Lazy render collapsed thinking group parts

[roblourens]

Fix #287176

fyi @justschen this is a pretty complicated change to do something seemingly simple, not rendering tool invocations that are collapsed away. Without this, I can scroll through a long chat session and render 100s of tool invocations that aren't displayed, and this is pretty slow.

This is kind of a mess but the thinking part logic is complex. Lmk if there's anything you're concerned about

[Copilot]

Pull request overview

This pull request implements lazy rendering for collapsed thinking group parts to improve performance when scrolling through chat sessions with many tool invocations. By deferring rendering of tool invocations until the thinking section is expanded, the change avoids rendering hundreds of hidden elements.

Changes:

• Introduced factory pattern for creating tool invocation parts, allowing deferred instantiation
• Added lazy item tracking in ChatThinkingContentPart with materialization on first expansion
• Removed unused context parameter from setupThinkingContainer method

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
chatServiceImpl.ts	Commented out isImported check in session storage logic (appears unrelated to lazy rendering)
chatListRenderer.ts	Refactored tool invocation and markdown rendering to use factory pattern for lazy instantiation
chatThinkingContentPart.ts	Added lazy items support with materialization autorun, refactored appendItem to accept factory functions

Comments suppressed due to low confidence (1)

src/vs/workbench/contrib/chat/browser/widget/chatContentParts/chatThinkingContentPart.ts:193

• When lazy items are materialized on expansion, _onDidChangeHeight.fire() is called once after materializing all items. However, individual items may have their own height change listeners (like the autorun at line 1665-1667 in chatListRenderer.ts). This could lead to multiple height updates being triggered. Consider whether firing the height change event once after all items are materialized is sufficient, or if individual item height listeners might cause layout issues.

		// Materialize lazy items when first expanded
		this._register(autorun(r => {
			if (this._isExpanded.read(r) && !this.hasExpandedOnce && this.lazyItems.length > 0) {
				this.hasExpandedOnce = true;
				for (const item of this.lazyItems) {
					this.materializeLazyItem(item);
				}
				this._onDidChangeHeight.fire();

[Copilot]

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resolved