Claude in Chrome: extension connected & signed in, but MCP tools report 'not connected' and list_connected_browsers returns [] after mid-session account re-login

Environment

• Claude Code desktop app on macOS (Darwin 25.6.0)
• Claude in Chrome extension: installed, enabled, side panel open and signed in
• Browser tools (mcp__claude-in-chrome__*) worked earlier in the same session

What happened

Mid-session, all mcp__claude-in-chrome__* tools started failing with the standard "Claude in Chrome is not connected" error, and list_connected_browsers returns an empty array [] — even though the extension is installed, enabled, signed in, and its side panel is open (verified via screenshot of chrome-extension://.../options.html).

Timeline:

1. Session started; browser tools worked fine (navigate, javascript_tool, etc. against the user's Chrome).
2. Later in the same session, every browser tool call returns the "not connected" error; list_connected_browsers → [].
3. The user re-logged into the Claude app to make sure both the app and the extension use the same account; extension side panel confirms signed-in state. Still [].
4. Toggling the extension / reopening the side panel did not help. (App restart being tried next.)

Expected

Either the extension reconnects and list_connected_browsers lists it, or the error/tooling gives an actionable reason why the paired extension instance is not visible (account mismatch, stale pairing, transport failure).

Actual

Silent empty list with a generic "not installed or not signed in" hint that doesn't match the observed state — the extension IS installed and signed in. No way to diagnose from either side.

Impact

Browser-dependent workflows (testing staging deployments with the user's authenticated sessions) are blocked mid-task, with no recovery path other than restarting apps blindly.

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