ui: rendering performance follow-up

[allozaur]

Overview

Follow-up PR with architectural improvements after #26053

Additional information

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: YES, Laguna S2.1 with Zed/llama.cpp

[Copilot]

Pull request overview

Follow-up UI performance work focused on reducing per-render CPU cost during streaming by memoizing expensive parsing/formatting paths and improving tool-result lookup behavior in the chat message renderer.

Changes:

• Add bounded memoization caches for frequently re-run helpers (tool-call JSON parsing, partial JSON scanning, syntax highlighting, LaTeX preprocessing, search-results parsing, tool-result classification/line splitting).
• Replace per-tool-call linear search of tool result messages with an indexed lookup to avoid O(n^2) behavior across many tool calls.
• Add unit tests intended to prevent regressions in tool-call parsing and lookup performance.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tools/ui/tests/unit/parse-toolcalls-memo.test.ts	Adds unit tests for tool-call parsing memoization and tool-message lookup behavior.
tools/ui/src/lib/utils/search-results.ts	Memoizes parsing of tool-result search output and extraction of query from tool args.
tools/ui/src/lib/utils/parse-partial-json-args.ts	Adds a bounded cache around partial JSON arg parsing/scanning.
tools/ui/src/lib/utils/latex-protection.ts	Refactors LaTeX processing to reuse constants and memoizes preprocessing results.
tools/ui/src/lib/utils/code.ts	Adds a bounded cache for highlight.js output keyed by language/autoDetect/code.
tools/ui/src/lib/utils/agentic.ts	Uses Map/Set for faster tool message lookup; memoizes tool result parsing/classification and toolCalls JSON parsing.
tools/ui/src/lib/constants/latex-protection.ts	Introduces reusable LaTeX-related constants/regexes used by the preprocessing pipeline.
tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessage/ChatMessageToolCall/ChatMessageToolCallBlockSearchResults.svelte	Minor cleanup of derived variable typing.
tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessage/ChatMessageToolCall/ChatMessageToolCallBlockEditFile.svelte	Removes an extra blank line.
tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessage/ChatMessageToolCall/ChatMessageToolCallBlockDefault.svelte	Removes unused type import and reorders derived declarations.

Comments suppressed due to low confidence (2)

tools/ui/tests/unit/parse-toolcalls-memo.test.ts:31

• The "returns the same array reference" test doesn't actually assert memoization (or reference identity) and would pass even if JSON.parse runs every time. Consider asserting that JSON.parse is only invoked once for the same toolCalls JSON string across repeated deriveAgenticSections calls.

	it('returns the same array reference for the same JSON string', () => {
		// parseToolCalls is not exported, but deriveAgenticSections uses it
		// internally. We verify memoization through behavior: calling
		// deriveAgenticSections twice with the same toolCalls should not
		// re-parse (which we verify by checking the returned sections

tools/ui/tests/unit/parse-toolcalls-memo.test.ts:124

• This test uses a wall-clock timing assertion (elapsed < 100ms), which is prone to flakes across CI environments and doesn't directly assert the intended regression (avoiding per-tool-call Array#find). A deterministic check is to override toolMessages.find to throw and ensure deriveAgenticSections still succeeds.

		// If the lookup were still O(n^2), this would be noticeably slow
		const start = Date.now();
		const sections = deriveAgenticSections(msg, toolMessages, [], false);
		const elapsed = Date.now() - start;

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[zachwinter]

lovely! probably makes sense to push this through and rebase #26098 onto it once this lands? they're pretty complimentary. either way works for me – just holler.

[allozaur]

lovely! probably makes sense to push this through and rebase #26098 onto it once this lands? they're pretty complimentary. either way works for me – just holler.

yep