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perf(tooling): add an animation cost profiler and document the harness

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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.
This commit is contained in:
Bohdan Triapitsyn
2026-08-03 18:38:58 +03:00
parent 632fc09e18
commit ca31157584
7 changed files with 478 additions and 2 deletions
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.agents/skills/performance-engineering/SKILL.md
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@@ -197,13 +197,19 @@ A cache inside an `O(consumers × entities × candidates)` loop is a mitigation,
## Repository Tooling
Three unattended capture commands exist; prefer them over ad-hoc timing code,
`scripts/perf/DOCUMENTATION.md` is the entry point: it covers every capture
command, how to stand up a production build to measure against, how to read the
artifacts, and the validity guarantees these scripts enforce. Read it before
measuring.
Four unattended capture commands exist; prefer them over ad-hoc timing code,
and extend them when a scenario is missing rather than measuring by hand.
| Command | Answers |
|---|---|
| `bun run profile:idle` | What the app does while nobody interacts with it. Supports `--session`, `--tab`, `--then-tab`, `--panel`, `--expand-projects` to reach a specific mounted state, plus `--baseline` and `--budget-*` for regression gating. |
| `bun run profile:session` | What a streaming assistant response costs. Creates a session, dispatches a prompt through the `openchamber session` CLI, and records until the session reports idle. Reports the long-task distribution, a timeline-trace breakdown, running animations, and output-normalised metrics. |
| `bun run profile:animation` | What a CSS animation costs, isolated from the app. Animate only `transform` and `opacity`; everything else recalculates style every frame. |
| `bun run profile:browser` | A manually driven capture when the interaction cannot be scripted. |
Both automated commands fail loudly rather than reporting a clean result when