The longest-task calculation spread every recorded task into Math.max, which
overflowed the call stack on traces carrying hundreds of thousands of tasks —
the same failure already fixed for collecting trace events.
Adds fixture variants that keep an identical transform animation and vary only
its surroundings — inside a button, under a filtered, clipped, blurred,
transformed or faded ancestor — plus the repository's own spinner overrides
isolated piece by piece. Adds --filler, which pads the page with static
elements, because a variant that costs nothing on a small page is not proven
free in a real document.
All of them measure zero style recalculations per second, including at 15,000
filler elements, which rules out ancestor context, the custom keyframes,
transform-box and document size as explanations for the cost the same spinner
shows inside the application.
Adds `bun run profile:animation`: it serves an isolated fixture and measures
each animation variant directly, so comparing techniques takes seconds instead
of an application rebuild plus a streamed response.
The result is unambiguous and does not vary with element count, measured from 1
to 32: transform, opacity and filter cost zero extra style recalculations, while
the individual rotate property, background-position, border-color and box-shadow
each recalculate style 60 times a second, and geometry properties add layout on
top. Notably `rotate: 360deg` is not a cheap synonym for
`transform: rotate(360deg)`, and will-change, wrapper elements, containment and
stepped timing do not make a non-composited property cheap.
`scripts/perf/DOCUMENTATION.md` documents all four capture commands, how to
stand up a production build to measure against, how to read the artifacts, the
validity guarantees the scripts enforce, and the methodology rules, so this can
be handed to an agent as the entry point for measuring performance. It is linked
from the root guide's documentation anchors.
The theme skill gains an animation contract carrying the measured table, and the
performance skill points at the tooling documentation.
Idle and streaming cost both depend on how much of the sidebar is mounted, so
the scenario setup is now shared. --expand-projects seeds the persisted collapse
state; --expand-sessions clicks every "Show more sessions" control, which
cannot be seeded because pagination is component state. Both run before the
measured window, so it stays input-free. Session expansion must run after the
sidebar has populated, not straight after the load event, or the controls do
not exist yet.
Also replaces a spread push over collected trace events, which overflowed the
call stack once a populated sidebar produced chunks of hundreds of thousands of
events, and the equivalent spread in the heap-maximum calculation.
A CPU sampling profile attributes native work to `(program)`, which during
streaming accounted for three quarters of all busy time and said nothing about
where it went. The timeline trace names that work, so the streaming report now
lists total and maximum time per trace event, skipping container events whose
duration already includes the work below them.
Adds `bun run profile:session`: creates a session, opens it in a real
browser, dispatches a prompt through the supported `openchamber session` CLI,
and records until the session reports itself idle. No input is synthesised, so
everything captured is the app reacting to its own event stream.
Streaming is judged by responsiveness rather than totals, so the report leads
with the long-task distribution, style recalculation and layout rates, frame
production, and the application's own stream counters.
Two failure modes are detected rather than reported as clean results. A session
belonging to a directory the browser is not viewing renders nothing and
produces a perfectly quiet profile, so the run verifies both new message
elements in the DOM and message-list render counters. And `RunTask` is only
emitted under the disabled-by-default timeline category, so a capture without
it reports zero long tasks; the missing-task case is now called out instead of
being shown as zero.
Metric helpers are shared with the idle profiler.
Adds `bun run profile:idle`: a fully unattended capture of what OpenChamber
does while nobody interacts with it. It reports main-thread busy time, style
recalculation and layout rates, DOM node and listener growth, heap trajectory,
a CPU sampling profile, and per-call-site attribution of timer, animation
frame, and observer work.
Chrome throttles timers and stops producing frames for occluded or backgrounded
windows, which silently reports an idle-looking renderer regardless of what the
page schedules. Launch flags now disable that throttling, and every run measures
frame liveness so a throttled capture is reported as a warning rather than as a
clean result.
CDP launch and client code is shared with the existing browser profiler.
Bohdan Triapitsyn