# 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`, `parseToolResultWithMedia`, `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
```
