chat - slightly improve relayout

[bpasero]

No description provided.

[Copilot]

Pull request overview

This PR refactors the ChatViewPane to improve the relayout logic by extracting the repeated pattern of checking lastDimensions before calling layoutBody into a dedicated relayout() helper method.

Changes:

• Introduced a new relayout() helper method that checks lastDimensions before calling layoutBody
• Replaced all instances of the pattern if (this.lastDimensions) { this.layoutBody(...) } with calls to relayout()
• Removed the fromEvent parameter from updateContextKeys() method and removed the conditional layout call within it
• Added initialization of sessionsViewerVisible field in constructor
• Changed event listener from onDidChangeContentHeight to input.onDidChangeHeight for better specificity

[Copilot]

The condition at line 651 now checks sessionsViewerVisible before sessionsViewerOrientation, but the previous implementation listened to onDidChangeContentHeight which fired when the entire content height changed, not just the input. The new implementation uses input.onDidChangeHeight() which is more specific but may miss other content height changes. Consider whether this narrower event listener could miss legitimate relayout triggers that were previously handled, particularly when chat content (not input) changes height in stacked mode.

See below for a potential fix:

		const maybeRelayoutForStackedSessions = () => {
			if (this.sessionsViewerVisible && this.sessionsViewerOrientation === AgentSessionsViewerOrientation.Stacked) {
				this.relayout();
			}
		};

		// When showing sessions stacked, adjust the height of the sessions list to make room for chat input
		this._register(chatWidget.input.onDidChangeHeight(() => {
			maybeRelayoutForStackedSessions();
		}));

		// Also react to overall chat content height changes, not just input height,
		// to keep stacked sessions layout in sync with expanding/collapsing content.
		this._register(chatWidget.onDidChangeContentHeight(() => {
			maybeRelayoutForStackedSessions();
		}));