fix: scope editor service in window title to own editor groups container

[yogeshwaran-c]

What kind of change does this PR introduce?

Bug fix

What is the current behavior?

The main window's WindowTitle uses the global IEditorService, which tracks editor groups across all windows including auxiliary windows. When a terminal is moved from the panel to a new auxiliary window via "Move Terminal into New Window", the following sequence occurs:

1. The terminal is removed from the panel group
2. A new auxiliary editor part is created and the terminal opens as an editor there
3. The auxiliary window gains focus
4. The global EditorParts.activePart now returns the auxiliary part (based on getActiveDocument())
5. The global EditorService fires onDidActiveEditorChange
6. The main window's WindowTitle reads editorService.activeEditor, which resolves through activePart to the auxiliary window's terminal editor
7. The main window title incorrectly updates to show the terminal name (e.g. "bash") instead of the open file

This also affects any editor moved to a new auxiliary window, not just terminals.

Closes #267538

What is the new behavior?

Each WindowTitle now receives a scoped IEditorService that only tracks editors within its own window's editor groups container. This is done by creating a child instantiation service with a scoped editor service in the BrowserTitlebarPart constructor:

• For the main window: the editor service is scoped to editorGroupService.mainPart, so it only tracks editors in the main window
• For auxiliary windows: the scoping is consistent with the existing approach used in auxiliaryEditorPart.ts (line 202-203), where a scoped editor service is already created for the auxiliary editor part

After the fix, moving a terminal (or any editor) to a new window no longer affects the original window's title.

Additional context

The auxiliary window's WindowTitle was already getting a correctly scoped editor service via scopedEditorPartInstantiationService (created in auxiliaryEditorPart.ts). The main window's WindowTitle was the only one using the global (unscoped) editor service, which made it susceptible to cross-window active editor changes.

The fix follows the same scoping pattern already established for auxiliary windows but applies it uniformly in BrowserTitlebarPart for all windows.

[vs-code-engineering]

📬 CODENOTIFY

The following users are being notified based on files changed in this PR:

@bpasero

Matched files:

• src/vs/workbench/browser/parts/titlebar/titlebarPart.ts

[bpasero]

This is a really good catch and I wonder if this regressed, I thought I tested this back when aux windows got introduced.

[Copilot]

Pull request overview

Fixes incorrect main window title updates when focus/active editor changes occur in auxiliary windows by ensuring WindowTitle reads a window-scoped IEditorService tied to that window’s editor groups container.

Changes:

• Create a child IInstantiationService in BrowserTitlebarPart that overrides IEditorService with editorService.createScoped(editorGroupsContainer, ...).
• Instantiate WindowTitle via the scoped instantiation service so it only tracks editors within the current window.
• Update editor-action toolbar context gating to use editorGroupsContainer.activeGroup.activeEditor instead of the global editorService.activeEditor.