[BUG] VS Code extension: closing a session tab (×) leaves the claude process and its MCP servers running

Summary

In the VS Code extension, closing a Claude Code tab with the tab's × does not terminate the underlying claude process. The process keeps running (with its stdio MCP servers) until VS Code exits. Blank "new session" views that never received a prompt are affected too, so every opened-then-closed tab leaks a full claude process.

Environment

• Claude Code VS Code extension 2.1.270 (anthropic.claude-code-2.1.270-linux-x64), native binary
• VS Code 1.137.0
• Kubuntu 26.04.1 (Linux 7.0), Node 22.23.1 via nvm
• permissions.defaultMode: bypassPermissions, 4 stdio MCP servers at user scope (gcloud, postgres, chrome-devtools, figma) at the time of the measurement

Steps to reproduce

1. Open the Claude Code panel in VS Code, open a new session tab (no need to type anything).
2. Close that tab with the × on the tab.
3. ls ~/.claude/sessions/ — the <pid>.json for that session is still there; ps -p <pid> shows the native-binary/claude --output-format stream-json process still alive, with its MCP child processes.

Repeat: each open/close cycle adds one process.

What I measured

With 3 tabs actually open, I had 5 claude processes (two with sessionIds that have no transcript in ~/.claude/projects/ at all — blank views closed with ×), later 6 for 3 tabs after a window reload. Each process carried its own 4 stdio MCP servers: 66 MCP processes and ~3.5 GB RSS for Claude Code alone (per-session trees between 260 MB and 1.2 GB).

The extension host log (Claude VSCode.log) for that window shows 6 init and 10 launch_claude webview messages, and no message of any kind when a tab is closed — no dispose/kill/close request reaches the extension side:

$ grep -oE '"request":\{"type":"[a-z_]+"' "Claude VSCode.log" | sort | uniq -c | sort -rn
    155 webview_focused
    117 update_session_state
     77 rename_tab
     ...
      6 init
$ grep -oE 'Received message from webview: \{"type":"[a-z_]+"' … | sort | uniq -c
     10 launch_claude
      2 interrupt_claude

(no close_*, kill_*, dispose_* entries exist)

Expected

Closing a tab disposes the session: the claude process and its MCP children exit, and ~/.claude/sessions/<pid>.json is removed. At minimum, blank views that never received a prompt should be reaped when their tab is closed.

Actual

Process and MCP children keep running until VS Code exits. ~/.claude/sessions/<pid>.json stays. Nothing in the UI shows these sessions, so users cannot see or close them.

Workaround

A cron that kills claude-vscode sessions whose sessionId has no transcript and that are older than 10 minutes (reads ~/.claude/sessions/*.json). Closed tabs that do have a transcript cannot be distinguished from open ones from outside, so those still leak.