Add unit tests for thinking content part and fix issue with tools/md rendered out of order

[roblourens]

No description provided.

[Copilot]

Pull request overview

This PR adds comprehensive unit tests for ChatThinkingContentPart and fixes an ordering issue where markdown/thinking content was rendered before tool invocations when the content arrived while the thinking section was collapsed.

Changes:

• Added 1043 lines of unit tests covering lazy rendering, display modes (Collapsed, CollapsedPreview, FixedScrolling), state management, content updates, and DOM structure
• Fixed ordering bug by making setupThinkingContainer use lazy rendering when collapsed, ensuring markdown and tool items render in the order they arrive
• Introduced discriminated union type ILazyItem with variants ILazyToolItem and ILazyThinkingItem to handle both tool and thinking items in the lazy rendering queue

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/vs/workbench/contrib/chat/test/browser/widget/chatContentParts/chatThinkingContentPart.test.ts	New test file with comprehensive coverage of ChatThinkingContentPart functionality, including regression tests for the ordering bug
src/vs/workbench/contrib/chat/browser/widget/chatContentParts/chatThinkingContentPart.ts	Refactored lazy rendering system to support both tool and thinking items, ensuring correct DOM ordering when content arrives while collapsed

Comments suppressed due to low confidence (2)

src/vs/workbench/contrib/chat/test/browser/widget/chatContentParts/chatThinkingContentPart.test.ts:951

• The comment on line 951 is confusing. It says "When the id is the same, hasSameContent returns true (other.id !== this.id is false)" but the test name and assertion expect false to be returned. Looking at the implementation (line 946 in the source: return other?.id !== this.id), when the IDs are the same, other.id !== this.id evaluates to false, so the method returns false. The comment should be clarified to: "When the id is the same, other.id !== this.id is false, so hasSameContent returns false"

			// When the id is the same, hasSameContent returns true (other.id !== this.id is false)

src/vs/workbench/contrib/chat/test/browser/widget/chatContentParts/chatThinkingContentPart.test.ts:724

• The test name says "BUG: markdown renders before tools" but this PR fixes that bug, so the test should now be passing and verifying the correct behavior. Consider updating the test name to reflect that this test now validates the fix works correctly, rather than documenting the bug's existence. For example: "markdown via updateThinking should preserve order with lazy tool items (regression test)"

		test('markdown via updateThinking should preserve order with lazy tool items (BUG: markdown renders before tools)', () => {

[Copilot]

The comment on lines 800-804 suggests the bug still exists ("BUG: Currently markdown is always first"), but this PR fixes the bug. Since the assertion expects tool1 to come before markdown (and should now pass with the fix), update this comment to reflect that this is now the correct behavior and the test validates the fix works. For example: "With the fix, tool1 should come before markdown because it was appended first."

This issue also appears in the following locations of the same file:

• line 951
• line 724