longhaul.cpp/tools/ui/tests/client/README-perf.md

Agentic thread perf harness

Two tiers, both reusing the existing vitest projects (see vite.config.ts).

Tier 1 - agentic-stream.perf.svelte.test.ts (project: client, real Chromium)

Mounts ChatMessageAgenticContent and replays a stream, replacing the message object on each chunk exactly as the real pipeline does:

• chat.svelte.ts updateStreamingUI() runs per SSE chunk
• conversations.svelte.ts updateMessageAtIndex does { ...old, ...updates }

That new object identity is the thing under test: it cascades through deriveAgenticSections (which returns fresh AgenticSection objects) into every tool-call block in the message, including completed ones.

npx vitest --project=client --run tests/client/agentic-stream.perf.svelte.test.ts

Reading the output

• mean / p95 / max - the synchronous window per token: prop write, await tick(), then a forced offsetHeight read so style and layout are included rather than deferred.
• sync - sum of those windows. This is the number to optimize.
• wall - the whole run including work MarkdownContent defers into its own requestAnimationFrame. It carries a ~16.7ms/token idle floor because the harness yields a frame each iteration, so compare wall across fixtures, never against sync.

The knobs, and what each one discriminates

The point of the harness is the scaling curve, not any single number.

Knob	Reads on
priorToolCalls (0/1/5/20)	the reactive fan-out. Flat => no fan-out. Linear => confirmed.
toolResultBytes	whole-blob string scans (extractSearchResults, parseToolResultWithImages, classifyToolResult).
editFileEdits	computeLineDiff, the O(m*n) LCS.
openCodeFence	hljs.highlightAuto on partial code.

Deliberately no hard assertions: CI timing is noisy and the value here is the before/after delta, not a gate.

Caveat

This measures one message's subtree. In the real app ChatMessages.svelte rebuilds its whole displayMessages list per token, so multiply by the number of rendered messages to get the conversation-level cost.

Tier 2 - ../unit/agentic-hotpath.bench.ts (project: unit, node)

Per-call costs for the pure functions the curve implicates.

npx vitest bench --project=unit --run tests/unit/agentic-hotpath.bench.ts