Avoid unnecesary updates to model in new background agent sessions

[DonJayamanne]

No description provided.

[Copilot]

Pull request overview

Adjusts chat input model-selection reinitialization to reduce state churn when a chat session becomes a background session (i.e., the widget’s view model is cleared).

Changes:

• Guarded session-type tracking/model reinitialization so it only runs when currentSessionResource is present.

Comments suppressed due to low confidence (1)

src/vs/workbench/contrib/chat/browser/widget/input/chatInputPart.ts:1944

• With this guard, initSelectedModel() won’t run when the widget transitions to a background session (currentSessionResource becomes undefined), but the handler still calls checkModelInSessionPool() unconditionally. If the currently selected model is session-targeted, checkModelInSessionPool() can call setCurrentLanguageModelToDefault(), which persists the selection and syncs state to _inputModel—and _inputModel is not cleared when ChatWidget#setModel(undefined) is called. Consider also skipping checkModelInSessionPool() (and any other model-syncing work) when e.currentSessionResource is undefined, or explicitly clearing _inputModel when the view model is cleared to avoid mutating the background session’s input state.

			if (e.currentSessionResource && newSessionType !== this._currentSessionType) {
				this._currentSessionType = newSessionType;
				this.initSelectedModel();
			}

			// Validate that the current model belongs to the new session's pool
			this.checkModelInSessionPool();