[Windows] Claude in Chrome: "Browser extension is not connected" — native host pipe-name collision (still broken v2.1.212)

[Windows] Claude in Chrome: "Browser extension is not connected" — native host pipe-name collision (still broken v2.1.212)

Summary

On Windows 11, every mcp__claude-in-chrome__* tool call returns "Browser extension is not connected" even though the extension is installed, signed in, the native host manifest is registered, and the named pipe is reachable. The native host exits on startup with a socket-server error caused by a pipe-name collision.

This was previously reported in #58961, which was auto-closed by the inactivity bot without ever being triaged or fixed. It is still fully reproducible on the current release, so I'm re-filing per that bot's instruction.

Environment

| Item | Value |
|------|-------|
| OS | Windows 11 Home 10.0.26200 |
| Shell | Git Bash / PowerShell 7 |
| Claude Code CLI | v2.1.212 (was v2.1.141 in #58961 — regression persists) |
| Chrome | Latest stable |
| Extension | Claude in Chrome (ID fcoeoabgfenejglbffodgkkbkcdhcgfn) |

Reproduction

1. Run claude --chrome
2. Open Chrome with the extension installed and signed in
3. Call any mcp__claude-in-chrome__* tool (e.g. tabs_context_mcp)

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

Root cause (from diagnostics in #58961)

The native host (claude.exe --chrome-native-host) tries to create a listener on
\\.\pipe\claude-mcp-browser-bridge-<user>, but that pipe name is already held by the
running --chrome session. The listener creation fails with Socket server error, and
the extension DevTools shows NATIVE RESULT: Native host has exited. The integration is
left in a half-connected state: the pipe exists and accepts clients, but nothing is serving it.

Confirmed correct (ruled out)

• Native Messaging manifest registered in the Windows registry
• .bat wrapper correctly configured
• Named pipe exists and accepts client connections
• No conflicting CLAUDE_* / ANTHROPIC_* env vars
• Clean state: no Claude Desktop, no stale registry keys, no leftover lock files, competing extensions disabled

Already attempted (no change)

Uninstall/reinstall extension, remove Claude Desktop + its registry keys, disable other
extensions, multiple restarts, clean registry.

Impact

Claude in Chrome appears to be broken for Windows users generally — see the duplicate cluster
#23828, #22890, #23526, and the reports on #58961. Please treat this as a real triage item
rather than letting the inactivity bot close it again.