hermes-agent/apps/desktop/scripts/perf

Desktop perf harness

One systematized way to measure desktop rendering/interaction performance, diff it against a committed baseline, and fail on regressions. It replaces the dozen one-off measure-* / profile-* scripts that each reinvented the CDP client, arg parsing, stats, and output (and never had a baseline).

Quick start

# Isolated instance (recommended) — no running app or LLM credits needed.
# Its own --user-data-dir + HERMES_HOME means it never collides with `hgui`.
npm run perf -- --spawn

# Or: launch an isolated instance once, attach repeatedly (faster iteration).
npm run perf:serve            # leaves an instance on :9222
npm run perf                  # attaches, runs the CI suite, gates on baseline

# One scenario, with a CPU profile:
npm run perf -- stream --cpuprofile --tokens 800

# Representative PRODUCTION numbers (minified React, not the ~3x-slower dev build):
npm run perf -- cold-start stream keystroke transcript --spawn --prod

# Re-capture the baseline on your reference device, then commit baseline.json:
npm run perf -- cold-start stream keystroke transcript --spawn --prod --update-baseline

Dev vs prod

By default the harness measures the dev renderer (fast to spin up, good for relative regression checks). Pass --prod (with --spawn) to build a production renderer with the probe included (VITE_PERF_PROBE=1) and measure minified React — the representative shipped numbers. The committed baseline is captured with --prod.

Why isolation matters

The measurement this harness exists to run was historically blocked: a running hgui holds the Electron single-instance lock, so a second instance quit immediately. --spawn / perf:serve launch with their own --user-data-dir (separate lock scope), their own HERMES_HOME (separate backend + sessions), and their own --remote-debugging-port. Synthetic scenarios drive $messages directly via window.__PERF_DRIVE__, so no LLM credits are spent.

Scenarios

scenario	tier	measures	replaces
stream	ci	streaming longtasks, frame p95/p99, mutation cadence	measure-synthetic-stream, profile-synth-stream, profile-long-stream
stream --real	backend	same, from a real LLM stream	measure-real-stream, profile-real-stream
keystroke	ci	composer keystroke → paint latency	measure-latency, profile-typing, leak-typing
transcript	ci	large-transcript mount + paint cost	(new)
cold-start	cold	launch → CDP → driver → first paint (fresh spawn/run)	(new)
first-token	backend	Enter → first assistant token painted (TTFT)	(new)
submit	backend	Enter → cleared → user msg painted, scroll jump	measure-submit, measure-jump
session-switch	backend	route → first-paint → settle	profile-session-switch
profile-switch	backend	rail click → sidebar settled	measure-profile-switch

ci + cold scenarios need no backend/credits and are gated against baseline.json (cold-start requires --spawn since it measures a fresh launch, and must be run in its own invocation). backend scenarios need a live backend (and --spawn or a real session/credits) and are report-only.

CPU profiling is a cross-cutting --cpuprofile flag on any scenario (it wraps the run in Profiler.start/stop and prints a top-self-time table), replacing every standalone profile-* script.

Adding a scenario

Create scenarios/<name>.mjs exporting { name, tier, description, run(cdp, opts) } where run returns { metrics, detail } (metrics = flat numbers, lower is better), then register it in scenarios/index.mjs. If it's ci, add a baseline.json entry (or run --update-baseline).

Layout

• lib/cdp.mjs — the one CDP client + target discovery + typing + CPU-profile wrapper + DOM selectors.
• lib/stats.mjs — percentiles, histograms, CPU-profile self-time ranking.
• lib/baseline.mjs — load/compare/update the baseline + regression gate.
• lib/launch.mjs — attach, or spawn a fully isolated instance.
• scenarios/ — one module per measurement.
• run.mjs — entrypoint. serve.mjs — standalone isolated launcher.

Not migrated (kept as dev utilities)

eval.mjs, reload.mjs, reload-renderer.mjs, probe-renderer.mjs, probe-thread.mjs, click-session.mjs, diag-*.mjs are interactive dev helpers, not benchmarks. They can adopt lib/cdp.mjs in a follow-up.