hermes-agent/apps/desktop/scripts/dev-no-hmr.mjs
Brooklyn Nicholson bff1b3261d perf(desktop): cut per-keystroke layout + listener churn in chat composer
Empirical work via CDP harnesses under apps/desktop/scripts/ (see
profile-typing-lag.md):

  jsListeners growth (per round of 200 chars + GC):
    before: +35  (verified leak — listeners stuck after 1st trigger popover use)
    after:  +0

Four narrow edits in src/app/chat/composer/index.tsx:

1. Drop the per-keystroke `editorRef.current.scrollHeight` read used to
   decide composer expansion. Replace with `draft.length > 60` heuristic;
   the existing ResizeObserver still catches edge cases. `scrollHeight`
   is a forced-layout call and was firing on every char until the first
   wrap.

2. Bucket measured composer height to 8px before writing
   `--composer-measured-height` / `--composer-surface-measured-height`
   on `documentElement`. Without this, the editor grows ~1px per char,
   setProperty fires every keystroke, computed style is invalidated tree-
   wide.

3. Remove the dead `$composerDraft` two-way sync. Nothing outside the
   composer subscribed to that atom (verified via grep). Two useEffects
   on `[draft]` were pushing draft→atom and atom→aui per keystroke for
   no consumer. Also drop the per-keystroke
   `reconcileComposerTerminalSelections` call; it was pruning stale
   labels for `terminalContextBlocksFromDraft`, but that helper already
   ignores labels not in the current submitted text, so pruning per
   keystroke was just bookkeeping.

4. `refreshTrigger` fast-bails when the draft contains neither `@` nor
   `/`. Previously `textBeforeCaret(editor)` ran on every input/keyup
   regardless; `range.toString()` inside is O(n) over draft length.

Synthetic typing latency p50/p90/p99 is similar before vs after on a
freshly-loaded session (Blink can already handle ~30cps typing into a
contentEditable on its own); the real win is the listener leak being
gone and the global computed-style invalidations dropping ~8× when the
composer is sitting at a fixed height row.

The `Enter → stall` follow-up (see profile-typing-lag.md §"Submit /
TTFT stall") is unmeasured here — needs a throwaway session because
the harness fires a real prompt. Not blocking this commit.
2026-05-21 15:45:01 -05:00

22 lines
928 B
JavaScript

#!/usr/bin/env node
// Launch the desktop renderer with HMR disabled so the React Fast Refresh
// preamble path is skipped. This sidesteps a current Vite 8 / plugin-react 6
// bug where the preamble script is not injected into index.html → renderer
// throws "$RefreshReg$ is not defined" on every TSX module → React tree
// never mounts.
//
// We're not trying to use HMR while profiling typing lag anyway. Hermes desktop
// boots, you type, profiler measures. HMR off is fine.
//
// Usage: node apps/desktop/scripts/dev-no-hmr.mjs
// (then in another shell, run electron --remote-debugging-port=9222 .)
import { createServer } from 'vite'
const server = await createServer({
configFile: new URL('../vite.config.ts', import.meta.url).pathname,
root: new URL('../', import.meta.url).pathname,
server: { hmr: false, host: '127.0.0.1', port: 5174, strictPort: true }
})
await server.listen()
server.printUrls()