[BUG] VS Code extension creates empty editor group (blank pane with only X) when opening panel beside Cursor Agents

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Opening the Claude Code panel in a new editor column (e.g. via claude-vscode.editor.open / Claude Code: Open in New Tab) while Cursor's Agents pane is already open creates an extra empty editor group — a blank vertical pane with only a close (X) control and no tabs or content.

This is distinct from editor-group locking (#80148 / #20324 / #7752). Even with the lock call neutralized, the empty column still appears. Closing the empty group (click X) is required after nearly every open; reopening Claude recreates it.

Verified in the shipped extension.js of v2.1.220 (minified; Tt = vscode). createPanel defaults toward ViewColumn.Beside, then overrides that with findUnusedColumn() whenever there is no existing Claude webview group:

createPanel(e, t, r) {
  // ...
  let n = false, i;
  if (r !== undefined) {
    i = r;
  } else {
    i = Tt.ViewColumn.Beside;
    let a = Tt.window.tabGroups.all.find(/* group whose tabs are all claudeVSCodePanel */);
    if (a && a.viewColumn) i = a.viewColumn;
    else i = this.findUnusedColumn(), n = true; // ← bug
  }
  let o = Tt.window.createWebviewPanel("claudeVSCodePanel", "Claude Code", i, /* … */);
  // …
  return { startedInNewColumn: n };
}

findUnusedColumn() {
  let e = new Set;
  Tt.window.tabGroups.all.forEach((t) => {
    if (t.viewColumn !== undefined) e.add(t.viewColumn);
  });
  for (let t = Tt.ViewColumn.One; t <= Tt.ViewColumn.Nine; t++)
    if (!e.has(t)) return t;
  return Tt.ViewColumn.Beside;
}

findUnusedColumn() picks the first absolute ViewColumn number not already claimed by a tab group. Next to Cursor Agents (and other non-standard editor layouts), that absolute column does not match a relative Beside split, so VS Code/Cursor ends up with Claude in one column plus a leftover empty group.

Replacing the call with ViewColumn.Beside (same-length patch: this.findUnusedColumn() → Tt.ViewColumn.Beside||1) stops the empty pane from being created. The lock call on startedInNewColumn is a separate issue (#80148).

What Should Happen?

claude-vscode.editor.open (with no explicit view column) should open Claude in a single new split relative to the active group (ViewColumn.Beside), or reuse an existing Claude column — without leaving behind an empty editor group.

Error Messages/Logs

No error is thrown. Layout after open (Cursor, Agents pane already visible):

1. Claude Code editor tab/group
2. Agents pane ("New Agent")
3. Empty editor group — dark blank area, only an X in the corner

Steps to Reproduce

1. Open a workspace in Cursor with the Agents pane open (right side / Agents UI).
2. Ensure Claude Code is not already open as an editor tab.
3. Run Claude Code: Open in New Tab (claude-vscode.editor.open), or bind that command to a shortcut and invoke it (e.g. ⌘⌥U).
4. Observe a third, empty editor column appear (blank pane with only X), in addition to the Claude panel.

Also reproducible when Agents is open and Claude is summoned from a keybinding that calls claude-vscode.editor.open with no view-column argument.

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Last Working Version

Claude Code Version

anthropic.claude-code 2.1.220 (Cursor extension; also verified call site in 2.1.216)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Cursor

Additional Information

Proposed fix (minimal): in createPanel, when no existing Claude group is found, keep ViewColumn.Beside instead of calling findUnusedColumn():

if (a && a.viewColumn) i = a.viewColumn;
else i = vscode.ViewColumn.Beside, n = true;

Optionally, prefer an already-empty tab group if one exists (tabGroups.all.find(g => g.tabs.length === 0)), then fall back to Beside.

Related:

• #80148 — feature request to opt out of imperative lockEditorGroup (same editor.open / startedInNewColumn path; complementary fix)
• #20324 / #7752 — locked panels left behind
• #79287 — editor focus/group behavior change after 2.1.215
• #79770 — new-tab icon opens session in wrong editor group

Workaround: binary-patch installed extension.js to replace this.findUnusedColumn() with Tt.ViewColumn.Beside||1 (must re-apply after every extension update).

Environment: anthropic.claude-code v2.1.220, Cursor on macOS (Darwin 25.5.0).