with an error message

Environment:

• claude mcp list shows: claude-in-chrome · connected
• Extension installed from Chrome Web Store (ID: fcoeoabgfenejglbffodgkkbkcdhcgfn)
• Extension has "On All Sites" permission
• Extension Options page shows approved localhost sites
• macOS Darwin 25.2.0

Troubleshooting attempted:

• Restarted Chrome
• Restarted Claude Code session
• Ran claude extension install-host
• Verified extension permissions
• Extension can read tabs (sidebar shows "Tabs read")

Conclusion:
Request path works (Claude Code → MCP → Extension), but response path fails (Extension → MCP → Claude Code returns error instead of data).

 Here's exactly what I receive back from every call:

  Browser extension is not connected. Please ensure the Claude browser extension is installed and running (https://claude.ai/chrome). If this is your first time connecting to Chrome, you may need to
  restart Chrome for the installation to take effect. If you continue to experience issues, please report a bug: https://github.com/anthropics/claude-code/issues/new?labels=bug,claude-in-chrome

  That's the complete response - no tab IDs, no data, just that error message. Every single time.

  But you're seeing "Tabs read" / "Tab created" on your end, which means the extension IS receiving the request and doing something. The response just isn't making it back to me correctly.

  This looks like a bug in the MCP ↔ extension communication layer.

✻ Cogitated for 31s

❯ try again

⏺ Claude in Chrome[tabs_context]
  ⎿  Tabs read

⏺ Same response:

  Browser extension is not connected. Please ensure the Claude browser extension is installed and running (https://claude.ai/chrome). If this is your first time connecting to Chrome, you may need to
  restart Chrome for the installation to take effect. If you continue to experience issues, please report a bug: https://github.com/anthropics/claude-code/issues/new?labels=bug,claude-in-chrome

  What does your terminal show for this call?

❯ Tabs Read

⏺ That confirms it's a bug. The request succeeds (you see "Tabs Read"), but the response gets replaced with an error message before it reaches me.

  This is worth reporting: https://github.com/anthropics/claude-code/issues

  For now, let's debug the loader issue through code. Can you tell me Shannon Engstrand's userId from the page? I saw 1005517342 as the ID in an earlier screenshot - is that the memberId or userId?

  I'll search the code for what could cause a client-specific loading issue.